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Sol-gel derived bioactive glasses with low tendency to crystallize: Synthesis, post-sintering bioactivity and possible application for the production of porous scaffolds
... The results of the thermal analyses (DSC-TG) regarding both FBG and CBG powders are depicted in Fig. 4. The first peak seen in the DSC curve of FBG at around 150 • C ascribed to the removal of the physically adsorbed water [37]. The weight loss of 10% in the corresponding TG curve also confirms it. ...
... The peak appeared at 233 • C related to the volatilization of chemical water [38]. Three endothermic peaks in the range of 326-550 • C are attributed to the decomposition of the organic precursors and the elimination of nitrate groups [37] exist in the FBG powder. Weight loss for FBG continues up to around 700 • C and can say that all the residuals were removed within this temperature. ...
... FBG curve shows these peaks at around 832 and 928 • C which attributed to the glass transition and crystallization temperatures, respectively. The DSC curve of CBG displays almost similar peaks at 820 and 919 • C. The former temperature is related to the glass transition phenomenon and the later one is ascribable to the glass crystallization [37,39]. ...
Considering the importance of coatings bonding to the substrate, electrophoretic deposition of bioglass coatings reinforced with hydroxyapatite whiskers was performed on anodized titanium substrate. Bioglass powders with both fine particle size (FBG) and coarse particle size (CBG) were used. It was found that Vickers microhardness and bioactivity of the coatings are not affected by titanium anodizing. The enhancement of 58% was obtained for the adhesion strength of FBG based coating due to the interlocking of titania nanotubes with fine bioglass particles entered the voids of nanotubes, which was only 32% for coarse bioglass particles. The microstructure of the coatings demonstrated no changes by anodizing the substrate, while the thickness of the coatings reduced significantly owing to the decreased deposition kinetics. The enhancement of the bactericidal effect and cellular behavior of the coatings indicated the positive impact of the underlaid nanotubes compared with bare titanium. The declined corrosion current density of the coated samples on nanotubes compared to titanium revealed the inhibitory effect of anodizing in terms of corrosion.
... Subsequently, the dried gel was thermally stabilized at 700°C with 1 h dwelling time at 5°C/ min heating rate. 5 ...
... Highly porous micro-pore system will increase scaffold permeability to the external environment, hence, allowing migration of cells through the pores network. 5 The produced scaffolds using sponge sacrificial method exhibited mostly open pores with interconnected pores network, resembling the trabecular bone. 10 Fig . 1 shows the pores microstructure of three different types of scaffolds. ...
... 2,6 Other than that, sample crystallization also results in formation of sodium calcium silicate, Na 2 CaSiO 4 (ICDD 00-001-1067) as previously shown in literature. 5 Nevertheless, all scaffolds did not exhibit any extensive crystallization given that semi-crystallization is the characteristic of bioactive glass materials. In agreement with literatures, sintering temperature at 900°C is thought to be the ideal stabilization temperature as to densify the scaffold and to remove the nitrogen contents. ...
Bioactive glasses (BG) such as 45S5 Bioglass® is one of the most promising scaffold material in bone tissue engineering due to its inherent properties. In this study, 45S5 sol-gel derived bioactive glass scaffolds were fabricated using polymeric sponge replication techniques with the addition of polyvinyl-alcohol (PVA) as binder, and non-ionic block polymer P123 (PEG-PPG-PEG) as co-templates to increase the porosity. The fabricated scaffolds, namely 45S5-PVA (20/80 wt%), 45S5-P123 (20/80 wt%) and 45S5-Mix (20/70/10 wt%) were compared. The scaffolds were characterized using field emission scanning electron microscopy (FESEM), compression test, X-ray diffraction (XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy. The results demonstrated that the fabricated scaffolds exhibited interconnected pore system with dense strut structure. The pores size (in diameter) for all scaffolds were within ideal range and resembling trabecular bone architecture. Interestingly, the addition of polyvinylic binder and pluronic P123 co-template in 45S5-Mix scaffold produced better pore network architecture and increased its compression strength compared to other fabricated scaffolds hence was chosen for further analysis of bioactivity in simulated body fluid (SBF). After immersion in SBF at designated time points: day 3, day 7 and day 14, the formation hydroxyl carbonate apatite (HCA) structure was observed on the scaffold’s surface indicating the bioactivity ability of the sample hence stand as suitable candidate for tissue engineering application.
... However, the high tendency of bioactive glasses to crystallize during thermal treatments, which are required for several manufacturing processes, such as the production of scaffolds (but also coatings and composites), has been the main obstacle to the broader diffusion of these materials in medical applications. In the last few years, some researchers have focused on the development of novel bioactive glasses with higher thermal stability (which means low tendency to devitrification) with respect to 45S5 [35][36][37][38][39]. ...
... Aspects of biocompatibility (cytotoxicity and genotoxicity), osteogenesis, and angiogenesis of different glasses have been investigated in order to identify the most promising bioactive glasses to be employed as possible substitutes in bone tissue regeneration and, more recently, in the treatment of infections. In particular, the literature suggests that the behavior of the main proteins (such as collagen, alkaline phosphatase, bone morphogenetic proteins (BMP2), transforming growth factor beta (TGF-β), fibroblast growth factors (FGFs)) involved in the process of the formation of new bone is determined by the ions present in the glass compositions [2,15,19,35]. The general mechanism of a bioglass used in medicine for bone regeneration or dental trauma can be explained as follows: after the implantation of a bioactive glass exposed to (body) fluid, some surface reactions occur that ensure the formation of a deposit of a calcium phosphate layer [20]. ...
The use of bioactive glasses in dentistry, reconstructive surgery, and in the treatment of infections can be considered broadly beneficial based on the emerging literature about the potential bioactivity and biocompatibility of these materials, particularly with reference to Bioglass® 45S5, BonAlive® and 19-93B3 bioactive glasses. Several investigations have been performed (i) to obtain bioactive glasses in different forms, such as bulk materials, powders, composites, and porous scaffolds and (ii) to investigate their possible applications in the biomedical field. Although in vivo studies in animals provide us with an initial insight into the biological performance of these systems and represent an unavoidable phase to be performed before clinical trials, only clinical studies can demonstrate the behavior of these materials in the complex physiological human environment. This paper aims to carefully review the main published investigations dealing with clinical trials in order to better understand the performance of bioactive glasses, evaluate challenges, and provide an essential source of information for the tailoring of their design in future applications. Finally, the paper highlights the need for further research and for specific studies intended to assess the effect of some specific dissolution products from bioactive glasses, focusing on their osteogenic and angiogenic potential.
... A weak endothermic peak around 150 • C can be observed in the DTA curve, which indicates the desorption of physically adsorbed water and dehydration of hydroxide. A weight loss of about 10% up to 200 • C is attributed to these reactions [51,[56][57][58]. The second sharp endothermic peak around 300 • C corresponds to the decomposition of organic precursors and the condensation of the silanol groups [57,58]. ...
... A weight loss of about 10% up to 200 • C is attributed to these reactions [51,[56][57][58]. The second sharp endothermic peak around 300 • C corresponds to the decomposition of organic precursors and the condensation of the silanol groups [57,58]. The exothermic peak at around 400 • C corresponds to the removal of incompletely reacted precursors and mainly to the elimination of residual carbon by the oxidation process. ...
A low-temperature method was developed to produce bioactive glass microspheres (BGMs). The microspheres were fabricated by dispersing the prepared sol in silicon oil, a process called the sol-microemulsion-gel method. The resulting microspheres were characterized by X-ray diffractometry (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Brunauer-Emmett-Teller (BET) techniques. Furthermore, the effect of various processing parameters such as reaction chamber size and the stirring rate on microspheres diameter was investigated. The results indicated that under optimized conditions, one could obtain BGMs with acceptable sphericity having a narrow size distribution. The obtained microspheres had diameters in the range of 19.3±9.3 μm. The BET specific surface area was 240.33 m²/g. The results also showed that the increase in the reaction chamber size had interesting contradictory effects on BGMs diameter. The increase in the stirring rate intensified the shear forces exerted on the water phase and caused the generation of smaller droplets and microspheres.
... The commercial raw powders reagents (SiO 2 , Na 2 CO 3 , CaCO 3 , K 2 CO 3 , Ca 3 (PO 4 ) 2 by Carlo Erba Reagenti, Rodano-Milano, Italy) were melted at 1450°C in a platinum crucible for 1 h to produce the bioactive glass BG_Ca/Mix [24][25][26]. Such bioactive glass has the following composition: 47.2 mol% SiO 2 , 45.6 mol% CaO, 2.3 mol% K 2 O, 2.3 mol % Na 2 O, and 2.6 mol% P 2 O 5 [26]. ...
... The commercial raw powders reagents (SiO 2 , Na 2 CO 3 , CaCO 3 , K 2 CO 3 , Ca 3 (PO 4 ) 2 by Carlo Erba Reagenti, Rodano-Milano, Italy) were melted at 1450°C in a platinum crucible for 1 h to produce the bioactive glass BG_Ca/Mix [24][25][26]. Such bioactive glass has the following composition: 47.2 mol% SiO 2 , 45.6 mol% CaO, 2.3 mol% K 2 O, 2.3 mol % Na 2 O, and 2.6 mol% P 2 O 5 [26]. Subsequently, the melt was rapidly quenched in water (at room temperature) to obtain a frit, which was dried at 110°C for 12 h and then milled into powder form, with grain size below 45 μm. ...
In this work, HA/bioactive glass Functionally Graded Materials (FGMs) are obtained for the first time by means of Spark Plasma Sintering (SPS). Two series of highly dense 5 layered products, namely FGMS1 and FGMS2, are prepared under optimized SPS conditions, i.e. 1000 °C/2 min/16 MPa and 800 °C/2 min/50 MPa, respectively, using a die with varying cross section.
Results arising from XRD, SEM, mechanical and biological characterization in SBF, evidence that lower temperature and higher-pressure levels used for FGMS2 samples provide better materials in terms of microstructure, compactness, hardness, elastic modulus and in vitro bioactivity. Indeed, a fully sintered and crack-free microstructure with no crystallisation at the top layer (100% bioactive glass) is correspondingly produced.
The obtainment of such FGMs is quite promising, since it permits to vary the relative volume fractions of the two constituents and, consequently, tailor the biological response for specific clinical applications.
... Its first clinical use in an implant was aimed to replace small bones in the middle ear to treat conductive hearing loss [27]. Since then, the possible applications in the biomedical field have been widely studied [28][29][30][31][32][33][34][35][36][37]. ...
... MTT is a fast colorimetric assay founded on the cleavage of a yellow tetrazolium salt to purple formazan crystals, through mitochondrial enzymes in metabolic-active cells. It is applied to appraise indirect toxicity and cell viability by spectrophotometry [34]. 96 well-cultured plates were utilized to culture cells in contact with samples extract and incubated for 24 and 72 h. ...
(1) Background: a cell evaluation focused to verify the self-regenerative antioxidant activity is performed on cerium doped bioactive glasses. (2) Methods: the glasses based on 45S5 Bioglass®, are doped with 1.2 mol%, 3.6 mol% and 5.3 mol% of CeO2 and possess a polyhedral shape (~500 µm2). Glasses with this composition inhibit oxidative stress by mimicking catalase enzyme (CAT) and superoxide dismutase (SOD) activities; moreover, our previous cytocompatibility tests (neutral red (NR), 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Bromo-2-deoxyUridine (BrdU)) reveal that the presence of cerium promotes the absorption and vitality of the cells. The same cytocompatibility tests were performed and repeated, in two different periods (named first and second use), separated from each other by four months. (3) Results: in the first and second use, NR tests indicate that the presence of cerium promotes once again cell uptake and viability, especially after 72 h. A decrease in cell proliferation it is observed after MTT and BrdU tests only in the second use. These findings are supported by statistically significant results (4) Conclusions: these glasses show enhanced proliferation, both in the short and in the long term, and for the first time such large dimensions are studied for this kind of study. A future prospective is the implantation of these bioactive glasses as bone substitute in animal models.
... 3. The samples' bioactivity in SBF increased when the amount of BGCaMIX in the sample is augmented. 4. Finally, the biocompatibility of BGCaMIX and of HA/BGCaMIX composites with different HA to glass ratio, produced by conventional sintering, has been successfully tested with respect to murine osteocytes and/or fibroblasts [24,37]. ...
... Here, for the first time, the biocompatibility of a set of pure HA, pure BGCaMIX and HA/BGCaMIX composites produced by SPS was evaluated with respect to murine long bone osteocytes by means of both direct (NR uptake) and indirect test (XTT and BrdU). It should be noted that, although previous works [24,37] confirmed the biocompatibility of both BG-CaMIX and HA/BGCaMIX composites produced by conventional sintering, analogous investigations regarding bioglasses and bioglass-based composites sintered by SPS are lacking in the literature. ...
The biocompatibility of hydroxyapatite (HA), a lab-made bioglass (BGCaMIX) with high crystallization temperature and different HA/BGCaMIX composites, produced by Spark Plasma Sintering (SPS), was tested with respect to murine osteocytes both by direct and indirect tests, in order to also investigate possible cytotoxic effects of the samples’ extracts. Previous investigations demonstrated that the samples’ bioactivity, evaluated in a simulated body fluid solution (SBF), increased with the increasing amount of BGCaMIX in the sample itself. Although none of the samples were cytotoxic, the findings of the biological evaluation did not confirm those arising from the SBF assay. In particular, the results of direct tests did not show an enhanced “biological performance” of materials with higher glass content. This finding may be due to the high release of ions and particulate from the glass phase. On the contrary, the performance of the BGCaMIX alone is better for the indirect tests, based on filtered samples’ extracts. This work further demonstrates that, when considering bioglasses and HA/bioglass composites, the results of the SBF assays should be interpreted with great care, making sure that the results arising from direct contact tests are integrated with those arising fromthe indirect ones.
... 3. The samples' bioactivity in SBF increased when the amount of BGCaMIX in the sample is augmented. 4. Finally, the biocompatibility of BGCaMIX and of HA/BGCaMIX composites with different HA to glass ratio, produced by conventional sintering, has been successfully tested with respect to murine osteocytes and/or fibroblasts [24,37]. ...
... Here, for the first time, the biocompatibility of a set of pure HA, pure BGCaMIX and HA/BGCaMIX composites produced by SPS was evaluated with respect to murine long bone osteocytes by means of both direct (NR uptake) and indirect test (XTT and BrdU). It should be noted that, although previous works [24,37] confirmed the biocompatibility of both BG-CaMIX and HA/BGCaMIX composites produced by conventional sintering, analogous investigations regarding bioglasses and bioglass-based composites sintered by SPS are lacking in the literature. ...
The biocompatibility of hydroxyapatite (HA), a lab-made bioglass (BGCaMIX) with high crystallization temperature and different HA/BGCaMIX composites, produced by Spark Plasma Sintering (SPS), was tested with respect to murine osteocytes both by direct and indirect tests, in order to also investigate possible cytotoxic effects of the samples’ extracts. Previous investigations demonstrated that the samples’ bioactivity, evaluated in a simulated body fluid solution (SBF), increased with the increasing amount of BGCaMIX in the sample itself. Although none of the samples were cytotoxic, the findings of the biological evaluation did not confirm those arising from the SBF assay. In particular, the results of direct tests did not show an enhanced “biological performance” of materials with higher glass content. This finding may be due to the high release of ions and particulate from the glass phase. On the contrary, the performance of the BGCaMIX alone is better for the indirect tests, based on filtered samples’ extracts. This work further demonstrates that, when considering bioglasses and HA/bioglass composites, the results of the SBF assays should be interpreted with great care, making sure that the results arising from direct contact tests are integrated with those arising fromthe indirect ones.
... Thanks to the peculiarities of BG_Ca/Mix, it was possible to sinter the HA-based composites at lower temperatures with respect to samples with the same HA/Bioglass ® ratio, thus reducing the crystallization of the glassy phase and avoiding the decomposition of HA and/or reactions between HA and glass. The in vitro biocompatibility of both BG_Ca-Mix and of HA/BG_Ca-Mix composites has been successfully proved in recent investigations [28,32]. ...
... The same temperatures would be inadequate to sinter 45S5, which has been reported to reach a full densification only after thermal treatments between 1050°C and 1100°C [45,46] which cause a wide crystallization of the final system with the formation of Na 2 Ca 2 Si 3 O 9 and Na 2 CaSi 2 O 6 phases [34,45,46]. Recent biocompatibility tests performed with murine osteocites and fibroblasts demonstrated the high osteoconductive potential of both BG_Ca/Mix sintered powders and of HA/BG_Ca-Mix composites [28,32]. Based on these encouraging results, it was conceivable that the produced materials could induce bone growth in vivo in an animal model. ...
In this work a set of novel materials for bone tissue regeneration have been tested in vivo in an animal model. In fact, despite many studies have been devoted to amorphous 45S5 Bioglass®, there is lack in the literature of works aimed to study the in vivo performance of heat-treated – and thus partially crystallized – 45S5. As widely reported, crystallization limits the bioactivity of 45S5 and is the main reason that prevents a broader use of this material. Thus, in the present work, a recently developed bioactive glass (BG_Ca/Mix) is tested, since previous investigations demonstrated that BG_Ca/Mix is particularly promising by virtue of both its high bioactivity and lower tendency to crystallize with respect to 45S5. BG_Ca/Mix sintered powders and two composites, which contain BG_Ca/Mix and an increasing percentage (20 wt% or 70 wt%) of hydroxyapatite (HA), were considered. As a term of comparison, 45S5 sintered powders were also studied. The samples were implanted in rabbits' femurs and harvested after 8 weeks. The histological analysis demonstrated that BG_Ca/Mix has an osteoconductive ability slightly higher than that of 45S5 glass-ceramics, followed by that of the composites, which may represent the starting point for obtaining systems with degradation rate tailored for a given clinical application. Moreover, the 45S5 samples were locally cracked, probably because of a non-uniform dissolution in the physiological environment. On the contrary such cracks, which could lead to implant instability and unsuitable mechanical performance, were not observed in BG_Ca/Mix.
... At 600-800 • C, the remaining components and byproducts (such as nitrate) that were produced during the hydrolysis and condensation processes are removed from the gel (Mukundan et al., 2013;El-Rashidy et al., 2017). The pore diameter, pore volume, and surface area of the bioactive glass improved significantly after these six processes were implemented (Bellucci et al., 2014;Durgalakshmi et al., 2014). The bioactive glass created has been reported as having a better and faster response with bodily tissue (Owens et al., 2016), has higher purity and is more homogeneous in structure (Jones, 2015). ...
This study introduces a templating approach using a cellulosic suspension to create a porous SiO2–CaO–P2O5–Na2O bioactive glass material. Sol-gel approach was used as the synthesis method. Carbon nanofibers in suspension form was used as the templating material. The amount of CNF used in the experiment ranged from 5% to 25% by volume. The morphology, porosity, crystallinity of the combeite phase, mechanical and chemical properties of the BG samples were examined. The findings show that the templating method had no effect on the formation of the required functional elements, such as Si, Ca, Na and P. The porosity of the BG materials improves by 15% after templating compared to the neat sample. The formed pores were assumed to be homogenous based on the uniform adsorption and desorption BET profiles. The crystallization mechanisms during the sintering process were affected by the templating approach, indicating the need for a specific amount of template to be used in the preparation step. Both the sintering temperatures and the CNF content affected the formation of the combeite phase. The BG samples had excellent mechanical properties and are suitable for use in cancellous bone applications. As a result, this study shows a novel method for synthesizing porous bioactive glass materials via the sol-gel method and a CNF suspension as a template.
... Brittle Slow degradation except TCP-excessive dissolution,fast degradation, post-implantation reactions, imbalanced osteogenicity (Bellucci et al., 2014;Bian et al., 2014;Goel et al., 2012;Gu et al., 2013;Hoppe et al., 2011;Sarker et al., 2015;Sriranganathan et al., 2016;Dorozhkin, 2010;Lei et al., 2017;Mondal et al., 2018;Yang et al., 2018;Ke et al., 2017;Lee et al., 2017;Taktak et al., 2018;Yang et al., 2015a;Liu et al., 2016;Shokrollahi et al., 2017;Shuai et al., 2015) Natural polymer (Mimics to ECM, biocompatibility, Enzymatic biodegradability, Structural Complexity, Poor mechanical strength) Collagen/Gelatin (Denaturalized collagen) ...
Bone is dynamic tissues have structural and functional complexity with varying mechanical strength as of skeletal, craniofacial maxillary position. Despite surgery, allograft, advanced therapy, treatment of critical defects, deformities and functional restoration of bone are still challenging. BTE provides the hope, which could resolve the surgical challenges by developing the artificial functionalized bone. Use of biodegradable polymers in BTE provides variable required mechanical properties, porosity, and surface microenvironment for cellular adhesion, osteoblast proliferation and differentiation. Non-antigenic, immunomodulatory, vascularization, cytocompatibility, adjustable degradation kinetics, hydrolytic/enzymatic degradation and release of biocompatible metabolites are the main characteristics that enable biodegradable polymers for making 3D-scaffold for BTE. In the above line, this article illustrates the different biodegradable polymers that useful for the bone microenvironment and for the repair bone tissues.
... However, this technique incurs higher energy costs, and often results in partial devitrification with the formation of crystalline phases, which have reduced biological properties and are unsuitable for producing porous scaffolds [11]. Due to this, the sol-gel method has been regarded as a favourable alternative, as it yields glasses with higher purity, requiring low densification temperatures and allowing the production of a varied amount of compositions [31,32]. This technique does, however, exhibit some drawbacks-namely, the high cost of the precursors, and the difficulty in producing dense, monolithic pieces [33]. ...
Sol–gel synthesis using inorganic and/or organic precursors that undergo hydrolysis and condensation at room temperature is a very attractive and less energetic method for preparing bioactive glass (BG) compositions, as an alternative to the melt-quenching process. When properly conducted, sol–gel synthesis might result in amorphous structures, with all of the components intimately mixed at the atomic scale. Moreover, developing new and better performing materials for bone tissue engineering is a growing concern, as the aging of the world’s population leads to lower bone density and osteoporosis. This work describes the sol–gel synthesis of a novel quaternary silicate-based BG with the composition 60 SiO2–34 CaO–4 MgO–2 P2O5 (mol%), which was prepared using acidified distilled water as a single solvent. By controlling the kinetics of the hydrolysis and condensation steps, an amorphous glass structure could be obtained. The XRD results of samples calcined within the temperature range of 600–900 °C demonstrated that the amorphous nature was maintained until 800 °C, followed by partial crystallization at 900 °C. The specific surface area—an important factor in osteoconduction—was also evaluated over different temperatures, ranging from 160.6 ± 0.8 m2/g at 600 °C to 2.2 ± 0.1 m2/g at 900 °C, accompanied by consistent changes in average pore size and pore size distribution. The immersion of the BG particles in simulated body fluid (SBF) led to the formation of an extensive apatite layer on its surface. These overall results indicate that the proposed material is very promising for biomedical applications in bone regeneration and tissue engineering.
... On the other hand, the P O P band ascribed to the HCA phase starts to appear after day 7. In fact, the obtained spectra are in accordance with the synthetic HCA ones, with changes related to the intensity of the typical HCA bands, located near 1255, 1130, 1055, 605, and 560 cm −1 [31][32][33][34]. Also, the C O band of HCA starts to be detected after 21 days [35]. ...
In the bone tissue engineering field (BTE), it is of significant importance to develop bioactive multifunctional scaffolds with enhanced osteoconductivity, osteoinductivity, and antibacterial properties required for lost bone tissue regeneration. In this work, a bioactive glass-ceramic scaffold was manufactured via a novel polymer-derived ceramics (PDC) manufacturing method. To gain antibacterial properties, the silver ions were incorporated in controlled amount along with other precursors in the PDC processing stage. Microstructural and structural properties of the fabricated silicate-phosphate glass-ceramic scaffold were evaluated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis, respectively. Furthermore, bioactivity, antibacterial, and cytotoxicity evaluation of PDC scaffolds were conducted. The microstructural analysis determined that scaffolds have interconnected porous network with two different pore range size favorable for osteointegration and bone formation. The structural analysis confirmed that fabricated glass-ceramic scaffolds contain bioactive octacalcium phosphate (OCP) phase responsible for enhanced bioactivity and HCA formation during the immersing of scaffolds in simulated body fluid (SBF) for several days. Moreover, PDC scaffolds with Ag nanoparticles showed considerable antibacterial properties against Gram-negative Klebsiella pneumoniae and Gram-positive Staphylococcus aureus bacteria cells. This study has demonstrated that it is possible to develop a novel group of antibacterial and bioactive Ag incorporated silicate-phosphate glass-ceramic scaffolds for BTE applications, such that, it was verified in vivo.
... The sol-gel approach provides various benefits over traditional melting techniques. It allows extremely fine powders to be produced, using a highly regulated composition that necessitates only moderate processing temperatures in order to produce bioactive glass with higher purity and homogeneity than that produced using the traditional melting technique; the sol-gel method also assists with the regulation rates of ion dissolution in physiological solutions [6]. ...
A modified sol-gel method was used in the current work to prepare a 13-93 bioactive glass powder, which was selected for the therapeutic actions of its constituent parts. In particular bioactive glass 13-93 can chemically bond with host tissue and induce osteogenesis. The produced gel was calcined at a temperature of 600 °C, while particle size analysis and x-ray diffraction were performed after the preparation of the glass powder. Porous bioactive glass 13-93 scaffolds were synthesised using the polymer foam replication technique that uses polyurethane sponges as a template. Sintering at 700 °C was then performed for one hour to the produce the required structures. After sintering, the microstructure was examined by scanning electron microscope (SEM) and Fourier transform infrared analysis (FTIR). The x-ray diffraction (XRD) results were also examined. The average particle size of bioactive glass 13-93 thus produced was about 2.978 μm, and XRD pattern analysis showed that the porous scaffolds were amorphous. The microstructure of the 13 – 93 glass scaffolds contained interconnected cellular pores and a dense network of bioactive glass, allowing scaffolds with porosity between 80 and 83% to be obtained. An in vitro bioactivity test was performed on the scaffolds by soaking them in a solution of simulated body fluid (SBF). The subsequent SEM images confirmed the bioactivity of the prepared scaffolds based on the formation of obvious and dense hydroxyapatite particles on the surface after 7 days of immersion in SBF. It was thus concluded that bioactive glass scaffold prepared in this work via the polymer foam replication technique has the potential to be used in several future applications.
... Aside from requiring lower processing temperature compare to melt derive route, sol-gel method also has multiple advantages. There has been scholar literature reporting that sol-gel method can produce bioactive glass with better homogeneity and purity [7]. Gel-derived bioactive glass can be bioactive in broader range of composition as compare to melt-derived bioactive glass and it has enhance dissolution rate due to its high surface area [8]. ...
Sol gel derived bioglass was well known for its better bioactivity due to its higher surface area in comparison to the melt derived bioglass. In this studies, a new bioglass 54S4P (54 wt% SiO2, 22 wt. % CaCO3, 20 wt. % Na2O, 4 wt. % P2O5) was successfully fabricated through sol-gel route. 54S4P bioglass were aged at three different aging temperatures (25°C, 40°C and 60°C). This synthesized glass was analyzed using X-ray Powder Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Whereas the bioactivity of the optimized samples were observed through in-vitro test using Hank's Balanced Salt Solution (HBSS) at different soaking time (1, 3, 7 and 14 days). XRD confirmed the primary crystalline phase was Na4Ca4Si6O18. The result indicate that the crystalline patterns in gel-derived glass aged for 60°C days exhibit stronger peaks compare to samples aged at 25°C and 40°C. This could be attributed to the difference of water content inside the gels. Apatite formation on the BG surface with characteristic of carbonate group (C-O) and P-O band noticed from FTIR and morphology of apatite formation on BG surface was observe using SEM.
... Certain glass compositions, such as 45S5, suffer from crystallization phenomena at relatively low temperatures, limiting their use in enamelling processes. The addition of alkaline oxides into a bioactive glass [108][109][110] allows one to increase the crystallization temperature, and this helps to limit the devitrification during the enamelling process. Coatings with interesting local mechanical properties and crack-free interface with the titanium substrate were developed, starting from bioactive glasses with low tendency to devitrification [111,112]. ...
Bioactive glasses are promising biomaterials for bone and tissue repair and reconstruction, as they were shown to bond to both hard and soft tissues stimulating cells towards a path of regeneration and self-repair. Unfortunately, due to their relatively poor mechanical properties, such as brittleness, low bending strength and fracture toughness, their applications are limited to non-load-bearing implants. However, bioactive glasses can be successfully applied as coatings on the surface of metallic implants to combine the appropriate mechanical properties of metal alloys to bioactivity and biocompatibility of bioactive glasses. In this review, several available coating techniques to coat metal alloys using bioactive glasses are described, with a special focus on thermal spraying, which nowadays is the most used to deposit coatings on metallic implants.
... The discovery of sol-gel chemistry in 1991has been given rise to a new generation of bioactive glasses [19]. One of the most attractive characteristics of the sol-gel method is allowing researchers to obtain nano-systems based on sol-gel bioactive glass as nanoparticles and nanofibers, which are promising candidates in biomedical applications [20]. However, the biodegradation rates of BGs are usually slow compared to some kinds of bioresorbable ceramics (such as, tricalcium phosphate and brushite). ...
This work was mainly aimed to synthesize new ceramic composites based on nano-bioactive glass (nBG) and magnesium phosphate ceramic (MgP) with different ratios using the sol-gel approach in order to overcome the limitations of both materials. The glass was based on 85SiO2-10CaO-5P2O5 (mole %), and MgP was based on the formula; Mg3(PO4)2. The obtained composites were characterized by DTA, XRD, FTIR, SEM/EDX and Zeta potential techniques. The in vitro bioactivity test was carried out in SBF, and the cell viability test was conducted by culturing the composites with human normal fibroblast cell line (BJ1). The results of XRD analyses showed that there were often no strong diffraction peaks detected which indicated the amorphous nature of the ceramic composites. Moreover, soaking of the ceramic composites in SBF exhibited that addition of MgP to nBG was increased the degradation of the latter one, and nBG was improved the formation of apatite crystals on MgP ceramic. Moreover, the cell viability results showed that MgP was showed significant higher viability than nBG at high concentrations, and it improved the viability of nBG in the ceramic composites.
... The sol-gel 45S5 BG precursors composing of tetraethylorthosilicate (TEOS), triethyl phosphate (TEP), calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) and sodium nitrate (NaNO3) were synthesized following a slight modification from previously reported method [8]. 33.5 mL TEOS were added into 50 mL of 1M nitric acid and allow to react for 1 hour for acid hydrolysis. ...
Bioactivity is an important aspect in biomaterial science ensuring materials used are safe for clinical application. The study describes fabrication of composites containing polylactic acid (PLA) – polyethylene glycol (PEG) with incorporation of sol-gel derived 45S5 bioactive glass (BG). Thermal analysis via Differential Thermal Analysis shows a favorable point over degree of crystallization that influence cells attachment, although non-significant difference in values indicates BG has homogenously dispersed. This correlates to X-ray diffraction analysis where non-significant difference is seen in intensities of the diffraction peaks, which confirms low impact of BG brittleness properties over the fabricated composite. Composites’ pH and degradation study in Simulated Body Fluid shows a steady increment profile over time and lower degradation rate for the composite after incorporation of BG. In vitro cell proliferation study also showed that HDF cells seeded on composite film of P/BG2.5 exhibit highest cell viability with steady increment of proliferation throughout the observation period.
... The sol-gel route is frequently used to produce silicate particles [21][22][23][24] with high homogeneity and controllable composition [21,25]. The formation of a silicate matrix under room temperature leads to an easy and low-cost [26] method. ...
Objective:
The aim of this study is to produce sol-gel derived calcium silicate particles (CS) and evaluate the influence of different concentration of calcium tungstate in the physical, chemical, mechanical and biological properties of developed cements.
Methods:
Sol-gel route were used to synthesize calcium silicate particles that were characterized with x-ray difraction, Fourier transformed infrared spectroscopy, scanning electron microscopy, laser diffraction and nitrogen absorption. Cements were formulated with the addition of different concentrations of calcium tungstate (CaWO4), resulting in four experimental groups according to the CS:CaWO4 ratio: CS100 (100:0), CS90 (90:10), CS80 (80:20), CS70 (70:30). The setting time, radiopacity, compressive strength, pH, calcium release, cell proliferation and cell differentiation were used to characterize the cements.
Results:
CS particles were succesfully sinthesized. The addition of CaWO4 increased the radiopacity and did not influenced the setting time and the mechanical properties of cements. The pH of distilled water was increased for all groups and the CS100 and CS90 groups presented incresed calcium release. Reduced cell viability was found for CS70 while CS100 and CS90 presented higher ALP activity and % of mineralized nodules after 21 days.
Significance:
Sol-gel derived CS particles were sucssfully developed with potential to applied for the production of bioactive ceramic cements. The addition of 10% of CaWO4 resulted in cements with adequate properties and bioactivity being an alternative for regenerative endodontic treatments.
... The lesion was well demarcated within the lacrimal gland and enucleoresection was performed. The periorbital fascia was relocated and the lateral orbital rim was reinserted in its correct anatomic position and fixated with previous pre-platted two microplates and screws (Fig. 2b) [13], without the need for a bone substitute [14][15][16][17][18][19][20][21]. A drain tube was placed; the muscular fascia, subcutaneous tissue and skin suturing is performed without any local flaps [22]; a firm compressive dressing is applied for 48 hours and then removed. ...
To report a case of acinic cell carcinoma occurred in the lacrimal gland. A 59-year-old man was admitted because of sudden blurring of vision, progressive proptosis of the left eye, and mild double vision in left and down directions of the gaze (Hess-Lancaster test). His medical history detailed controlled bilateral keratoconus and open angle glaucoma. On examination, the best corrected visual acuity decreased from 8/20 till 1/50 in one week. There was a swelling of the left upper eyelid. A hard and tender mass was palpated in the superior temporal left orbit. Ultrasound scan showed an extraconal solid mass, situated in the superior lateral corner of the orbit. Computed tomography and magnetic resonance imaging (MRI) revealed a mass of two centimeters in diameter, with round well-defined outline, within the lacrimal gland. We performed an enucleoresection of the mass, via a coronal approach and a lateral orbitotomy by a piezosurgical device. The lesion appeared nodular, brownish, measuring about 2 × 1.5 cm. Histopathological findings were consistent with acinic cell carcinoma with a microcystic, focally papillary-cystic growth of pattern. Follow-up MRI outcomes led to removal of the residual lacrimal gland for suspicion of recurrence. No tumor recurrences where detected at 7-year follow-up.
... Our research focuses on the addition of therapeutic ions, such as zinc, fluoride, gold, copper, gallium, and cerium to these bioglasses [8][9][10][11][12][13][14][15][16]. The resulting glasses are bioactive and their behavior is comparable to Hench and Kokubo bioglasses. ...
(1) Background: valuation of the bioactivity and cytocompatibility of P2O5-free and CeO2 doped glasses. (2) Methods: all glasses are based on the Kokubo (K) composition and prepared by a melting method. Doped glassed, K1.2, K3.6 and K5.3 contain 1.2, 3.6, and 5.3 mol% of CeO2. Bioactivity and cytotoxicity tests were carried out in simulated body fluid (SBF) solution and murine osteocyte (MLO-Y4) cell lines, respectively. Leaching of ions concentration in SBF was determined by inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (ICP-OES). The surface of the glasses were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. (3) Results: P2O5-free cerium doped glasses are proactive according to European directives. Cerium increases durability and retards, but does not inhibit, (Ca10(PO4)6(OH)2, HA) formation at higher cerium amounts (K3.6 and K5.3); however, cell proliferation increases with the amount of cerium especially evident for K5.3. (4) Conclusions: These results enforce the use of P2O5-free cerium doped bioactive glasses as a new class of biomaterials.
... All the compositions, i.e., BG_Ca-Mix, modified BG_Ca-Mix compositions with MgO and/or SrO and HA/BG_Ca-Mix composites have been successfully tested in vitro in terms of biocompatibility [9,15]. In another very recent paper [16], sintered samples of the BG_Ca-Mix family and specific HA/BG_Ca-Mix composites have been tested in vivo in an animal model, showing promising results. ...
In this work, a set of novel bioactive glasses have been tested in vivo in an animal model. The new compositions, characterized by an exceptional thermal stability and high in vitro bioactivity, contain strontium and/or magnesium, whose biological benefits are well documented in the literature. To simulate a long-term implant and to study the effect of the complete dissolution of glasses, samples were implanted in the mid-shaft of rabbits’ femur and analyzed 60 days after the surgery; such samples were in undersized powder form. The statistical significance with respect to the type of bioactive glass was analyzed by Kruskal–Wallis test. The results show high levels of bone remodeling, several new bone formations containing granules of calcium phosphate (sometimes with amounts of strontium and/or magnesium), and the absence of adverse effects on bone processes due to the almost complete glass dissolution. In vivo results confirming the cell culture outcomes of a previous study highlighted that these novel bioglasses had osteostimulative effect without adverse skeletal reaction, thus indicating possible beneficial effects on bone formation processes. The presence of strontium in the glasses seems to be particularly interesting.
... For glass powders, high specific surface area (Table 1) and high superficial porosity (Fig. 3E and F) were obtained and this is found for other glass compositions produced through sol-gel route [28]. Sol-gel derived glasses usually present greater specific surface area when compared No. of to melt derived ones due to solvent evaporation upon heating treatments in glass synthesis [2,29]. This porosity is not only responsible for increased surface area but also for irregular nanoarchitecture in particle surface which has been shown to increase cell migration, adhesion and extracellular matrix production [25,33]. ...
... Another study prepared Sr-MBG scaffolds by the typical polymer sponge method and showed similar porous structure with pore size ranging roughly from 300 to 500 µm compared to the present study (150 -400 µm). This isprobably due to different criteria of PU foam having 20 ppi (32) . ...
... Several types of materials known from the literature are used for hard tissue engineering [7][8][9][10]. The most widely used ones are bioactive glasses [11][12][13][14][15], calcium phosphate-based cement and ceramics, biodegradable polymer-based composites, and special alloys (Ti, Zr) etc. [16][17][18][19][20][21]. All the materials have numerous advantages but none of them fulfil the requirements completely. ...
Replacement of damaged or missing bone tissue is a serious problem in orthopedic surgery. Although various artificial materials are available, none of them fulfil the requirements completely. In this study, new bone substitute materials, silica aerogel-based β-tricalcium phosphate, and hydroxyapatite composite ceramics, along with a control sample were synthesized and tested. Porosities and pore size distribution curves were determined by nitrogen gas adsorption/desorption porosimetry, and surface morphology changes were studied by scanning electron microscopy. Bioactivities were tested in vitro by soaking the samples in simulated body fluids (SBF). Three new advanced SBFs containing eight essential amino acids and bovine serum albumin were developed, extending the complexity of the original simulated body fluid in order to approximate the human blood plasma’s composition more accurately. Each sample was treated with SBF1–SBF4 for two weeks. According to our results, it seems to be necessary to re-evaluate hydroxyapatite deposition as proof of bioactivity of artificial bone substitutes when synthetic body fluids analogous in their composition to human blood plasma are used in studies.
... Sol-gel glasses can be produced at low temperature conditions with good homogeneity. The sol-gel method offers potential benefits for obtaining the powdered materials with good control of composition, microstructure, and wider range of bioactivity (Ahmed et al. 2012;Bellucci et al. 2012;Goller et al. 2004;Arcos and Vallet-Regíl 2010). Sol-gel process is a more convenient technique than melt quenching technique to improve HCA layer growth rate in simulated body fluid (SBF) solution based on dissolution property of synthesised glass-ceramics in SBF solution. ...
Barium soda lime phosphosilicate [(58SiO2–(32 − x)BaO–xCao–6Na2O–4P2O5 (where x = 15, 20, 25 and 30 mol%)] samples were synthesised using conventional sol–gel method at 700 °C sintering temperature. Thermal, structural properties were studied using thermo gravimetric analysis and differential thermal analysis, X-ray diffraction, scanning electron microscopy, fourier transform infrared and Raman spectroscopy. Using Raman spectra non-bridging oxygen concentrations were estimated. The hydroxy-carbonated apatite (HCA) layer formation on samples was analysed for 7 days using simulated body fluid (SBF) soaked samples. The growth of HCA layers self-assembled on the sample surface was discussed as a function of NBO/BO ratio. Results indicated that the number of Ca²⁺ ions released into SBF solution in dissolution process and weight loss of SB-treated samples vary with NBO/BO ratio. The changes in NBO/BO ratios were observed to be proportional to HCA forming ability of barium soda lime phosphosilicate glasses.
... Remarkably, PED allows to conserve the target stoichiometery into the growing film: indeed, at the ablation event, all target material components are ejected simultaneously regardless the evaporation enthalpy and transferred to the film maintainig the compositional relations of the target. This fact enables the manufacturing of thin films composed of complex materials in a single process step [20,21] The biocompatibility of CaK has been also previously demonstrated in vitro [25]. ...
Due to poor mechanical properties and brittleness of bioactive glasses, the deposition of bioactive glass coatings on bioinert metallic implants for bone regeneration is a promising route to combine the high bioactivity of the glassy phase with the mechanical strength of metallic substrate. The Pulsed Electron Deposition (PED) technique has been recently demonstrated to be an effective method to fabricate highly-adherent and nanostructured bioactive thin films and coatings, with fine control over film composition. In this paper, we investigated the deposition by PED of 45S5 Bioglass® and of a novel CaO-rich bioactive glass, also containing potassium oxide. Composition, microstructure, surface morphology, wettability and adhesion to the titanium substrate were assessed for both as-deposited and annealed coatings. All samples exhibited a nanostructured surface morphology and high hydrophilicity, both positive features for biological applications. In particular, annealed samples exhibited increased roughness and adhesion degree to the titanium substrate compared to the as-deposited ones. The results showed in this paper suggest that bioactive glass coatings deposited by PED are promising for being further investigated as bioactive coatings for bone implants.
... The composite structure of bone matrix strongly influences the natural bone mechanical properties. Bioactive glass and glass ceramics are fillers for bioactive composites, since they can integrate into the body and can form biologically active apatite (Hydroxy apatite) layer at the bone/implant interface [1][2]. It is important to note that, bond between the bone and a glass material is the precipitation of an apatite layer on the surface of the glass material which is responsible for bioactivity. ...
In the present work, we report on the effect of the CaO/Na2O ratio on Non-Bridging Oxygen/Bridging Oxygen (NBO/BO) ratio for sol-gel synthesized 58SiO2-(38-x)CaO-xNa2O-4P2O5 glasses and establish the correlation between Hydroxy Carbonated Apatite layer (HCA) forming ability and the dissolution behaviour in simulated body fluid (SBF) solution. Thermal stabilities were calculated as 221, 135, 153 and 77 °C respectively. It is inferred that thermal stabilities varied nonlinearly with CaO/Na2O ratio. Similarly NBO/BO ratios were obtained using Raman spectroscopic analysis as 0.6293, 0.7917, 0.2264 and 0.3513, respectively. All samples were soaked in the SBF solution for 7 days. The calculated weight losses of these samples were 55.32, 69.13, 18.09 and 20.08 for the corresponding NBO/BO ratios. The decrease in CaO/ Na2O ratio led to nonlinear variation of the NBO/BO ratios. Consequently the non linear variation in NBO/BO ratio led to the nonlinear variation of HCA forming ability of SBF treated samples.
Alkali and alkaline earth elements play a crucial role in the structure, processing, and properties of bioactive glasses, widely used in medical applications since their inception in 1969.
A native glass nanoparticle composition based on a binary system, “BGNPs,” was synthesized by a modified Stöber process under surfactant. Afterward, the glass was doped with silver (Ag), and their acellular bioactivity was studied. The synthesized bioactive glasses were characterized by thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BJH), X-Ray diffraction (XRD), nuclear magnetic resonance (NMR) and Scanning Electron Microscope attached with Energy-dispersive X-ray spectroscopy (SEM-EDS). Further, biological properties were analyzed before and after in-vitro tests by soaking the as-prepared bioglass nanoparticles in simulated body fluid (SBF) for different periods. Apatite layers covered the surface of the prepared nanoparticles, indicating their bioactivity from SEM images. Also, the pore size distribution of nano-spheroids particle sizes was within the range of 2–5 nm, and quantitative results from the EDS confirmed the Ag-doped in BGNPs, and both SEM and XRD spectra validated the above results. Using silver-doped prepared glasses, promising results were obtained regarding apatite formation.
Bone involvement promoted by aging and accidents has raised interest in biomaterials and biofabrication technologies for bone regeneration purposes. Thus, 3D printing technology has gained prominence in the production of scaffolds due to its versatility in producing complex geometries with interconnected pores. In this work, composite scaffolds of poly (lactic acid) (PLA), bioglass (BG) and carbon nanotubes (CNT) were produced by 3D printing, using hexagonal, honeycomb-like geometry interspersed. The samples were analyzed in terms of chemical structure, crystallinity and morphology using Fourier transform infrared spectroscopy and Raman spectroscopy, X-ray diffraction and scanning electron microscopy, respectively. The thermal stability of the composite was evaluated by thermogravimetry and the mechanical properties by compression tests. The cell viability was determined by Alamar Blue. The results that raman spectroscopy confirmed the interaction of BG in the polymer matrix by new peaks in the spectrum between 1400 and 2600 cm−1 and the presence of the D, G and 2D bands of the CNTs. In terms of compressive strength, PLA scaffolds with 2 mm inner spacing demonstrated higher compressive strength of 14.88 ± 2.35 MPa, while PLA/CNT higher apparent compressive modulus of 0.58 ± 0.36 GPa. In cell viability, statistical tests showed that there was no significant difference between scaffolds with 2 and 4 mm inner spacing.
Bioglass is extensively used in clinical and bone tissue engineering, more specifically in orthopaedic as bone substitute in the form of granules or powders because of their excellent bioactivity, biodegradability and biocompatibility. They have the capability to form an integrated bond with bone through degradation and biomineralization at the surface of the living tissues. These activities are mainly driven by the composition, synthesis method and crystallinity of the bioglass. Therefore, in this paper we aimed at reviewing the basics and methods used in assessing the crystallization process of bioglasses and a few insights into crystallization revealed in the recent years. This critical review helps in tailoring and controlling crystallinity for their better applicability.
This work deals with the preparation of freeze-cast scaffolds using a bioactive glass from the SiO2–CaO–Na2O–P2O5–K2O–MgO system. This material could be sintered at lower temperatures (650 °C) than other variations of bioactive glasses, which is an important advantage in terms of energy and cost savings. This behavior represents a great advantage in terms of energy and cost savings. The freeze-casting step was conducted using water as a solvent and liquid nitrogen as a coolant. The prepared samples were examined according to their pore structure, thermal behavior, mechanical stability, and bioactivity. The glass transition temperature (Tg), crystallization onset temperature (Tx), and maximum crystallization temperature (Tc) evaluated for this bioactive glass were about 660 °C, 690 °C, and 705 °C. Consequently, the freeze-cast scaffolds could be sintered at 650 °C for 2–8 h, which favored viscous flow sintering without crystallization. Bioactivity assays were conducted by soaking the scaffolds in simulated body fluid for up to 21 days, showing that these materials present a bioactive behavior, inducing hydroxyapatite formation. These materials' mechanical properties and biocompatibility make them promising candidates for use in trabecular bone repair.
Smart biomaterials have been rapidly advancing ever since the concept of tissue engineering was proposed. Interacting with human cells, smart biomaterials can play a key role in novel tissue morphogenesis. Various aspects of biomaterials utilized in or being sought for the goal of encouraging bone regeneration, skin graft engineering, and nerve conduits are discussed in this review. Beginning with bone, this study summarizes all the available bioceramics and materials along with their properties used singly or in conjunction with each other to create scaffolds for bone tissue engineering. A quick overview of the skin-based nanocomposite biomaterials possessing antibacterial properties for wound healing is outlined along with skin regeneration therapies using infrared radiation, electrospinning, and piezoelectricity, which aid in wound healing. Furthermore, a brief overview of bioengineered artificial skin grafts made of various natural and synthetic polymers has been presented. Finally, by examining the interactions between natural and synthetic-based biomaterials and the biological environment, their strengths and drawbacks for constructing peripheral nerve conduits are highlighted. The description of the preclinical outcome of nerve regeneration in injury healed with various natural-based conduits receives special attention. The organic and synthetic worlds collide at the interface of nanomaterials and biological systems, producing a new scientific field including nanomaterial design for tissue engineering.
The “shuttle effect” in lithium-sulfur cell causes the terrible cycles stability, that hinders the Li-S batteries served as the next generation high energy density batteries. To address the issue, we investigated that anatase/bate crystal phase titanium dioxide nanotubes (TiO2 NTs) combined with reduced graphene oxide (RGO) to modify the initial polypropylene separator. The TiO2 NTs/RGO film not only localizes the migrating polysulfides by the common effects of chemical binding and physical adsorption but also enhances the lithium-ion migration by reducing the electrochemical resistance. The excellent chemical and physical adsorption ability were proved by the measurement of the X-ray photoelectron spectroscopy and adsorption experiments. The fast lithium-ion migration was analyzed by the diffusion experiment and electrochemical impedance systems. The outstanding initial discharge capacity of 1303.3 mAhg⁻¹ at 0.2 C, which was 78% of the theoretical capacity. Over 100 cycles, the cell with TiO2 NTs/RGO coating separator still retained 620.6 mAhg⁻¹ discharge capacity. The TiO2 NTs/RGO modifying separator exhibits great promise to develop the high energy Li-S batteries.
In this study, borate-based 13–93B3 bioactive glass powders were synthesised through a sol-gel method using tributyl borate as the boron precursor. Any gel formation was not observed in the glass sol during processing and upon the solvent evaporation, a gel-like layer was obtained. Calcinations were performed between 450 °C and 625 °C in air atmosphere to decompose the nitrates leading to the formation of metal oxides in the glass network. Results showed that use of high calcination temperatures to remove the nitrates from precursor materials caused the formation of partially crystalline structures. In vitro mineralisation experiments revealed that synthesised powders calcined at 550 °C converted to hydroxyapatite phase after immersion in simulated body fluid for 1 day. It was concluded that sol-gel- derived 13–93B3 glass powders have enhanced bioactivity and can be an alternative to conventional melt-derived borate-based bioactive glasses synthesised at much higher temperatures.
The bioactive glass powders have been synthesis by sol-gel method at low temperature. The silica used as the starting material in this study is silica purified from natural sand with mass variations for amorphous silica and phase variations (Quartz, amorphous). Analysis of the FTIR curves in samples BA1, BA2, BA3 and BQ showed that a lot of group bonds on Bioactive Glass had been formed for all samples. There are Si-O symmetric stretching functional groups (823-825 cm ⁻¹ ), Si-O-Si symmetric stretching functional groups (1047-1050 cm ⁻¹ ), PO4 functional groups (579-606 cm ⁻¹ ), as well as OH symmetry and asymmetry functional groups (3414-3435 cm ⁻¹ ). Meanwhile, the UV-Vis curve reveals the absorption of ultraviolet wavelengths in the range of 230-300 nm for all samples. Although the trend of sample density (BA1, BA2 and BA3) with the SiO 2 -amorphous starting material was indicated to decrease with the increase in mass, respectively 0.555 gram/cm ³ , 0.553 gram/cm ³ and 0.543 gram/cm ³ , the highest density was achieved by the BQ sample of 0.563 gram/cm ³ . This density value is still higher than the density of bone tissue so that further synthesis is needed by adding an amorphous SiO 2 starting material.
Sol-gel prepared nanostructured bioactive glass has superior osteoconductivity compared to micron-sized bioactive glass materials. Herein, we reported on the choice of acid catalysts in bioactive glass synthesised by sol-gel method and its effect on altering the nano-structure, crystallization and in vitro apatite. Bioactive glass-HNO3 has sodium calcium silicate (Na2Ca2Si3O9) compounds after sintering. Whereas in the case of bioactive glass -HCl, wollastonite (CaSiO3) based crystallization is formed in the silica network. The apatite formation on the surface of bioactive glass synthesized using HCl as a catalyst is 75% higher compared to bioactive glass synthesized using HNO3, even at very low immersion time of 8 h. The intermediated washing and drying of sintered bioactive glass samples show enhanced apatite formation and negligible NaCl crystallization on the reactive surface. The results of the present work elaborate the importance on the role of an acid catalyst in the sol-gel synthesis of nanostructured bioactive glass, which will be helpful for its large scale production with enhanced bioactivity.
Objective:
The aim of this study was to incorporate sol-gel-derived bioactive glass as filler into experimental adhesive resins and evaluate the influence of glass composition on the physicochemical and biological properties of the developed adhesives.
Materials and methods:
Sol-gel particles were produced with or without the addition of niobium (BAGNb or BAG, respectively). The produced particles were incorporated (2wt%) into experimental adhesive resins formulated with 66wt% bisphenol A-glycidyl methacrylate and 33wt% hydroxyethyl methacrylate. Ethyl dimethyl-4-aminobenzoate and camphorquinone were used as photoinitiator system. Two experimental groups were produced: ABAGNb and ABAG. The adhesive without particles was used as control (ACG). The materials were tested for their degree of conversion, softening in solvent, and cytotoxicity. The mineral deposition was analyzed by Raman spectroscopy. Flexural strength and immediate and 1-year microtensile bond strength were evaluated.
Results:
No statistical difference was found in degree of conversion. ABAGNb showed reduced softening and higher mineral deposition than ACG and ABAG after 28 days. ABAG and ABAGNb resulted in higher cell viability and lower flexural strength when compared to ACG. After 1-year, ABAGNb and ABAG presented statistically significant lower μTBS values.
Significance:
Sol-gel-derived bioactive glasses promoted increased mineral deposition and cell viability for experimental adhesives with increased phosphate content and longitudinal μTBS values for the ABAGNb group. These results suggest the potential of the studied particles to be applied as bioactive fillers for dental adhesives. Reductions in longitudinal μTBS and flexural strength, however, were observed for both glasses compositions and must be considered.
In the present work, we have synthesized the 58SiO2-(38-x) CaO-xAg2O-4P2O5 glasses using sol-gel method and these glasses were treated for 7 days in simulated body fluid (SBF) solution. The structural properties of SBF treated samples were studied using characterization techniques such as X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Dissolution studies also have been studied for SBF treated samples. The XRD pattern indicates that crystalline nature increases with increase in Ag2O for synthesizing samples. The formed Hydroxy Carbonated Apatite (HCA) particles were identified by XRD and EDX analysis. Dissolution studies confirmed that HCA formation decreased with Ag2O content. Finally, it was confirmed that Ag2O content resists the HCA formation.
Electrophoretic deposition of bioactive glass (BG) coatings reinforced by whisker hydroxyapatite (WHA) particles was investigated in this work. Different BG powders as freeze dried (FBG) with fine particle size and calcined (CBG) with coarse particle size were used. Hydroxyapatite with whisker morphology reinforced microstructure of BG composite coatings and improved their mechanical properties. CBG and FBG coatings with 50 and 75 wt% WHA respectively, showed the highest bonding strength and bioactivity response as optimum coatings. Combination of WHA and BG particles had synergistic effect on the generation of apatite layer on the coatings during bioactivity test. Cellular behavior was influenced by surface roughness and environment alkalinization generated by BG dissolution. Finer particle size of FBG compared to CBG had positive effect on bioactivity and antibacterial characteristics of the coatings due to its rapid dissolution. FBG powder calcination conducted simultaneously with sintering of corresponding coated samples without negative effect on BG characteristics.
Bone tissue engineering has been continuously developing since the concept of "tissue engineering" has been proposed. Biomaterials that are used as the basic material for the fabrication of scaffolds play a vital role in bone tissue engineering. This paper first introduces a strategy for literature search. Then, it describes the structure, mechanical properties and materials of natural bone and the strategies of bone tissue engineering. Particularly, it focuses on the current knowledge about biomaterials used in the fabrication of bone tissue engineering scaffolds, which includes the history, types, properties and applications of biomaterials. The effects of additives such as signaling molecules, stem cells, and functional materials on the performance of the scaffolds are also discussed.
Bioactive ceramics, glasses and glass ceramics have the ability to enhance the bone formation and bond to surrounding tissue. In this study, we report on the synthesis of mesoporous nanobioactive glass ceramic with the modified composition of quaternary system 50% SiO2 - 26% Na2O - 20% CaO- 4% P2O5 (Ca/P: 5) [i.e.50S20C] by sol-gel method and succeeded by heat treatment. The as-dried sample was calcined at various temperatures such as 100 °C, 300 °C, 500 °C, 700 °C and 900 °C for 24 h.The weight loss measurement was carried out using Thermogravimetric (TG) analysis. The structural features were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM) & Energy Dispersive Spectroscopy (EDS) analysis. The results revealed that the synthesized glass ceramic stabilized at higher temperature (700 °C and 900 °C)making more formation of the crystalline phase of sodium calcium silicate. The density and porosity measurements were carried out by using the Archimedes immersion method. The mechanical properties of the glass ceramic exhibit the compressive strength as69 MPa and 72 MPa for 700 °C and 900 °C, respectively. From the obtained results, we confirmed the calcined bioactive glass ceramic nanoparticles at 700 °C and 900 °C having a better crystallization, crystallite size with high surface area, high density, suitable porosity of mesoporous with dense microstructure and adequate mechanical properties. Furthermore, in vitro bioactivity character of calcined nanobioactive glass ceramics were studied by using an immersion of nanopowders into Stimulated Body Fluid (SBF) solution for two different time periods such as 7 and 14 days. After soaking the glass ceramic nanopowders in SBF, the structural and morphological changes were determined by using XRD, FTIR and FESEM & EDS analysis, respectively. The in vitro results exhibited that crystallization did not retard the samples bioactivity which indicates the increase of material bioactivity while calcining temperature was increased and it is used to fabricate tissue engineering scaffolds with sustained mechanical properties. Moreover, the enhanced bactericidal behavior of glass ceramic has also been studied. An antibacterial study revealed that the prepared bioactive glass ceramic show a significant effect on two bacteria E. coli and S. aureus.
Nanosized bioactive glass (NBG) particles are attractive materials for bone repair because of their ability to enhance bone formation and to chemically bond to the surrounding bone tissue. In recent years, composites of biopolymers and NBG particles have been developed for bone tissue engineering due to their increased bioactivity, biocompatibility, and biodegradability. In this paper, the authors review current knowledge regarding polymer/NBG composites, including nanoscale‐related features and ion‐release effects of bioactive glass (BG) with respect to osteogenic and angiogenic responses in vivo and in vitro; the authors also focus on the techniques used to fabricate these nanocomposites. Additionally, this review discusses recent developments in the use of nanocomposites for tissue engineering and represents a literature update, as well an expansion, of previously published articles on this topic.
The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.
Biomaterials play a crucial role to improve the quality of life of patients who need a medical implant. The present chapter is focused on those biomaterials which can be made by sol-gel processing and particularly on the developments achieved in the last decade. The chemistry involved in sol-gels permits to drastically improve the properties of biomaterials which are addressed here by order of increased sophistication. In a first section, traditional biomaterials and their synthesis by sol-gel are described. After a brief summary of the properties required for a biomaterial and of sol-gel processing, the materials addressed comprise the calcium phosphates, the so-called bioglasses based on sol-gel silica and their shaping as porous scaffolds, and the organic hydrogels. In a second section, the bioactivity tests applied to biomaterials, as well as the bioactivity mechanisms considered to operate in bioglasses, are summarized. A third section is focused on sol-gel TiO2 based biomaterials, while the next section is dedicated to sol-gel composites and hybrid organic-inorganic gels. The latter group includes a summary of the challenge to introduce calcium in hybrids. A last section concerns the highest present degree of sophistication aimed in biomaterials, which is the entrapment of bioactive molecules in the gels, such as growth factors. The aim is that such additives must be progressively delivered to the surrounding tissues during the lifetime of an implant, so as to improve its biocompatibility for a longer time span. © Springer International Publishing AG, part of Springer Nature 2018.
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It is extremely difficult to produce pure amorphous bioglasses from a quaternary system containing sodium, as they are readily prone to crystallisation, leading to inhomogeneity in the final glass matrix. Moreover, the aging time required in sol-gel synthesis is the main barrier to using the sol-gel method widely, compared with other preparation methods such as the melt quenching method. Typically, ageing times of one week or more are required to achieve an amorphous glass. Similar problems exist in the synthesis of bioceramics with sol-gel, in which unwanted phases may form irreversibly, or the desired phases may form with large crystallite size, as a result of slow ageing.
To overcome this problem, we have developed an innovative, rapid sol-gel method for producing bioglass and bioceramic nanopowder, which avoids the conventional lengthy ageing and drying processes. This is 200 times quicker in comparison to conventional aqueous sol-gel bioglass preparation, and 50 times quicker than standard sol-gel bioceramic methods.
In this chapter we summarise the existing work on conventional sol-gel synthesis of such bioglasses and bioceramics, as well as some other, more rapid methods. We then give details of the novel sol-gel protocol developed by us to synthesise a quaternary glass (with incorporation of Na2O) in only 1 h. A comparative study of sol-gel derived glasses made by this novel rapid route using rotary evaporator drying, and a lengthy conventional route using oven drying and aging, revealed that the two methods produce stabilised bio-glasses with virtually identical behaviour and properties.
We also expand on using this rapid method to produce pure hydroxyapatite (Ca10(PO4)6(OH)2, HAp) bioceramics, obtained after only 1 h with no prior ageing step. The rapid developed process favoured the formation of smaller/finer nanopowders, while producing pure HAp virtually identical to that obtained from the slow conventional drying method.
Indeed, both rapidly dried powders for HAp and bioglass possessed enhanced properties such as smaller crystallite sizes, larger surface areas, and the silica network in the glass matrix exhibits a lower degree of polymerisation. All these enhanced properties should in turn result in increased bioactivity.
Changes in the surface structure of K-208 glass after single-time irradiation of its samples with 20-keV electrons and protons are studied using atomic-force microscopy. Irradiation is performed in a vacuum chamber under a pressure of 10–4 Pa; the densities of the electron (ϕe) and proton (ϕр) fluxes are varied in the range of 10¹⁰–2.5 × 10¹¹ cm⁻² s⁻¹. Analysis of the samples irradiated in the case where the parameters ϕe and ϕр increased in a stepwise manner makes it possible to study the appearance, growth, and evolution of microscopic structures on their surfaces. The radiation-stimulated processes of defect annealing and the release and field diffusion of alkali metal ions are accompanied by crystallization of the irradiated glass layer, which gives grounds for the use of dislocation mechanisms for mass transfer in explaining the formation of microprotrusions on its surface. It is shown that the character of changes in the structure is determined by the values of the parameters ϕe and ϕр and the ratio between them. In particular, it is established that, in the case of electron— proton irradiation of the glass, electrostatic discharges begin to noticeably affect the formation of microprotrusions for ϕе > 3ϕр.
In the last years, bioactive glasses and glass-ceramics drew the attention for their application in the production of implants. Among them, Bioglass® 45S5 is the most commonly used in terms of bioactivity, but its sintering behavior and the related glass-ceramics strongly depend on the followed synthesis process. For these reasons, this paper reports a comparison of the properties and the thermal behavior of bioactive 45S5 glasses produced by a conventional melting process starting from suitable solid precursors or an innovative sol-gel procedure.
The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological (i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.
Bioactive glasses react chemically with the body fluids. The reaction product is an apatite, which, with the intervention of biological drivers, assists the generation of bone matrix and bone growth. The main application of these bioactive glasses in the clinical field is the filling of osseous cavities, manufacture of small parts for middle ear bone replacement and maxilofacial reconstruction and dental applications. Thanks to advances in related medical technologies, bioactive glasses are now undergoing a new stage of development, resulting in different mechanical properties, drug delivery capabilities, bioactive coating of metallic implants, protein and/or cell activation for tissue regeneration and tissue engineering, and are also finding use in biomimetics, nanotechnology, production of hybrid organic-inorganic materials and as bioactivity accelerators of mineral apatites or as bioactivity inductors of magnetic materials for hyperthermia treatment of osseous tumours. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Bioceramic "shell" scaffolds, with a morphology resembling the cancellous bone microstructure, have been recently obtained by means of a new protocol, developed with the aim to overcome the limits of the conventional foam replication technique. Because of their original microstructure, the new samples combine high porosity, permeability, and manageability. In this study, for the first time, the novel bioactive glass shell scaffolds are provided with a gelatin-based biomimetic coating to realize hybrid implants which mimic the complex morphology and structure of bone tissue. Moreover, the presence of the coating completely preserves the in vitro bioactivity of the bioactive glass samples, whose surfaces are converted into hydroxyapatite after a few days of immersion in a simulated body fluid solution (SBF). © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:3251-3258, 2012.
Glasses having a chemical composition between 1Na2O–2CaO–3SiO2 (1N2C3S) and 1.5Na2O–1.5CaO–3SiO2, containing 0, 2, 4 and 6 wt% P2O5, were crystallized to several volume percent through thermal treatments in the range 550–700 °C. These glasses and glass-ceramics were exposed to a simulated body fluid solution (SBF-K9 which is close to human plasma) for several time periods. Fourier transform infrared spectroscopy (FTIR) was used to determine the rate of hydroxy carbonate apatite (HCA) formation. Crystallization decreased the kinetics but did not inhibit the development of a HCA layer, even in fully crystallized ceramics. The onset time for crystallization of HCA varied from 8 h for a glass containing 6% P2O5 to 35 h for a fully crystallized 1.07Na2O–2CaO–3SiO2 ceramic. The HCA layer formation of these compositions in `in vitro' tests is much faster than in commercial bioactive materials such as synthetic hydroxyapatite ceramic, A/W glass-ceramic, Ceravital and Bioverit, for which the onset time usually takes at least seven days. FTIR and inductive coupled plasma studies confirmed the formation of an apatite layer which indicates bioactivity in the 1N2C3S crystal phase. X-ray diffraction experiments show that the phosphorus ions are kept in solid solution in the crystal phase. An apatite-like compound only appeared when the specimens were submitted to very long additional thermal treatments. The bioactivity of commercial materials is based on the apatite crystal phase, while the high level of bioactivity of this new generation of glass-ceramics is attained due to the combination of two mechanisms acting simultaneously; a non-phosphate bioactive crystal phase (1N2C3S) and the phosphorus ions in solid solution which are easily released from the structure, promoting a faster HCA layer formation similar to 45S5 Bioglass®.
Bioglass® 45S5 is widely used in biomedical applications due to its ability to bond to bone and even to soft tissues. The sintering ability of Bioglass® powders is a key factor from a technological point of view, since its govern the production of advanced devices, ranging from highly porous scaffolds to functionalized coatings. Unfortunately this particular glass composition is prone to crystallize at the temperature required for sintering and this may impair the bioactivity of the original glass. For these reasons, a prerequisite to tailor the fabrication of Bioglass®-derived implants is to understand the interaction between sintering, crystallization and bioactivity. In this work the structural transformations which occur during the heat treatment of Bioglass® are reviewed and a special attention is paid to the sintering and crystallization processes. Moreover the bioactivity of the final glass-ceramics is discussed and some alternative glass formulations are reported.
Bioactive-glass-derived scaffolds are crucial in bone tissue engineering since they act as temporary templates for tissue regrowth, providing structural support to the cells in a resulting3Darchitecture. However, manyissues remain open with regard to their design. On the one hand, bioceramic scaffolds should be bioactive, highly porous and should possess adequate mechanical properties; on the other hand, attempts to improve the mechanical properties of the widely used 45S5 Bioglass® turn the bioactive glass itself into a glass-ceramic, with non-trivial effects on the resulting scaffold bioactivity. In this work, for the first time anewbioactive glass compositionwasemployedto produce scaffolds for bone tissue engineering. The new glass composition can be treated at a relatively low temperature and it is characterized by a reduced tendency to crystallize compared to the 45S5 Bioglass®. Moreover, the presented scaffolds are realized with a recently developed technique described here in detail. The resulting samples are highly porous and bioactive. Additionally, they possess a resistant and at the same time permeable surface similar to a shell, which ensures good manageability.
Two innovative glass compositions based on the commonly used 45S5 Bioglass® were developed by increasing the calcium quantity and replacing the sodium oxide with a specific content of potassium oxide. The new glasses, named BG_Ca/K and BG_Ca/Mix, can be prepared using a conventional melting process and show a very low tendency to crystallize. Thanks to this peculiarity, BG_Ca/K and BG_Ca/Mix powders can be sintered at a relatively low temperature (800°C) to obtain samples of high compactness and bioactivity, since their amorphous nature is preserved. Consequently, the proposed glasses are perfect for making specific products such as scaffolds or hydroxyapatite‐based composites. Furthermore, the relatively low alkali amount in the new compositions gives rise to a slow ion leaching in simulated body fluid, thus avoiding abrupt changes in pH that can damage osteoblasts or negatively affect their behavior.
A bioactive glass containing (in wt%) SiO2 48, P2O5 9.5, Na2O 20 and CaO 22.5 was transformed into a glass-ceramic through a heat treatment. The apatite formation on the surface of this glass-ceramic was examined in a simulated physiological solution. The data from X-ray diffraction, infrared reflection spectroscopy, scanning electron microscopy together with energy-dispersive X-ray analysis and composition imaging of backscattered electrons showed that the formation of the surface apatite layer depends on the relative amount of residual glassy phase in the glass-ceramic. The apatite layer was found to formin vitro on its surface if the glass-ceramic contained a residual glassy phase in a relative proportion more than a limiting volume. It lay on a layer rich in silica. However, only, a silica-rich layer was developed within the surface region of the glass-ceramic during the interaction with solution if the glass was almost completely crystallized. It is proposed that the apatite formation on the surface of the glass-ceramic is mainly caused by its residual glass. The residual glass facilitating apatite formation is considered to provide a negatively charged surface developed during its corrosion in the surrounding solution. The negatively charged surface attracts calcium ions and creates a solution within the glass — solution interface that is highly supersaturated with respect to hydroxyapatite. This leads to the formation of apatite on the surface of the glass-ceramic.
The variables affecting the nucleation and crystallization of biological hydroxy carbonate apatite (HCA) on porous gel-silica substrates are examined. Texture is the critical variable with the rate of HCA formation increasing as pore size and pore volume increase, with pore sizes >2 nm required to achieve rapid kinetics (4–6 days) of fully crystallized HCA. The concentration of silanol groups on the silica surface does not control the rate of HCA formation although metastable surface defects, such as trisiloxane rings, may be involved in HCA nucleation.
Since the 1970s, various types of ceramic, glass and glass-ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200°C÷1300°C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass-ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are realized and discussed. The samples can be sintered at a relatively low temperature (800°C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.
A 3D-scaffold for bone tissue engineering should show an interconnected macroporous network with pores exceeding 100μm to favor cell penetration and vascularisation, should be osteoproductive and should exhibit sufficient mechanical strength. In this work, bioactive glass–ceramic scaffold characterised by a network of pores and struts were obtained using the sponge impregnation method. Specifically, 3D-scaffolds with a total porosity of 75vol.% and 2MPa of compressive strength were prepared through a fine tuning of the processing parameters. On the as obtained scaffolds, silver ions were introduced in controlled amount through ion-exchange process imparting antibacterial properties.
The thermal decomposition of sodium nitrate and the effects of several oxides, such as silica, titania, zirconia, alumina, and magnesia, on the decomposition were studied up to 900 degree C by means of the thermal analysis, gas analysis, and chemical analysis of the reaction products. The reaction of sodium nitrate and silica was especially investigated in some detail over a wide composition range. The thermal decomposition of sodium nitrate started at about 450 degree C. The gases formed were O//2, NO, and N//2, the formation of N//2 being detected above 680 degree C.
B-carbonateapatite (CHA) powder was synthesized starting from calcium nitrate tetrahydrate, diammonium hydrogen phosphate and sodium hydrogen carbonate. The powder was fully characterized in terms of phase purity, stoichiometry, morphology, specific surface area and particle size distribution. The thermal stability of the powder in air and CO2 atmosphere also was evaluated by thermal analysis. Electroacoustic analysis of the water based suspension of the CHA powder was used to determine the stability of the slurry. Porous bodies of CHA were prepared by impregnation of cellulose sponges with a proper slurry of the powder and optimizing the subsequent sintering. The fired samples were characterized in terms of phase purity and carbonate content, microstructure and pore size distribution. The compressive strength also was evaluated, resulting in 6.0±0.5 MPa. First results of in vivo tests on New Zealand White rabbits showed good biocompatibility and osteointegration of the CHA implant, with higher osteoconductive properties and earlier bioresorption, compared to HA samples, used as control.
Ceramics used for the repair and re- construction of diseased or damaged parts of the musculo-skeletal sys- tem, termed bioceramics, may be bio- inert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hy- droxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated met- als, alumina). Applications include re- placements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial re- construction, augmentation and stabi- lization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are be- ginning to be understood, which can result in the molecular design of bio- ceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year)
Recently several attempts have been made to combine calcium phosphates, such as β-tricalcium phosphate (β-TCP) and, most of all, hydroxyapatite (HA), with bioactive glasses of different composition, in order to develop composites with improved biological and mechanical performance. Unfortunately, the production of such systems usually implies a high-temperature treatment (up to 1300°C), which may result in several drawbacks, including crystallization of the original glass, decomposition of the calcium phosphate phase and/or reactions between the constituent phases, with non-trivial consequences in terms of microstructure, bioactivity and mechanical properties of the final samples. In the present contribution, novel binary composites have been obtained by sintering a bioactive glass, characterized by a low tendency to crystallize, with the addition of HA or β-TCP as the second phase. In particular, the composites have been treated at a relatively low temperature (818°C and 830°C, depending on the sample), thus preserving the amorphous structure of the glass and minimizing the interaction between the constituent phases. The effects of the glass composition, calcium phosphate nature and processing conditions on the composite microstructure, mechanical properties and in vitro bioactivity have been systematically discussed. To conclude, a feasibility study to obtain scaffolds for bone tissue regeneration has been proposed.
Three-dimensional, highly porous foam-like composite scaffolds were fabricated by coating 45S5 Bioglass-derived glass-ceramic foams with a biodegradable poly-(3-hydroxybutyrate) (PHB) layer. The PHB was produced by bacteria isolation, using a fermentation process. The glass-ceramic scaffolds were fabricated by the replication technique using 45S5 Bioglass powder. The sintering process was optimised in order to increase the mechanical strength of the foam scaffolds. During sintering, the glass crystallises, forming a mixed sodium calcium silicate (Na2Ca2Si3O9) phase. The microstructure of the composite scaffolds was analysed by scanning electron microscopy and x-ray diffraction. The polymer coating did not affect the interconnectivity of the pore structure. The compressive strength of the coated and uncoated scaffolds was measured and it was found that the polymer coating considerably increased the compressive strength of the scaffolds. Bioactivity was studied by soaking the samples in a simulated body fluid (SBF) to assess the formation of hydroxyapatite (HA) crystals on the scaffolds' surfaces. It was found that these novel composite scaffolds are highly bioactive, as after two weeks of immersion in SBF, a uniform layer of HA crystals was formed. The novel Bioglass/PHB composite foams are promising candidates for bone tissue engineering scaffolds.
In the present contribution, the innovative in situ Raman micro-spectroscopy was applied to investigate the in vitro reactivity of various bioactive glasses. All the investigated glasses belonged to the Na(2)O\K(2)O-CaO-P(2)O(5)-SiO(2) system, but contained sensibly different percentages of network modifiers. The glasses were immersed for increasing times, up to 96 h, in simulated body fluid (SBF) and in tris-buffered (TRIS) solution. In this way, two fundamental items were addressed, i.e. the effect of the glass composition and the nature of the soaking fluid on the overall reactivity. As regards the SBF, all the glasses were able to promote the formation of a hydroxyl-carbonate apatite (HCA) surface layer in very short times. The reaction rate was particularly quick for the 45S5 Bioglass (R) and for its potassium-based variant (BioK), however all the glasses could form a continuous HCA layer already after 96 h. The observed difference in reaction kinetics may be due to the glass composition, since the glasses relatively poor in Na ions (BG_Ca) experience slower ion release in the first stages of the HCA formation, while the glasses relatively poor in Ca ions (BG_Na) undergo slower nucleation and growth of HCA. The development of HCA was also observed in TRIS, but the reaction rate was generally slower than in SBF. In fact, while the SBF is a complicated solution supersaturated in apatite, which favours the precipitation of HCA, the TRIS is a simple tris(hydroxymethyl)aminomethane solution in water, which does not provide the ions for the HCA formation. As a consequence, the aforementioned effects due to the glass composition were even more evident in TRIS than in SBF. Nevertheless the TRIS could represent a valuable alternative to the standard SBF whenever a slow reaction rate might be beneficial, such as, for example, in order to better observe the samples evolution.
The kinetics of the thermal decomposition of sodium nitrate and of the reaction between sodium nitrite and oxygen were investigated in the presence of argon and oxygen, at atmospheric pressure, over the temperature range of 600 to 780°. The rate of reaction was followed by observing changes in the volume of the systems as a function of time at constant pressure. Mass spectrometric analyses revealed that the gases formed during the decomposition of sodium nitrate consisted of nitrogen, oxygen and small quantities of nitrogen dioxide. The nitrogen and some of the oxygen were due to the decomposition of sodium nitrite and sodium Superoxide, intermediate products of the decomposition of sodium nitrate. From the investigation of the reaction between sodium nitrite and oxygen it was found that equilibrium was attained between sodium nitrate, sodium nitrite and oxygen below 700°. Above 700° the oxidation reaction was followed by the decomposition of sodium nitrite. Although the reaction velocity increased with temperature, the extent of reaction decreased with increasing temperature. From the temperature dependency of the equilibrium constants, the heat of reaction for the formation of one mole of sodium nitrate from sodium nitrite and oxygen was calculated to be -24.5 kcal, per mole. The rate process for the oxidation reaction appears to be surface dependent, as indicated by the effect of varying the area of contact between gaseous oxygen and the sodium nitrite melt. The kinetics involves a first order reversible reaction with respect to sodium nitrate and sodium nitrite. The energies of activation were determined for the oxidation and decomposition reactions and a reaction mechanism is proposed. The entropies and free energies of activation and the nitrogen to oxygen bond energy in sodium nitrate were also determined.
Because of their excellent bioactivity, bioactive glasses are increasingly diffused to produce biomedical devices for bone prostheses, to face the dysfunctions that may be caused by traumatic events, diseases, or even natural aging. However, several processing routes, such as the production of scaffolds or the deposition of coatings, include a thermal treatment to apply or sinter the glass. The exposure to high temperature may induce a devetrification phenomenon, altering the properties and, in particular, the bioactivity of the glass. The present contribution offers an overview of the thermal behavior and properties of two glasses belonging to the Na2O-CaO-P2O5-SiO2 system, to be compared to the standard 45S5 Bioglass®. The basic goal is to understand the effect of both the original composition and the thermal treatment on the performance of the sintered glasses. The new glasses, the one (BG_Na) with a high content of Na2O, the other (BG_Ca) with a high content of CaO, were fully characterized and sintering tests were performed to define the most interesting firing cycles. The sintered samples, treated at 880°C and 800°C respectively, were investigated from a microstructural point of view and their mechanical properties were compared to those of the bulk (not sintered) glass counterparts. The effect of sintering was especially striking on the BG_Ca material, whose Vickers hardness increased from 598.9 ± 46.7 HV to 1053.4 ± 35.0 HV. The in vitro tests confirmed the ability of the glasses, both in bulk and sintered form, of generating a hydroxyapatite surface layer when immersed in a simulated body fluid. More accurate biological tests performed on the sintered glasses proved the high bioactivity of the CaO-rich composition even after a heat treatment. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2012.
A new tetrazolium salt, XTT, has been synthesized. XTT is reduced by a considerable variety of cell lines to a water-soluble formazan. XTT appears to merit further investigation as a reagent for broader application to cell culture assay systems.
In this study, the synthesis of SiO2–CaO–P2O5–MgO bioactive glass was performed by the sol-gel method. Sol-gel-derived bioglass material was produced both in powder and in discs form by uniaxial pressing, followed by sintering at 700 °C. The obtained material was evaluated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning caloremetry (DSC) analyses. The biocompatibility evaluation of the formed glass was assessed through in vitro cell culture [alkaline phosphatase (AP) activity of osteoblasts] experiments and immersion studies in simulated body fluid (SBF) for different time intervals while monitoring the pH changes and the concentration of calcium, phosphorus and magnesium in the SBF medium. The SEM, XRD and FTIR studies were conducted before and after soaking of the material in SBF. At first, an amorphous calcium phosphate was formed; after 7 days this surface consisted of deposited crystalline apatite. The present investigation also revealed that the sol-gel derived quaternary bioglass system has the ability to support the growth of human fetal osteoblastic cells (hFOB 1.19). Finally, this material proved to be non-toxic and compatible for the proposed work in segmental defects in the goat model in vivo.
Bioactive glass is well known for its ability of bone regeneration, and sol-gel bioactive glass has many advantages compared with melt-derived bioactive glass. 3-D scaffold prepared by the sol-gel method is a promising substrate material for bone tissue engineering and large-scale bone repair. Porous sol-gel glass in the CaO-SiO2-P2O5 system with macropores larger than 100 μm was prepared by the addition of stearic acid as a pore former. The diameter of the pore created by the pore former varied from 100 to 300 μm. The formation of a hydroxyapatite layer on the glass was analyzed by studying the surface of the porous glass by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman spectra after they had been immersed in simulated body fluid (SBF) for some time, and the porous glass shows good bioactivity.
In this work, the 45S5 bioactive glass was synthesized through an aqueous sol-gel method. Characteristic functional groups were evidenced by Fourier transform infrared spectroscopy, the thermal behaviour was investigated by thermogravimetric and differential thermal analysis, crystallization kinetics and phase evolution were followed by X-ray diffraction measurements. The sintering behaviour of the sol-gel derived 45S5 was then studied by dilatometry and the microstructural evolution was followed step-by-step, interrupting the thermal cycle at different temperatures. In vitro dissolution tests were performed in order to assess the degradation behaviour of sol-gel derived 45S5 samples thermally treated at different temperatures. A relevant influence of the calcination conditions (namely, dwelling time and temperature) of the as-prepared powder on the phase appearance and its sintering behaviour as well as on the porosity features, in terms of pore dimension and interconnectivity, of the fired materials was stated.
Cell proliferation, a main target in cancer therapy, is influenced by the surrounding three-dimensional (3D) extracellular matrix (ECM). In vitro drug screening is, thus, optimally performed under conditions in which cells are grown (embedded or trapped) in dense 3D matrices, as these most closely mimic the adhesive and mechanical properties of natural ECM. Measuring cell proliferation under these conditions is, however, technically more challenging compared with two-dimensional (2D) culture and other "3D culture conditions," such as growth on top of a matrix (pseudo-3D) or in spongy scaffolds with large pore sizes. Consequently, such measurements are only slowly applied on a wider scale. To advance this, we report on the equal quality (dynamic range, background, linearity) of measuring the proliferation of cell layers embedded in dense 3D matrices (collagen, Matrigel) compared with cells in 2D culture using the easy (one-step) and in 2D well-validated, 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT)-assay. The comparison stresses the differences in proliferation kinetics and drug sensitivity of matrix-embedded cells versus 2D culture. Using the specific cell-layer-embedded 3D matrix setup, quantitative measurements of cell proliferation and cell invasion are shown to be possible in similar assay conditions, and cytostatic, cytotoxic, and anti-invasive drug effects can thus be reliably determined and compared in physiologically relevant settings. This approach in the 3D matrix holds promise for improving early-stage, high-throughput drug screening, targeting either highly invasive or highly proliferative subpopulations of cancers or both.
Bioactive glass of the type CaO–P2O5–SiO2 was obtained by the sol–gel processing method. The obtained material was characterized by X-ray powder diffraction (XRD). Composite samples of hydroxyapatite with synthesized bioglass were prepared at 1000 °C and characterized by XRD, Fourier transform infrared spectroscopy (FTIR), and surface electron microscopy (SEM). The bioactivity was examined in vitro with respect to the ability of hydroxyapatite layer to form on the surface as a result of contact with simulated body fluid (SBF). XRD, FTIR and SEM studies were conducted before and after contact of the material with SBF. It could be detected that the bioglass was crystallized partly. Furthermore, silicated hydroxyapatite may have formed due to the diffusion of silicate groups to the apatite phase and these may have substituted for the phosphate groups. It can be concluded from SEM and FTIR results that apatite phase formed after 14 days in SBF.
A key issue for bone tissue engineering is the design of bioceramic scaffolds combining high porosity with adequate mechanical properties. Furthermore, a resistant surface is required in order to have manageable samples for both in vivo and in vitro applications. Here a new protocol that aims at giving an appropriate response to these issues is developed. The realized shell scaffolds, obtained by combining a modified replication technique with the usual polymer burning-out method, look rather promising mainly thanks to their manageability, porosity and permeability. In this preliminary work the developed technique is discussed, together with an overview on the structure of the realized samples.
The crystallization kinetics of tape cast bioactive glass 45S5 was studied using non-isothermal methods. XRD confirmed that Na2Ca2Si3O9 was formed during heating up to 1000 °C. The modified Kissinger equation was used to determine that the activation energy for crystallization was 350 kJ/mol. The Avrami exponent, n, was determined to be 0.96 (Ozawa method) and 0.94 (Augis–Bennett method). Such results indicated that the particulate jet milled bioactive glass 45S5 (3 μm average particle size) undergoes surface crystallization during heat treatment. Previous results showed that the porosity of tape cast sintered bioactive glass 45S5 strongly influenced the in vitro bioactivity. Ease of crystallization of tape cast bioactive glass 45S5 suggested that it is fully crystalline prior to undergoing significant densification above 800 °C.
A common characteristic of glasses, glass-ceramics and ceramics that bond to living tissues is the development of a bioactive hydroxyapatite (HA) in vivo at body temperature. Materials with the highest levels of bioactivity develop a silica gel layer that enhances formation of the HA layer. These sol-gel processes are now used to produce bioactive coatings, powders and substrates that offer molecular control over the incorporation and biological behaviour of proteins and cells with broad applications as implants and sensors.
We report on the structural transformations of Bioglass® during thermal treatments. Just after the glassy transition, at 550 °C, a glassy phase separation occurs at 580 °C, with the appearance of one silicate- and one phosphate-rich phase. It is followed by the crystallization of the major phase Na2CaSi2O6, from 610 to 700 °C and of the secondary phase, silico-rhenanite, at 800 °C. The latter evolves from the phosphate-rich glassy phase, which is still present after the first crystallization. In order to control the processing of glass-ceramic products from Bioglass®, crystallization kinetics were studied via differential scanning calorimetry measurements in the range of 620–700 °C and temperature–time–transformation curves were established.
A large part of the scientific community has accepted the paradigm that a simulated body solution (SBF) can be used to test the bioactivity of a material. This is exemplified by the rapidly increasing number of publications using this test. The aim of this document is to demonstrate that (i) there is presently not enough scientific data to support this assumption, and (ii) even though the assumption was valid, the way the test is generally conducted leaves room for improvement. Theoretical arguments and facts supporting these statements are provided, together with possible improvements of the proposed bioactivity test.
A magic angle spinning nuclear magnetic resonance (MAS-NMR) investigation of the environments of 29Si, 31P and 23Na, in glasses from the Na2OCaOSiO2(6 wt% P2O5) system, has shown that the distribution of non-bridging oxygens can be described by a binary distribution of Q2 and Q3 silicon species. The changes in the chemical shifts of these two species with composition are interpreted as resulting from the preferential association of Na+ with Q3 and Ca2+ with Q2. It is suggested that it is this partitioning that determines bioactivity by controlling the dissolution, hydrolysis and condensation reactions which occur at the interface between the glass and the physiological environment.
This paper reviews the discovery that controlled release of biologically active Ca and Si ions from bioactive glasses leads to the up-regulation and activation of seven families of genes in osteoprogenitor cells that give rise to rapid bone regeneration. This finding offers the possibility of creating a new generation of gene activating glasses designed specially for tissue engineering and in situ regeneration of tissues. Recent findings also indicate that controlled release of lower concentrations of ionic dissolution products from bioactive glasses can be used to induce angiogenesis and thereby offer potential for design of gene activating glasses for soft tissue regeneration.
A new protocol, based on a modified replication method, is proposed to obtain bioactive glass scaffolds. The main feature of these samples, named "shell scaffolds", is their external surface that, like a compact and porous shell, provides both high permeability to fluids and mechanical support. In this work, two different scaffolds were prepared using the following slurry components: 59 % water, 29 % 45S5 Bioglass(®) and 12 % polyvinylic binder and 51 % water, 34 % 45S5 Bioglass(®), 10 % polyvinylic binder and 5 % polyethylene. All the proposed samples were characterized by a widespread microporosity and an interconnected macroporosity, with a total porosity of 80 % vol. After immersion in a simulated body fluid (SBF), the scaffolds showed strong ability to develop hydroxyapatite, enhanced by the high specific surface of the porous systems. Moreover preliminary biological evaluations suggested a promising role of the shell scaffolds for applications in bone tissue regeneration. As regards the mechanical behaviour, the shell scaffolds could be easily handled without damages, due to their resistant external surface. More specifically, they possessed suitable mechanical properties for bone regeneration, as proved by compression tests performed before and after immersion in SBF.
In the present work, bioactive powders of the quaternary SiO2–CaO–Na2O–P2O5 system were synthesized by means of a sol–gel route. In their synthesis, tetraethoxysilane (Si(OC2H5)4), calcium nitrate tetrahydrate (Ca(NO3)2∙4H2O) and sodium nitrate (NaNO3) were chosen as precursors of SiO2, CaO and Na2O, respectively. For P2O5, two different precursors were tested: triethylphosphate (OP(OC2H5)3) and phosphoric acid (H3PO4). The gels were then converted into ceramic powders by heat treatments in the temperature range 700–1000°C. The resulting materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) and in vitro bioactivity in acellular simulated body fluid (SBF). During the conversion of the gels into ceramics the mineralization behavior of the two sets of samples was different, but all the resulting materials were bioactive. The samples prepared using phosphoric acid exhibited the best in vitro bioactivity. This result was attributed to the preferential formation of bioactive sodium calcium silicate Na2Ca2Si3O9 crystals, especially in the samples submitted to heat treatments at 700 and 800°C, which could not be observed in the samples prepared using triethylphosphate.
A polymer foam replication technique was used to prepare porous scaffolds of 13-93 bioactive glass with a microstructure similar to that of human trabecular bone. The scaffolds, with a porosity of 85+/-2% and pore size of 100-500 microm, had a compressive strength of 11+/-1 MPa, and an elastic modulus of 3.0+/-0.5 GPa, approximately equal to the highest values reported for human trabecular bone. The strength was also considerably higher than the values reported for polymeric, bioactive glass-ceramic and hydroxyapatite constructs prepared by the same technique and with the equivalent level of porosity. The in vitro bioactivity of the scaffolds was observed by the conversion of the glass surface to a nanostructured hydroxyapatite layer within 7 days in simulated body fluid at 37 degrees C. Protein and MTT assays of in vitro cell cultures showed an excellent ability of the scaffolds to support the proliferation of MC3T3-E1 preosteoblastic cells, both on the surface and in the interior of the porous constructs. Scanning electron microscopy showed cells with a closely adhering, well-spread morphology and a continuous increase in cell density on the scaffolds during 6 days of culture. The results indicate that the 13-93 bioactive glass scaffolds could be applied to bone repair and regeneration.
Although Bioglass® has existed for nearly half a century its ability to trigger bone formation and tuneable degradability is vastly superior to other bioceramics, such as SiO(2)-CaO bioactive glasses. The sol-gel process of producing glass foams is well established for SiO(2)-CaO compositions, but not yet established for 45S5 composites containing Na(2)O. In this work the sol-gel derived 45S5 Bioglass® has for the first time been foamed into highly porous three-dimensional scaffolds using a surfactant, combined with vigorous mechanical stirring and subsequent sintering at 1000°C for 2 h. It was found that the mechanical strength of the sintered sol-gel derived Bioglass® scaffolds was significantly improved, attributable to the small fraction of material on the pore walls. More importantly, the compressive strength of the three-dimensional scaffolds produced by this surfactant foaming method could be predicted using Gibson and Ashby's closed cell model of porous networks. A comparative experiment revealed that ion release from the sol-gel derived Bioglass® foams was faster than that of counterparts produced by the replication technique. In vitro evaluation using osteoblast-like cells demonstrated that the sol-gel derived 45S5 Bioglass foams supported the proliferation of viable cell populations on the surface of the scaffolds, although few cells were observed to migrate into the virtually closed pores within the foams. Further work should be focused on modifications of the reaction conditions or alternative foaming techniques to improve pore interconnection.
The high-velocity suspension flame spraying technique (HVSFS) was employed in order to deposit 45S5 bioactive glass coatings onto titanium substrates, using a suspension of micron-sized glass powders dispersed in a water + isopropanol mixture as feedstock. By modifying the process parameters, five coatings with different thickness and porosity were obtained. The coatings were entirely glassy but exhibited a through-thickness microstructural gradient, as the deposition mechanisms of the glass droplets changed at every torch cycle because of the increase in the system temperature during spraying. After soaking in simulated body fluid, all of the coatings were soon covered by a layer of hydroxyapatite; furthermore, the coatings exhibited no cytotoxicity and human osteosarcoma cells could adhere and proliferate well onto their surfaces. HVSFS-deposited 45S5 bioglass coatings are therefore highly bioactive and have potentials as replacement of conventional hydroxyapatite in order to favour osseointegration of dental and prosthetic implants.
Several inorganic materials such as special compositions of silicate glasses, glass-ceramics and calcium phosphates have been shown to be bioactive and resorbable and to exhibit appropriate mechanical properties which make them suitable for bone tissue engineering applications. However, the exact mechanism of interaction between the ionic dissolution products of such inorganic materials and human cells are not fully understood, which has prompted considerable research work in the biomaterials community during the last decade. This review comprehensively covers literature reports which have investigated specifically the effect of dissolution products of silicate bioactive glasses and glass-ceramics in relation to osteogenesis and angiogenesis. Particularly, recent advances made in fabricating dense biomaterials and scaffolds doped with trace elements (e.g. Zn, Sr, Mg, and Cu) and investigations on the effect of these elements on the scaffold biological performance are summarized and discussed in detail. Clearly, the biological response to artificial materials depends on many parameters such as chemical composition, topography, porosity and grain size. This review, however, focuses only on the ion release kinetics of the materials and the specific effect of the released ionic dissolution products on human cell behaviour, providing also a scope for future investigations and identifying specific research needs to advance the field. The biological performance of pure and doped silicate glasses, phosphate based glasses with novel specific compositions as well as several other silicate based compounds are discussed in detail. Cells investigated in the reviewed articles include human osteoblastic and osteoclastic cells as well as endothelial cells and stem cells.
The sol-gel process of producing SiO(2)-CaO bioactive glasses is well established, but problems remain with the poor mechanical properties of the amorphous form and the bioinertness of its crystalline counterpart. These properties may be improved by incorporating Na(2)O into bioactive glasses, which can result in the formation of a hard yet biodegradable crystalline phase from bioactive glasses when sintered. However, production of Na(2)O-containing bioactive glasses by sol-gel methods has proved to be difficult. This work reports a new sol-gel process for the production of Na(2)O-containing bioactive glass ceramics, potentially enabling their use as medical implantation materials. Fine powders of 45S5 (a Na(2)O-containing composition) glass ceramic have for the first time been successfully synthesized using the sol-gel technique in aqueous solution under ambient conditions, with the mean particle size being approximately 5 microm. A comparative study of sol-gel derived S70C30 (a Na(2)O-free composition) and 45S5 glass ceramic materials revealed that the latter possesses a number of features desirable in biomaterials used for bone tissue engineering, including (i) the crystalline phase Na(2)Ca(2)Si(3)O(9) that couples good mechanical strength with satisfactory biodegradability, (ii) formation of hydroxyapatite, which may promote good bone bonding and (iii) cytocompatibility. In contrast, the sol-gel derived S70C30 glass ceramic consisted of a virtually inert crystalline phase CaSiO(3). Moreover, amorphous S70C30 largely transited to CaCO(3) with minor hydroxyapatite when immersed in simulated body fluid under standard tissue culture conditions. In conclusion, sol-gel derived Na(2)O-containing glass ceramics have significant advantages over related Na(2)O-free materials, having a greatly improved combination of mechanical capability and biological absorbability.
This research work is focused on the preparation of macroporous glass-ceramic scaffolds with high mechanical strength, equivalent with cancellous bone. The scaffolds were prepared using an open-cells polyurethane sponge as a template and glass powders belonging to the system SiO(2)-P(2)O(5)-CaO-MgO-Na(2)O-K(2)O. The glass, named as CEL2, was synthesized by a conventional melting-quenching route, ground and sieved to obtain powders of specific size. A slurry of CEL2 powders, polyvinyl alcohol (PVA) as a binder and water was prepared in order to coat, by a process of impregnation, the polymeric template. A thermal treatment was then used to remove the sponge and to sinter the glass powders, in order to obtain a replica of the template structure. The scaffolds were characterized by means of X-ray diffraction analysis, morphological observations, density measurements, volumetric shrinkage, image analysis, capillarity tests, mechanical tests and in vitro bioactivity evaluation.
It has been proposed that the formation of a surface apatite layer in vivo on surface active ceramics is an essential condition for chemical bonding between ceramics and bone tissue. To clarify the difference in bone-bonding mechanisms between surface active ceramics and bioresorbable ceramics, two experiments were performed using plates of dense beta-tricalcium phosphate (beta-TCP). First, plates of beta-TCP were implanted subcutaneously in rats for 8 weeks. Surface change due to bioresorption was observed with scanning electron microscopy. Formation of the apatite layer on the surface was investigated using thin-film x-ray diffraction and Fourier transform infrared reflection spectroscopy. Second, plates of beta-TCP were implanted in tibiae of rabbits for 8 and 25 weeks and subjected to the detaching test to measure bone-bonding strength. beta-TCP bonded strongly to bone. Undecalcified sections of the interface of bone and beta-TCP were examined with SEM-EPMA. However, by physicochemical methods, no formation of surface apatite layer was observed. These results suggest that beta-TCP bonds to bone through microanchoring between bone and rough surface of resorbed beta-TCP.
A new tetrazolium salt XTT, sodium 3'-[1-[(phenylamino)-carbonyl]-3,4-tetrazolium]-bis(4-methoxy-6- nitro)benzene-sulfonic acid hydrate, was evaluated for use in a colorimetric assay for cell viability and proliferation by normal activated T cells and several cytokine dependent cell lines. Cleavage of XTT by dehydrogenase enzymes of metabolically active cells yields a highly colored formazan product which is water soluble. This feature obviates the need for formazan crystal solubilization prior to absorbance measurements, as required when using other tetrazolium salts such as MTT. Bioreduction of XTT by all the murine cells examined was not particularly efficient, but could be potentiated by addition of electron coupling agents such as phenazine methosulfate (PMS) or menadione (MEN). Optimal concentrations of PMS or MEN were determined for the metabolism of XTT by the T cell lines HT-2 and 11.6, NFS-60 a myeloid leukemia, MC/9 a mast cell line and mitogen activated splenic T cells. When used in combination with PMS, each of these cells generated higher formazan absorbance values with XTT than were observed with MTT. Thus the use of XTT in colorimetric proliferation assays offer significant advantages over MTT, resulting from reduced assay time and sample handling, while offering equivalent sensitivity.
High-strength bioactive glass-ceramic A-W was soaked in various acellular aqueous solutions different in ion concentrations and pH. After soaking for 7 and 30 days, surface structural changes of the glass-ceramic were investigated by means of Fourier transform infrared reflection spectroscopy, thin-film x-ray diffraction, and scanning electronmicroscopic observations, in comparison with in vivo surface structural changes. So-called Tris buffer solution, pure water buffered with trishydroxymethyl-aminomethane, which had been used by various workers as a "simulated body fluid," did not reproduce the in vivo surface structural changes, i.e., apatite formation on the surface. A solution, ion concentrations and pH of which are almost equal to those of the human blood plasma--i.e., Na+ 142.0, K+ 5.0, Mg2+ 1.5, Ca2+ 2.5, Cl- 148.8, HCO3- 4.2 and PO4(2-) 1.0 mM and buffered at pH 7.25 with the trishydroxymethyl-aminomethane--most precisely reproduced in vivo surface structure change. This shows that careful selection of simulated body fluid is required for in vitro experiments. The results also support the concept that the apatite phase on the surface of glass-ceramic A-W is formed by a chemical reaction of the glass-ceramic with the Ca2+, HPO4(2-), and OH- ions in the body fluid.
Microculture tetrazolium assays are being widely exploited to investigate the mechanisms of both cell activation and cell damage. They are colorimetric assays which are based upon the bioreduction of a tetrazolium salt to an intensely coloured formazan. We contrast the responses obtainable with two new tetrazolium salts, MTS and XTT, when used on the rat lymphoma cell line (Nb2 cells), which has been activated by human growth hormone. These tetrazolium salts, unlike the more commonly used MTT, form soluble formazans upon bioreduction by the activated cells. This has the advantage that it eliminates the error-prone solubilisation step which is required for the microculture tetrazolium assays which employ MTT. Bioreduction of XTT and MTS usually requires addition of an intermediate electron acceptor, phenazine methosulphate (PMS). We found that the XTT/PMS, but not the MTS/PMS, reagent mixture was unstable. Nucleation and crystal formation in the XTT/PMS reagent mixture, prepared in DPBS, could occur within 1-3 min. This resulted in a decline in XTT-formazan production and manifested itself in the microculture tetrazolium assay as both poor within-assay precision and serious assay drift. Several features of the system suggested that the formation of charge-transfer complexes between XTT and PMS accounted for this instability. No such instability was encountered when MTS and PMS were mixed. We demonstrate that MTS/PMS provides microculture tetrazolium assays for hGH which are free from these serious artefacts and which are uniquely precise. In conclusion we therefore advocate the use of MTS in preference to XTT for the new generation of microculture tetrazolium assays.
In order to understand how biomaterials influence bone formation in vivo, it is necessary to examine cellular response to materials in the context of wound healing. Four interrelated properties of biomaterials (chemical composition, surface energy, surface roughness, and surface topography) affect mesenchymal cells in vitro. Attachment, proliferation, metabolism, matrix synthesis, and differentiation of osteoblast-like cell lines and primary chondrocytes are sensitive to one or more of these properties. The nature of the response depends on cell maturation state. Rarely do differentiated osteoblasts or chondrocytes see a material prior to its modification by biological fluids, immune cells and less differentiated mesenchymal cells in vivo. Studies using the rat marrow ablation model of endosteal wound healing indicate that ability of osteoblasts to synthesize and calcify their extracellular matrix is affected by the local presence of the material. Changes in the morphology and biochemistry of matrix vesicles, extracellular organelles associated with matrix maturation and calcification, seen in normal endosteal healing, are altered by implants. Moreover, the material exerts a systemic effect on endosteal healing as well. This may be due to local effects on growth factor production and secretion into the circulation, as well as to the fact that the implant may serve as a bioreactor.