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Formation of a bioactive graded surface structure on Ti-I5Mo-5Zr-3-Al alloy by chemical treatment
Abstract
Simple NaOH and heat treatments provided a Ti-15Mo-5Zr-3Al alloy with a bioactive graded surface structure of an amorphous sodium titanate, where the sodium titanate on the top surface gradually changed into the alloy substrate through titanium oxide. The sodium titanate was free of alloying species of Mo, Zr and Al, since almost all of them were released from the surface of alloy during the first NaOH treatment. The sodium titanate transformed into a hydrated titania via Na+ ion release to induce a bone-like apatite formation on the alloy substrate in a simulated body fluid (SBF). The alloying species neither were released into the SBF nor affected the apatite formation. In the process of apatite formation, the graded surface structure developed into one where the apatite on the top surface gradually changed into the alloy composition through hydrated titania and titanium oxide. It is expected that this graded structure will lead to a strong interfacial bonding strength between the apatite layer and the alloy substrate, thereby providing a tight integration of the alloy with living bone through the apatite layer.
... Because Na + is present in TiO 2 nanotubes and exists in the form of amorphous sodium titanate after alkali treatment [20], the Na ion concentration was increased (PNA). Since the heat treatment did not cause a significant impact on the components of the surface of specimens but it caused a stronger bond between Ti and O [16,[21][22][23][24], the heat-treated group (PNAH) showed similar amount of surface components as the PNA group and had more dense layer (Table 2 and Fig. 1(g)). ...
... Amorphous calcium phosphate is formed on these surfaces by binding with PO 4 2− , and the crystalline structure of calcium phosphate was gradually transformed as: DCP-OCP-TCP-HAp. Finally, a bone-like substance called hydroxyapatite (HAp) can be obtained [16,21,22,30]. ...
... It also displays an osseoconductivity: HA bond to and integrate with living bone spontaneously by forming a biologically active bone-like apatite layer on their surfaces in the body. 5 Therefore, this is especially useful for the fabrication of dental implants where rapid healing is required. 1 Despite its excellent properties as a biomaterial, the inherent mechanical properties of HA-specifically, brittleness, poor tensile strength, and poor impact resistance-restricted its application in many load-bearing situations. 1 In order to overcome the weak points of HA, the concept of applying HA onto metallic implants has been developed. ...
... In this process, the graded surface structure develops into one where the apatite on the top surface gradually changes into alloy substrate through hydrated titania and titanium oxide. 5 Wang et al, suggested that the bioactivity of titania gels depends on the gel' s structure. including crystallographic and porous structure as well as a negative surface charge density. ...
Statement of problem. Hydroxyapatite(HA) coated titanium surfaces have not yet showed the reliable osseointegration in various conditions. Purpose. This study was aimed to investigate microstructures, chemical composition, and surface roughness of the surface coated by the hydrothermal method and to evaluate the effect of hydrothermal coating on the cell attachment, as well as cell proliferation. Material and Methods. Commercially pure(c.p.) titanium discs were used as substrates. The HA coating on c.p. titanium discs by hydrothermal method was performed in 0.12M HCl solu-tion mixed with HA(group I) and 0.1M NaOH solution mixed with HA(group II). GroupⅠ was heated at 180℃ for 24, 48, and 72 hours. GroupⅡ was heated at 180℃ for 12, 24, and 36 hours. And the treated surfaces were evaluated by Scanning electron microscopy(SEM), Energy dis-persive X-ray spectroscopy(EDS), X-ray photoelectron spectroscopy(XPS), X-ray diffraction method(XRD), Confocal laser scanning microscopy(CLSM). And SEM of fibroblast and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide(MTT) assay were used for cellular respons-es of the treated surfaces. Results. The color of surface changed in both groups after the hydrothermal process. SEM images showed that coating pattern was homogeneous in group II, while inhomogeneous in group I. H72 had rosette-like precipitates. The crystalline structure grew gradually in group II, according to extending treatment period. The long needle-like crystals were prominent in N36. Calcium(Ca) and phosphorus(P) were not detected in H24 and H48 in EDS. In all spec-imens of group II and H72, Ca was found. Ca and P were identified in all treated groups through the analysis of XPS, but they were amorphous. Surface roughness did not increase in both groups after hydrothermal treatment. The values of surface roughness were not significantly differ-ent between groups I and II. According to the SEM images of fibroblasts, cell attachments were oriented and spread well in both treated groups, while they were not in the control group. However, no substantial amount of difference was found between groups I and II. Conclusions. In this study during the hydrothermal process procedure, coating character-istics, including the HA precipitates, crystal growth, and crystalline phases, were more satisfactory in NaOH treated group than in HCl treated group. Still, the biological responses of the modified surface by this method were not fully understood for the two tested groups did not differ significantly. Therefore, more continuous research on the relationship between the sur-face features and cellular responses seems to be in need.
... A. New Attempt for the Development of Single Crystalline b-Ti Alloys Implant RECENTLY, some b-type Ti alloys with a bodycentered cubic (bcc) lattice have attracted considerable attention as hard tissue replacements such as artificial hip joints and dental implants. [1][2][3][4][5][6] This is because of their outstanding mechanical properties such as high specific strength, good deformability, and excellent biocompatibility. In addition, their low Young's moduli is focused strongly, which is essential to prevent bone degradation and the absorption caused by the difference of the Young's moduli between the replacement and natural human bone (the so-called stress-shielding effect). ...
... For the development of this single crystalline b-Ti implant, in this study, we focused on the mechanical properties of the Ti-15Mo-5Zr-3Al (wt pct) alloy, which is one of the most promising candidates for application as a biomedical implant b-type Ti alloy. [5,6] In fact, the practical use of this alloy as a biomaterial was approved by the International Organization for Standardization in 2007. ...
Aligned, unidirectional, elongated pores were incorporated in Ti-6Al-4V products fabricated by electron beam melting in order to control the mechanical properties of the products such that they became suitable for biomedical applications. Unidirectional pores were successfully produced when the scan spacing of the electron beam was greater than the diameter of the beam. By changing the scan spacing of the electron beam, the size of the unidirectional pores could be varied. As a result, both the Young’s moduli and the yield stresses of the products with unidirectional pores decreased linearly with an increase in their porosity, owing to the stress concentration coefficient being 1 in the equation representing the relation between strength and porosity for porous materials. Further, low (<35 GPa) Young’s moduli were obtained when the scan spacing was 1 mm or higher, with these values being were close to the typical Young’s modulus of human cortical bone. This suggested that these porous materials could be used to fabricate customized bone implants that exhibited desired mechanical properties and suppressed the stress shielding of bone that is normally noticed when implants made of Ti alloys are used.
... A. New Attempt for the Development of Single Crystalline b-Ti Alloys Implant RECENTLY, some b-type Ti alloys with a bodycentered cubic (bcc) lattice have attracted considerable attention as hard tissue replacements such as artificial hip joints and dental implants. [1][2][3][4][5][6] This is because of their outstanding mechanical properties such as high specific strength, good deformability, and excellent biocompatibility. In addition, their low Young's moduli is focused strongly, which is essential to prevent bone degradation and the absorption caused by the difference of the Young's moduli between the replacement and natural human bone (the so-called stress-shielding effect). ...
... For the development of this single crystalline b-Ti implant, in this study, we focused on the mechanical properties of the Ti-15Mo-5Zr-3Al (wt pct) alloy, which is one of the most promising candidates for application as a biomedical implant b-type Ti alloy. [5,6] In fact, the practical use of this alloy as a biomaterial was approved by the International Organization for Standardization in 2007. ...
The plastic deformation behavior of a β-type Ti-15Mo-5Zr-3Al alloy with a body-centered cubic (bcc) structure, which is a promising material for biomedical applications, was investigated. The orientation dependence of the plastic deformation behavior was examined by using a single crystal. In addition, changes in the mechanical properties depending on the microstructure were examined. The β single phase was maintained even after short-time annealing below 673 K (400 °C). Thus, the variations in the mechanical properties were small. However, an ellipsoidal ω phase and a lath-like α phase were precipitated in long-time annealing at 573 K (300 °C) and 673 K (400 °C), leading to large increases in the yield stress. For the deformation behavior, a dislocation with a Burgers vector parallel to
$ \left\langle {111} \right\rangle $
was observed irrespective of the heat-treatment conditions and loading orientations. However, the observed slip plane changed considerably depending on the loading axis, and the yield stress exhibited a strong orientation dependence because of the dislocation core structure effect in the bcc-structured crystals. The physical properties of Mo, which is the main constituent atom in the current alloy, may strongly affect the dislocation core structure and induce the characteristic orientation dependence of the plastic behavior.
... After being solutionized and aged at different temperatures, the Ti-1553 alloy can achieve a combination of high strength and moderate ductility [7,8]. Moreover, it is considered to be a promising β-Ti alloy for biomedical implants because of its superior mechanical strength [9]. ...
Dissimilar brazing of Ti–15Mo–5Zr–3Al (Ti-1553) to commercially pure titanium (CP-Ti) using Ti–15Cu–15Ni foil was performed in this work. The microstructures in different sites of the brazed joint showed distinct morphologies, which resulted from the distributions of Mo, Cu, and Ni. In the brazed zone adhered to the Ti-1553 substrate, the partitioning of Mo from the Ti-1553 into the molten braze caused the formation of stabilized β-Ti without Ti2Cu/Ti2Ni precipitates. In the CP-Ti side, the brazed joint displayed a predominantly lamellar structure, composed of the elongated primary α-Ti and β-transformed eutectoid. The decrease in the Mo concentration in the brazed zone caused the eutectoid transformation of β-Ti to Ti2Cu + α-Ti in that zone. The diffusion of Cu and Ni from the molten braze into the CP-Ti accounted for the precipitation of Ti2Cu/Ti2Ni in the transformed zone therein. The variation in the shear strength of the joints was related to the amount and distribution of brittle Ti2Ni compounds. Prolonging the brazing time, the wider transformed zone, consisting of coarse elongated CP-Ti interspersed with sparse Ti2Ni precipitates, was responsible for the improved shear strength of the joint.
... As a result, additional surgical efforts are often necessary to fix the issue [2] and may involve revision surgeries with high complication rates and high technical demands [3], they are expensive [4] and have usually a low level of satisfaction for the patients [5]. Besides, Ti-Al-V [6,7], Ti-Mo-Zr-Al [8], Co-Cr-Mo [9,10] and porous Ta [11,12] implants possess also very good bio-and cell compatibility [6] and are used in a large variety of implant applications, i.e., as hip, shoulder or dental implants. But even these implant "workhorses" may promote inflammation and fibrous tissue reactions due to metal ion release. ...
Ceramics are widely used as implant materials; however, they are brittle and may emit particles when used in these applications. To overcome this disadvantage, alumina foams, which represent a 3D cellular structure comparable to that of human trabecular bone structures, were sputter coated with platinum, tantalum or titanium and modified with fibronectin or collagen type I, components of the extracellular matrix (ECM). To proof the cell material interaction, the unmodified and modified materials were cultured with (a) mesenchymal stem cells being a perfect indicator for biocompatibility and releasing important cytokines of the stem cell niche and (b) with fibroblasts characterized as mediators of inflammation and therefore an important cellular component of the foreign body reaction and inflammation after implantation. To optimize and compare the influence of metal surfaces on cellular behavior, planar glass substrates have been used. Identified biocompatible metal surface of platinum, titanium and tantalum were sputtered on ceramic foams modified with the above-mentioned ECM components to investigate cellular behavior in a 3D environment. The cellular alumina support was characterized with respect to its cellular/porous structure and niche accessibility and coating thickness of the refractory metals; the average cell size was 2.3 mm, the average size of the cell windows was 1.8 mm, and the total foam porosity was 91.4%. The Pt, Ti and Ta coatings were completely dense covering the entire alumina foam surface. The metals titanium and tantalum were colonized very well by the stem cells without a coating of ECM components, whereas the fibroblasts preferred components of the ECM on the alumina foam surface.
... SEM imaging of NB/NH and B/300 NaTC samples ( Figure 6:1C and Figure 6:2C, respectively) revealed the characteristic nanoporous structure of sodium titanate expected from the chemical treatment used [514]. Successful conversion of the Ti sputtered surface to sodium titanate was supported by EDX ( Table 6:2) and XPS analysis ( Figure 6:5 & Table 6:4), both confirming the presence of Na-O. ...
Titanate structures have been of interest in many sectors, including healthcare, due to their ease of manufacture (low processing temperature and simplistic equipment), ion exchange potential to produce multifunctional (bioactive and antibacterial) surfaces, as well as their nanoporosity. However, their use has been limited to only Ti-containing materials due to the specific wet chemical methodology employed. The work presented in this thesis demonstrates one of the first studies to generate gallium-doped titanate structures as a multifunctional surface, specifically to assess their cytocompatibility and antibacterial potential for biomedical applications. Successive wet chemical (5 M NaOH; 60 oC; 24 h), ion exchange (4 mM Ga(NO3)3; 60 oC; 24 h), and heat treatment (700 oC; 1 h) stages were employed on Cp-Ti surfaces. Gallium was shown to be fully incorporated (ca. 9 at.%) into the nanoporous titanate structure, and completely replaced sodium (initial Na content ca. 3 at.%). The heat treatment stage crystallised the amorphous titanate layer, which increased the stability and reduced the maximum level of Ga3+ released (ca. 2.76 vs. 0.68 ppm for pre- and post-heat treated gallium titanate samples, respectively) into DMEM over 7 d. Finally, the heat-treated gallium titanate samples were shown to be cytocompatible, compared to the non-heat-treated samples, which demonstrated a significant (p < 0.0001) reduction compared to the TCP control. Unfortunately, neither gallium titanate samples exhibited robust antibacterial properties against S. aureus. The applicability of titanate structures was furthered in this thesis through the optimisation and characterisation of novel wet chemical (5 M NaOH; 60 oC; 24 h) titanate-converted Ti thin films deposited via DC magnetron sputtering. The films produced were deposited onto 316L SS to function as thin coatings for orthopaedic applications. This was in lieu of the ‘gold standard’ plasma sprayed hydroxyapatite (HA) coatings, due to their inherent shortfalls such as residual internal stresses and long-term delamination. An understanding of the titanate growth mechanism through thickness and oxygen variations was also detailed. Tailorable coating properties (structural, morphological, etc.) were achieved via modification of the sputtering parameters used (target power, substrate biasing, and in situ substrate heating). Graded coating structures from columnar (Tc for the α-Ti (002) plane = 3.39) to more equiaxed (Tc(002) = 1.54) coatings were produced, with their influence on titanate formation being investigated. Equiaxed coatings generated the thickest titanate structures (ca. 1.63 vs. 1.12 μm for columnar grown films) due to a reduction in oblique angle crystal growth because of the decreased surface roughness (Ra: ca. 32.6 vs. 26 nm). This was contrary to the hypothesis that more columnar structures would allow greater NaOH penetration, and hence further conversion. It was also found the titanate structures formed even on 50 nm thick Ti films, as well as oxygen limiting the titanate formation mechanism. Finally, sodium and calcium titanate-converted thin (ca. 500 nm) Ti coatings (both columnar and equiaxed) were applied to Mg substrates to tailor its corrosion resistance for biomedical applications. The columnar calcium titanate coatings performed the best of all the coatings tested compared to Mg in terms of their corrosion resistance (Ecorr = ca. -1.33 vs. -1.49 V; icorr = ca. 0.06 vs. 0.31 mA.cm-2, respectively). The novel method outlined in this thesis has demonstrated consistent production of tailorable nanoporous titanate structures on non-Ti containing materials. Furthermore, the produced titanate structures enabled ion substitution of Ca ions, which have previously only been achieved in titanate structures produced on Ti substrates. The results detailed not only enhances the understanding of the titanate growth mechanism, but also demonstrates the broad applications enabled through this platform technology.
... SEM imaging of NB/NH and B/300 NaTC samples ( Figure 6:1C and Figure 6:2C, respectively) revealed the characteristic nanoporous structure of sodium titanate expected from the chemical treatment used [514]. Successful conversion of the Ti sputtered surface to sodium titanate was supported by EDX ( Table 6:2) and XPS analysis ( Figure 6:5 & Table 6:4), both confirming the presence of Na-O. ...
Titanate structures have been of interest in many sectors, including healthcare, due to their ease of manufacture (low processing temperature and simplistic equipment), ion exchange potential to produce multifunctional (bioactive and antibacterial) surfaces, as well as their nanoporosity. However, their use has been limited to only Ti-containing materials due to the specific wet chemical methodology employed.
The work presented in this thesis demonstrates one of the first studies to generate gallium-doped titanate structures as a multifunctional surface, specifically to assess their cytocompatibility and antibacterial potential for biomedical applications. Successive wet chemical (5 M NaOH; 60 oC; 24 h), ion exchange (4 mM Ga(NO3)3; 60 oC; 24 h), and heat treatment (700 oC; 1 h) stages were employed on Cp-Ti surfaces. Gallium was shown to be fully incorporated (ca. 9 at.%) into the nanoporous titanate structure, and completely replaced sodium (initial Na content ca. 3 at.%). The heat treatment stage crystallised the amorphous titanate layer, which increased the stability and reduced the maximum level of Ga3+ released (ca. 2.76 vs. 0.68 ppm for pre- and post-heat treated gallium titanate samples, respectively) into DMEM over 7 d. Finally, the heat-treated gallium titanate samples were shown to be cytocompatible, compared to the non-heat-treated samples, which demonstrated a significant (p < 0.0001) reduction compared to the TCP control. Unfortunately, neither gallium titanate samples exhibited robust antibacterial properties against S. aureus.
The applicability of titanate structures was furthered in this thesis through the optimisation and characterisation of novel wet chemical (5 M NaOH; 60 oC; 24 h) titanate-converted Ti thin films deposited via DC magnetron sputtering. The films produced were deposited onto 316L SS to function as thin coatings for orthopaedic applications. This was in lieu of the ‘gold standard’ plasma sprayed hydroxyapatite (HA) coatings, due to their inherent shortfalls such as residual internal stresses and long-term delamination. An understanding of the titanate growth mechanism through thickness and oxygen variations was also detailed.
Tailorable coating properties (structural, morphological, etc.) were achieved via modification of the sputtering parameters used (target power, substrate biasing, and in situ substrate heating). Graded coating structures from columnar (Tc for the α-Ti (002) plane = 3.39) to more equiaxed (Tc(002) = 1.54) coatings were produced, with their influence on titanate formation being investigated. Equiaxed coatings generated the thickest titanate structures (ca. 1.63 vs. 1.12 μm for columnar grown films) due to a reduction in oblique angle crystal growth because of the decreased surface roughness (Ra: ca. 32.6 vs. 26 nm). This was contrary to the hypothesis that more columnar structures would allow greater NaOH penetration, and hence further conversion. It was also found the titanate structures formed even on 50 nm thick Ti films, as well as oxygen limiting the titanate formation mechanism.
Finally, sodium and calcium titanate-converted thin (ca. 500 nm) Ti coatings (both columnar and equiaxed) were applied to Mg substrates to tailor its corrosion resistance for biomedical applications. The columnar calcium titanate coatings performed the best of all the coatings tested compared to Mg in terms of their corrosion resistance (Ecorr = ca. -1.33 vs. -1.49 V; icorr = ca. 0.06 vs. 0.31 mA.cm-2, respectively).
The novel method outlined in this thesis has demonstrated consistent production of tailorable nanoporous titanate structures on non-Ti containing materials. Furthermore, the produced titanate structures enabled ion substitution of Ca ions, which have previously only been achieved in titanate structures produced on Ti substrates. The results detailed not only enhances the understanding of the titanate growth mechanism, but also demonstrates the broad applications enabled through this platform technology.
... SEM imaging of NB/NH and B/300 NaTC samples ( Figs. 1 C and 2 C) revealed the characteristic nano-porous structure of sodium titanate expected from the chemical treatment used [40] . Successful conversion of the Ti sputtered surface to sodium titanate was supported by EDX ( Table 3 ) and XPS analysis ( Fig. 5 and Table 5 ), both confirming the presence of Na-O. ...
A novel approach was developed to reduce the corrosion rate of magnesium (Mg) metal, utilising titanate coatings. Magnetron sputtering was used to deposit ca. 500 nm titanium (Ti) coatings onto pure Mg discs, followed by hydrothermal conversion and ion exchange reactions to produce sodium and calcium titanate coatings. SEM confirmed the characteristic nanoporous structure of sodium and calcium titanate, with thicknesses ranging from ca. 0.8 to 1.4 µm. XPS analysis confirmed the presence of Ti⁴⁺—O, Na—O, and Ca—O bonding, whilst Raman spectroscopy demonstrated characteristic vibrational modes (such as TiO6 octahedral vibrations) of the sodium and calcium titanate perovskite structure. Furthermore, corrosion studies through potentiodynamic polarisation measurements demonstrated the NB/NH CaTC samples to be superior in reducing Mg degradation, compared to other samples tested, through an increase in Ecorr from −1.49 to −1.33 V, and the reduction in corrosion current density, icorr, from 0.31 to 0.06 mA/cm² for Mg and NB/NH CaTC samples, respectively. There was a clear trend noted for the NB/NH samples, which showed an increase in Ecorr to more positive values in the following order: Mg < Ti coated < NaTC < CaTC. These nanoporous titanate coatings have potential to be applied onto degradable plates for bone fracture fixation, or other orthopaedic applications.
... Ti−OH groups were formed on the titanium surface during the HTT process by the hydrolysis. These groups initiate HAp nucleation according to reactions 7 and 8 mentioned above, resulting in deficiency of Ca and P. 43,44 In order to compensate for the deficiency, these compounds diffuse toward the surface from the inner layer. Thus, the HTT process leads to a high content of Ca and P on the surface. ...
... The osseointegration efficiency, which represents the direct contact between the newly formed bone and the implant, also reflects the biocompatibility and other functions of the implant interface; therefore, an integrated bone-implant interface could facilitate long-term sustained osteogenesis. 28,44,45 We used fluorescence labelling and undecalcified histological analysis to evaluate the osseointegration inside implants at the defects of the radius. The morphological changes in osteointegration between newly formed bones and implant trabeculae on the transverse sections stained with Van Gieson are shown in Fig. 6A. ...
Bone grafting remains the method of choice for the majority of surgeons in the treatment of large bone defects, since it fills spaces and provides support to enhance biological bone repair. Recently, we reported our research on a bioactive multiphase macroporous scaffold with interconnected porous structure, nano-crystal surface microstructure that can release bioactive ions. Moreover, we demonstrated the excellent in vitro biological activity of the scaffold. With this study, we set out to evaluate the in vivo, osteogenesis and vascularization of the scaffold in the treatment of large bone defects (10-mm radial bone defect in rabbits). In comparison with the control group, X-ray and Micro-CT results at the 4th and 8th week post-surgery the bioactive scaffold displayed an enhanced level of new bone and vessel formation. Histological results at the same weeks indicated improved bone formation, osseointegration and new vessel ingrowth inside the bioactive scaffold. These findings establish a good foundation for the potential clinical validation of the bioactive macroporous biomaterial scaffold for use as a bone substitute or in tissue engineering.
... If an alkali-treated specimen is soaked in a SBF solution, Na + on the surface and H 3 O + in the SBF solution are substituted to form the Ti-OH group, and if left to react further with the SBF solution, it binds with Ca + to form calcium titanate. Such a surface induces binding with PO 4 2− , thereby forming amorphous calcium phosphate, which then grows in the order of DCP-OCP-TCP-HAp [14,23,35]. As such, the higher the hydrophilicity of the surface, the greater the HAp induction through the enhanced surface-SBF contact. ...
The aim of this study is to enhance the bioactivity of pure titanium using multiple surface treatments for the application of the implant. To form the biofunctional multilayer coating on pure titanium, anodization was conducted to make titanium dioxide nanotubes, then multi-walled carbon nanotubes were coated using a dipping method after an alkali treatment. The surface characteristics at each step were analyzed using a field emission scanning electron microscope and X-ray diffractometer. The effect of the multilayer coating on the biocompatibility was identified using immersion and cytotoxicity tests. Better hydroxyapatite formation was observed on the surface of multilayer-coated pure titanium compared to non-treated pure titanium after immersion in the simulated body fluid. Improvement of biocompatibility by multiple surface treatments was identified through various cytotoxicity tests using osteoblast cells.
... 22 Moreover, strontium is effective in reducing the incident of fractures in osteoporotic patients, and SrTiO 3 has also been reported to hold excellent stability and biocompatibility. 23 Zhang et al. prepared the hetero-junction SrTiO 3 /TiO 2 nanotube arrays by hydrothermal treatment of TiO 2 nanotube arrays and obtained improved bioactivity for the hydroxylapatite formation. 24 Li et al. further found that SrTiO 3 /TiO 2 nanotube arrays can stimulate the secretion of cell lopodia, leading to enhanced cell proliferation. ...
Anodized TiO2 nanotube arrays have important applications in the area of photocatalysis and biomedicine. In this study, with the aim of improving the photocatalytic and biomedical properties of TiO2 nanotube arrays, we prepared both single and double layer walled TiO2 nanotube arrays and subjected them to hydrothermal treatment in strontium acetate solution. It was found that fluoride doped SrTiO3/TiO2 nanotube arrays could be formed after hydrothermal treatment without the failure of the single and double layer walled structure. In the case of fluoride doped SrTiO3/TiO2 nanotube arrays with a double layer walled structure, doping of fluoride induced a visible light response, formation of SrTiO3 benefited the separation of photogenerated electron–hole pairs, and the double layer walled structure led to an enlarged surface area. Due to the synergetic effect of above three factors, the fluoride doped double layer walled SrTiO3/TiO2 nanotube arrays demonstrated the highest photocatalytic activity under ultraviolet, visible and simulated solar light irradiation. The degradation rates of methylene blue solution are 0.13 h⁻¹, 0.26 h⁻¹ and 0.53 h⁻¹ respectively. Moreover, ability to induce hydroxylapatite formation on the surface was also examined through an immersing test in simulated body fluid. The results indicated that SrTiO3, doped fluoride and a double layer walled structure could stimulate the hydroxylapatite formation by providing a larger number of hydroxyl ions, hydroxyl radicals and reactive initiation sites, thus the fluoride doped double layer walled SrTiO3/TiO2 nanotube arrays also exhibited the best ability to form hydroxylapatite on the surface.
... Later, the modified alkali and heat treatments-NaOH-CaCl 2 -heat-water that forms calcium titanate on the surfaces of the Ti-were developed [18]. Both treatments conferred Ti and conventional Ti alloys such as Ti-6Al-4V, Ti-6Al-2Nb-1Ta, Ti-15Mo-5Zr-3Al high capacities for bone bonding as well as apatite formation [19][20][21], and the latter modified treatment was effective even for new types of Ti alloys such as Ti-15Zr-4Nb-4Ta, Ti-29Nb-13Ta-4.6Zr, and Ti-36Nb-2Ta-3Zr-0.3O free from elements suspected of cytotoxicity [22][23][24][25]. ...
Titanium metal (Ti) and its alloys are widely used in orthopedic and dental fields. We have previously shown that acid and heat treatment was effective to introduce bone bonding, osteoconduction and osteoinduction on pure Ti. In the present study, acid and heat treatment with or without initial NaOH treatment was performed on typical Ti-based alloys used in orthopedic and dental fields. Dynamic movements of alloying elements were developed, which depended on the kind of treatment and type of alloy. It was found that the simple acid and heat treatment enriched/remained the alloying elements on Ti-6Al-4V, Ti-15Mo-5Zr-3Al and Ti-15Zr-4Nb-4Ta, resulting in neutral surface charges. Thus, the treated alloys did not form apatite in a simulated body fluid (SBF) within 3 days. In contrast, when the alloys were subjected to a NaOH treatment prior to an acid and heat treatment, alloying elements were selectively removed from the alloy surfaces. As a result, the treated alloys became positively charged, and formed apatite in SBF within 3 days. Thus, the treated alloys would be useful in orthopedic and dental fields since they form apatite even in a living body and bond to bone.
... There have been many methods to prepare HA coating on titanium with HA particles, such as plasma spray method [14], spin and dip coating methods [15], deposition techniques [16][17][18][19][20][21][22], thermal spray techniques [2,23], anodic spark discharge [24], chemical treatment [25], electrochemical coating [26], sol-gel coating [27] and laser coating techniques [3,4]. In addition, recent studies found significant advantages of nanosized HA (nanoHA) over large scale counterparts [28][29][30][31][32][33]. ...
In this paper, we presented a comprehensive and complete study of the biological behavior of the bone forming cells, osteoblasts, on the graded nano-biphasic calcium-phosphate/Ti coatings of different compositions by investigating bone cell proliferation, bone cell viability, markers for bone cell differentiation and key genes that encode for known proteins which are important for de novo extracellular matrix and osteoid production. We prepared the gradient nano hydroxyapatite and titanium nanoparticles (nanoTi) composite coating on Ti-6Al-4V implants. Due to the size effects of nano-Ti, this process could be used to sinter nano HA/nanoTi composite coating at low temperature. The gradient coating with different concentration of HA could be prepared by controlling the composition of the nanoparticles, and the composition of nanoHA and beta-tricalcium phosphate in the coating could be varied by controlling the laser power. The coating was characterized with XRD and SEM, and exhibited excellent biocompatibility as well as bioactivity to UMR-106 cells.
... 29,30 Only an integrated bone/implant interface results in long-term stability of the structure and function of the interface. 31,32 For successful osseointegration, the biomaterials should exhibit bioactive interactions with osteoblasts. In general, an apatite layer that forms on the material surface could mimic the environment of the recipient bone to promote adhesion and differentiation of osteogenic cells. ...
Polyetheretherketone (PEEK) exhibits appropriate biomechanical strength as well as good biocompatibility and stable chemical properties but lacks bioactivity and cannot achieve highly efficient osseointegration after implantation. Incorporating bioceramics into the PEEK matrix is a feasible approach for improving its bioactivity. In this study, nanohydroxyapatite (n-HA) and nano-calcium silicate (n-CS) were separately incorporated into PEEK to prepare n-HA/PEEK and n-CS/PEEK biocomposites, respectively, using a compounding and injection-molding technique, and the in vitro degradation characteristics were evaluated. Discs with a diameter of 8 mm were inserted in 8 mm full-thickness cranial defects in rabbits for 4 and 8 weeks, and implantation of pure PEEK was used as the control. Three-dimensional microcomputed tomography, histological analysis, fluorescence microscopy of new bone formation, and scanning electron microscopy were used to evaluate the osseointegration performance at the bone/implant interface. The results of the in vitro degradation study demonstrated that degradation of n-CS on the surface of n-CS/PEEK could release Ca and Si ions and form a porous structure. In vivo tests revealed that both n-CS/PEEK and n-HA/PEEK promoted osseointegration at the bone/implant interface compared to PEEK, and n-CS/PEEK exhibited higher bone contact ratio and more new bone formation compared with those of n-HA/PEEK, implying that n-CS/PEEK possessed a stronger ability to promote osseointegration. These two PEEK biocomposites are promising materials for the preparation of orthopedic or craniofacial implants.
... According to previous studies, when the Ti\ \OH groups on the surface react continuously with SBF, amorphous calcium titanate is formed by bonding with Ca 2+ ; subsequent bonding with PO 4 2− , results in the formation of amorphous calcium phosphate. This amorphous calcium phosphate evolved as follows: DCP (dicalcium phosphate) -OCP (octacalcium phosphate) -TCP (tricalcium phosphate) -HAp (hydroxy apatite) [28][29][30][31][32]. A review of the SEM, EDS, and XRD results of the present study, indicated that the spherical octacalcium phosphate (OCP-Ca 8 (PO 4 ) 6 (OH) 2 ) was formed on the surface after the groups were soaked in SBF. ...
Various surface treatments are used to enhance the biological activity of titanium. Alkali and heat treatments promote the formation of hydroxyl apatite (HAp), which increases the bone-bonding ability in simulated body fluid (SBF). The sodium titanate layer is converted to the more bioactive layer, with sodium-ion removal from alkali- and heat-treated surfaces, via a water treatment. The anatase phase resulting by water treatment is effective in generating apatite nuclei in SBF.In this study, two types of surface treatment were performed to improve the bioactivity of alkali and heat-treated TiO2 nanotubes: One is the only water treatment for 48h. Another is the combination of the acid-solution (10 and 50mM of HCl or HNO3) treatment for 24h and the water treatment for 24h. Each treatment was conducted after the fabrication of alkali-treated TiO2 nanotubes via anodization and an alkali treatment in 5M NaOH. Finally, all of the treated groups were all heated at 550°C. The properties, bioactivity, and cytotoxicity of the alkali-heat treated TiO2 nanotubes were determined after the water or acid treatment. In addition, histological samples were evaluated by inserting implants into bilateral rat tibia for 3 and 6weeks. The concentration of O ions and the amount of anatase phase increased after the HCl treatment. Furthermore, the apatite-forming ability was greatly enhanced with an increase in the amount of anatase phase, especially in the 50mM HCl-treated group. The surface of the water- or 50mM HCl-treated group promoted osteoblastic proliferation and differentiation, thereby allowing effective osteointegration. In the 6-week implant, the uniform new bone layer grew in the case of the HC50 group only. Therefore, we conclude that the HCl treatment constitutes the most favorable surface-modification method for improving the bioactivity of alkali- and heat-treated TiO2 nanotubes.
... Nevertheless, two special absorption peaks at 3571 cm -1 , corresponding to stretch vibration of O-H bond, and 631 cm -1 , corresponding to bending vibration of O-H bond, were observed, which indicated that a number of -OH groups were adsorbed on the surfaces during NaOH pretreatment. Noticeably, the -OH groups was effective for bone-like apatite nucleation in body or simulation body environment [12,13]. Bone-like Apatite Layer. ...
Bone tissue engineering provides a new way to repair the bone defect in orthopaedics. The scaffolds, porous materials with excellent biocompatibility, bioactivity and biodegradability, play an important role in bone tissue engineering. Furthermore, the bioactivity of the pore interior surfaces is very important for cell attachment, differentiation and growth, as well as new bone tissue ingrowth into pores. In this paper, β-TCP was selected as materials of scaffolds, and its bioactivity was improved by activating the interior surfaces of pore walls. The porous β-TCP scaffolds with about 50~300μm of pore size and above 80% of porosity were obtained by 3D-gel-laminated processing. Their surfaces of the scaffolds were easily covered by a low crystallized bone-like apatite layer, which determined by XRD and FTIR, after immersing in 1.5SBF solution following pre-treatment by NaOH solution. MTT and ALP assays were performed after cells cultured on the porous scaffolds with bone-like structure, and the results showed higher proliferation rate and differentiation level than that on the scaffolds without treatment, which indicated that the porous β-TCP scaffolds with bone-like apatite layer on surfaces of pore walls possess higher bioactivity. Therefore, the bioactivity of tissue engineering scaffolds could be improved by deposited bone-like apatite layer on their surfaces.
... [1][2][3][4] This type of chemical and heat treatment has been applied to the porous titanium metal surface layer of an artificial total hip joint, and has been used clinically in Japan since 2007. 5 The above treatment is effective for inducing bone-bonding bioactivity in conventional Ti-based alloys, such as Ti-6Al-4V, 6 Ti-15Mo-5Zr-3Al, 7 and Ti-6Al-2Nb-1Ta. 2 However, these treatments are not effective in inducing apatiteforming ability in the new Ti-Zr-Nb-Ta alloys, 8 which are free from elements suspected of cytotoxicity. Among these alloys, Ti-15Zr-4Nb-4Ta (Ti-15-4-4) alloy shows a high mechanical strength. ...
Ti-15Zr-4Nb-4Ta alloy is an attractive metal for orthopaedic implants, since it is free from cytotoxic elements and shows high mechanical strength. It was recently shown by an animal experiment [1] that this alloy tightly bonds to living bone, when it was subjected to 5 M NaOH solution and 100 mM CaCl 2 solution treatments, heat treatment at 600 or 700 °C, and final water treatment at 80°C. The bonding strength was increased markedly when the heat treatment temperature was increased from 600 to 700°C. This increase of the bonding strength was attributed to the increase in apatite-forming ability of the treated alloy in a simulated body fluid (SBF) [2] with ion concentrations nearly equal to human blood plasma, although its reason was not revealed yet. In the present study, structural changes of the surfaces of the alloy due to the chemical and heat treatments were investigated, and its apatite-forming ability was discussed in terms of the surface structure.
... 2. The samples were immersed for 19 days in a SBF solution with additional PAW1 biovitroceramic (particles under 20 µm) content at 36 ºC in order to form a HA layer formed by a multitude of HA nuclei originating on biovitroceramic precursor. The SBF was prepared by dissolving reagent grade chemicals of NaCl, NaHCO 3 , KCl, K 2 HPO 4 · 3H 2 O, MgCl 2 · 6H 2 O, CaCl 2 and Na 2 SO 4 in distilled water, and buffered at pH 7.40 with tris-hydroxymethyl aminomethane ((CH 2 OH) 3 CNH 3 ) and hydrochloric acid at 36.5 ºC [7]. ...
The aim of this paper is to compare the bioactive behavior generated by two different surface treatments on Ti-6Al-7Nb previous to the implant in the animal knee. One of the treatments consists in soak the sample with NaOH and followed by a subsequent heat treatment. The other treatment consists in immersion for 19 days in a SBF solution with additional PAW1 biovitroceramic (particles under 20 µm) content at 36 ºC. After a long exposure (more than 100 days) of the samples to a simulated body fluid, the surfaces were investigated to clarify what bioactive structure forms on the alloy and how it changes in the body's environment. A knee plate was design for the samples of Ti-6Al-7Nb.
... These treatments will increase also the performance of the implant. The methods for surface modification can roughly be classified as mechanical, chemical and physical according to the formation mechanism of the modified layer on the substrate [1,2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Traditionally hydroxyapatite coatings are used to achieve the promoted bioactivity on a metallic surface [6,19,20]. ...
As-received" and "sand-blasted" commercially pure titanium plates were chemically treated in alkaline and hydogen peroxide solutions in order to improve osseointegration. Both surface modification methods were carried out under optimum conditions stated in the literature. The samples were subjected to a bending cyclic loading under a stress amplitude of 250 MPa and R=0. The fatigue life of the as-received samples decreased from 4.10 5 to 2.10 5 due to surface roughening effect of the surface treatments. On the other hand, sand blasting increased the fatigue life of the sample significantly, although it also increased the surface roughness. The reason is the blasting induced deformation and in turn compressive stresses in the surface vicinity. Chemical treatments applied did not affect the surface roughness of the sand blasted samples. However the fatigue life of the sand blasted samples decreased drastically after chemical treatment. Chemical surface treatments are generally accompanied by a post heat treatment. The decrease in the fatigue life of the sand blasted plates is stemmed from stress relieving effect of the post heat treatment. As a result surface modification methods applied for bioactivity should be also evaluated with respect to its effects on the fatigue performance of the material. The process parameters of the chemical surface treatment should be optimized taking into the account the fatigue life of the implant.
... For an orthopaedic implant to achieve bioactivity, its constituent materials must elicit a specific biological response at the interface of the material, thus facilitating formation of a bond between the tissues and the material 17 . This is often verified by in vivo tests or soaking in simulated body fluids and investigating surface precipitation of hydroxyapatite (HA) 18,19 . Surface treatments are aimed at modifying the interaction with the body to generate a bioactive layer which aids in osseointegration. ...
The clinical outcome of lumbar spinal fusion is correlated with achievement of bony fusion. Improving interbody implant bone on-growth and in-growth may enhance fusion, limiting pseudoarthrosis, stress shielding, subsidence and implant failure. Polyetheretherketone (PEEK) and titanium (Ti) are commonly selected for interbody spacer construction. Although these materials have desirable biocompatibility and mechanical properties, they require further modification to support osseointegration. Reports of extensive research on this topic are available in biomaterial-centric published reports; however, there are few clinical studies concerning surface modification of interbody spinal implants. The current article focuses on surface modifications aimed at fostering osseointegration from a clinician's point of view. Surface modification of Ti by creating rougher surfaces, modifying its surface topography (macro and nano), physical and chemical treatment and creating a porous material with high interconnectivity can improve its osseointegrative potential and bioactivity. Coating the surface with osteoconductive materials like hydroxyapatite (HA) can improve osseointegration. Because PEEK spacers are relatively inert, creating a composite by adding Ti or osteoconductive materials like HA can improve osseointegration. In addition, PEEK may be coated with Ti, effectively bio-activating the coating.
... Kim et al. first introduced alkali and heat treatments, which have been further widely studied in many papers [8]. The treatments of titanium and titanium alloys using NaOH should be adjusted to obtain a titanium oxide layer of optimal thickness which enables gradual transition from the mechanical and corrosion properties of titanium implant to the properties of top oxide layer. ...
... The range of materials known to be biocompatible, and in some cases bio-active, when in contact with bone tissue is now quite extensive. Certain structural metals, notably titanium alloys and some stainless steels, have good bio-compatibility and several surfaces treatments have been developed to encourage bone in-growth [1][2][3][4][5][6]. Mechanical requirements include sufficient strength to avoid plastic deformation, brittle fracture and fatigue crack propagation, preferably with a stiffness at least approximately matching that of bone, to minimise stress shielding. ...
This work relates to porous material made by bonding together fibres of a magnetic material. When subjected to a magnetic field, the array deforms, with individual fibres becoming magnetised along their length and then tending to line up locally with the direction of the field. An investigation is presented into the concept that this deformation could induce beneficial strains in bone tissue network in the early stages of growth as it grows into the porous fibre array. An analytical model has been developed, based on the deflection of individual fibre segments (between joints) experiencing bending moments as a result of the induced magnetic dipole. The model has been validated via measurements made on simple fibre assemblies and random fibre arrays. Work has also been done on the deformation characteristics of random fibre arrays with a matrix filling the inter-fibre space. This has the effect of reducing the fibre deflections. The extent of this reduction, and an estimate of the maximum strains induced in the space-filling material, can be obtained using a simple force balance approach. Predictions indicate that in-growing bone tissue, with a stiffness of around 0.01-0.1 GPa, could be strained to beneficial levels (~1 millistrain), using magnetic field strengths in current diagnostic use (~1 Tesla), provided the fibre segment aspect ratio is at least about 10. Such material has a low Young's modulus, but the overall stiffness of a prosthesis could be matched to that of cortical bone by using an integrated design involving a porous magneto-active layer bonded to a dense non-magnetic core.
... The range of materials known to be biocompatible, and in some cases bioactive, when in contact with bone tissue, is now quite extensive. Certain structural metals, notably titanium alloys and some stainless steels, have good biocompatibility, which can be improved by suitable surface coatings (Ducheyne, Van Raemdonek et al. 1986; De Groot, Geesink et al. 1987; Lacefield 1988; Shirkhanzadeh 1991; Nishiguchi, Kato et al. 1999; Kim, Takadama et al. 2000). Mechanical requirements include sufficient strength to avoid plastic deformation, brittle fracture and fatigue crack propagation, preferably with a stiffness at least approximately matching that of bone (to minimise stress shielding). ...
1. Background Replacement of hip, knee and other joints, usually as a treatment for degenerative arthritis, is becoming increasingly common, with the worldwide market currently worth about $5 billion and an estimated annual growth rate of around 9%. These operations bring pain relief to millions, but the treatment is plagued by a substantial problem. The stem of the prosthesis, which is commonly pushed down into a recess in the host bone, often becomes loose after a time. The problem is getting worse as joint replacement rates rise and operations are carried out on younger and more active patients. Prosthetic implants are attached to bone either with cement or via bone in-growth into a rough or porous surface. Although bone cement provides immediate fixation, cemented implants frequently loosen in time due to the poor wear and fatigue properties of such cement. Furthermore, in-vivo polymerization is likely to take place, with deleterious effects on the surrounding tissue. Strong bone-implant bonding can be achieved in the absence of cement by bone tissue growth into an implant surface which is rough or porous, preferably with channels of around 100-300 µm in diameter (Bobyn, Pilliar et al. 1980). However, this does not occur very readily or quickly and might typically take at least a couple of weeks - a period during which there is a serious danger of complete debonding if exercise is undertaken prematurely. It is now well established (Frost 1987; Akhouayri, Lafage-Proust et al. 2000; Mosley 2000) that bone growth is stimulated by mechanical stress and becomes sluggish in its absence. Resultant phenomena include loss of bone density and strength in astronauts after extended periods in a hypo- gravity environment and localised bone resorption adjacent to prosthetic implants, as a consequence of stress shielding. This latter effect arises because prostheses are stiffer than surrounding bone, inhibiting it from being strained. (Most metals have a stiffness of about 100-200 GPa, whereas that of cortical bone is about 7-27 GPa).
Despite having excellent osteoconductivity and biocompatibility, hydroxyapatite (HA) exhibits
inadequate mechanical properties and bacterial susceptibility, which limits its medical applications.
The present study aims to fabricate 3-aminopropyltrimethoxysilane (3-APTMS) functionalized gold
(Au)-silver (Ag) nanoparticles incorporated in hydroxyapatite bioceramics to overcome this limitation.
Thermogravimetric analysis (TGA), X-Ray difraction, and scanning electron microscopy were carried
out to understand the physical and chemical characteristics of the material. The maximum values of
fracture toughness, hardness, compressive and fexural strength were measured for HA-10 Au/Ag NPs.
Both quantitative and qualitative analyses of antibacterial behavior revealed that the adhesion of
gram-positive (Staphylococcu aureus) and gram-negative (Eschericia coli) bacterial cells were reduced
signifcantly after the incorporation of Au/Ag NPs as compared with the HA control. In addition, the
efect of Au/Ag NPs incorporation on the cellular response was observed for the MG63 cell line. Both
the quantitative and qualitative results indicate signifcantly enhanced cell proliferation with the
incorporation of Au/Ag NPs as compared to HA. The addition of Au/Ag NPs in HA provides a material with
appropriate mechanical, antibacterial, and cellular responses for further consideration.
Plasma electrolytic oxidation coupled with hydrothermal treatment is a relatively new technique to form a hydroxyapatite/TiO2 layer on titanium alloys for biomedical applications. Hence the process allows achieving a bioactive and bactericidal surface by using electrolytes that contain ions (such as calcium-phosphorus and boron) necessary for desired properties. The coating properties are controllable by adjusting the parameters in the PEO process. In the present study, an electrolyte that contains both calcium, phosphorus, and boron ions was used to form a rough and porous oxide layer on Ti6Al7Nb which is known to be less toxic than the most widely used Ti alloy for biomedical applications, Ti6Al4V. A hydroxyapatite and boron-containing oxide layer was obtained after plasma electrolytic oxidation and hydrothermal treatment. Coatings were examined by XRD, XPS, SEM, contact angle measurement system, micro-hardness tester, wear tester, and corrosion measurement system. The results showed that the wear and the corrosion properties of all coated samples increased. Especially boron doping enhanced both the wear and corrosion resistance. Relatively the best corrosion resistance was achieved from CaP-B and the best wear resistance was from HA-B samples. The hardness values and mean surface roughness of all coated samples also increased while the average friction coefficients decreased. The hardness increased from 323 ± 5 HV0.1 to 1084 ± 16 HV0.1 where the coefficient of friction decreased from 0.5672 ± 0.01 to 0.4697 ± 0.03.
Electrical discharge coating (EDC) has been applied to prepare a Ca and P-containing layer on Ti as implant applications. This study aimed to enhance Ca and P incorporation in the coating by absorbing HA on gas using gas-assisted perforated electrodes. The effects of gas flow rate and electrode rotational speed on the coating composition and coating thickness were investigated. Using the gas-assisted perforated electrodes at an appropriate gas flow rate (0.02 L/min) enhanced the Ca and P amount in the coating. In addition, an increase in the rotational speed of the electrode decreased the Ca and P amount in the coating. The coating thickness decreased with increasing electrode rotational speed. The EDC-treated Ti exhibits higher surface hardness and corrosion resistance than Ti. After hydrothermal treatment, the needle and prism HA crystals precipitated on the coating surface, exhibiting hydrophilic property. Furthermore, the hydrothermal treatment slightly improves the corrosion resistance of the EDC-treated Ti.
Corrosion resistance of a titanium (Ti) orthopaedic implant should be as important as its bioactivity and mechanical compatibility capable of determining the future implantation failure rate. Here we presented an in vitro evaluation, using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) in combination with chemical analysis of Ti ion release, on the corrosion resistance of bioactive macroporous (pTi) scaffolds with a surface three-layer film consisting of a top layer of hydroxyapatite (HA) coating, a mid-layer of titanate-based TiO2 gel and an inner layer of anodic TiO2 film. The surface three-layer film was made by using a combination of surface treatment processes including alkali-heat (AH), anodic oxidization (AO), electrochemical deposition (ED) and hydrothermal treatment (HT). Our results showed that compared with the pTi discs without any treatments, the AH slightly improved the corrosion resistance, whereas ED significantly caused corrosion acceleration. We also found that the use of HT after ED made it possible to recover the lost corrosion resistance to approach the highest level of corrosion protection being obtained by AO. The findings in the present study would have immediate reference for designing and preparing of bioactive Ti implants with high corrosion resistance.
Professor Larry Hench first reported that certain glasses are able to spontaneously bond to living bone in 1970. This discovery stimulated research into new kinds of bone‐bonding materials. However, there were no guiding principles for this purpose, and many animals were sacrificed in the effort to establish them. The present authors proposed in 1991 that the bone‐bonding capacity of a material could be evaluated by examining apatite formation on its surface in an acellular simulated body fluid (SBF), without the need of performing any animal experiments. Various kinds of novel bone‐bonding bioactive materials based on Ti metal and its alloys with a number of different functions have been developed using SBF. Some of these have entered clinical use as important bone‐repairing materials. Without the method of SBF evaluation, these novel materials would not have been developed.
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In order to improve the surface biocompatibility of titanium, many techniques have been used for surface biological modification of titanium. In this paper, the surface modification based on solution, including acid etching (AC), alkaline and heat treatment (AH) and micro-arc oxidation (MAO), were used to modify the surface of titanium. The surface physical properties and chemical property and the relatively biocompatibility were investigated in order to find out the difference between different methods. The results showed that the AC treated surface exhibited micro-porous structure with the highest roughness and a pore size of less than 2 μm, AH-treatment provided with a smooth and nano-scale porous structure, and MAO produced a surface with interconnected macro-porous structure with spherical pores. Meanwhile, different methods also change the surface chemical composition, in which titanium and titanium oxide were mainly formed in the surface, sodium titanate gel and rutile were formed on the AH-treated surface and anatase and rutile were formed on the MAO-treated surface. In vitro test results have shown that the MAO treated sample exhibited more conductive to the formation of hydroxyapatite and the growth of bone cell due to rough and macro-porous rutile and anatase while AC treatment had limit influence on the surface activity. It was suggested that MAO processing could be more promising for surface modification of titanium.
The present study addresses two approaches in surface modification targeted at the enhancement of titanium implants’ biocompatibility. The first one comprises alkali heat treatment leading to formation of amorphous sodium titanate layer that encourages bone growth. Alkali heat treatment conducted on Ti Grade 2 and Ti-22Nb-6Zr (at.%) in 5M NaOH solution at 60 °C for 24 hours and different heat treatments at 600 °C. The obtained surface layer on Ti Grade 2 is without cracks, but sample without heat treatment does not contain oxygen that promotes formation of sodium titanate. Layer on Ti-22Nb-6Zr is cracked after all heat treatments, but after 600 °C, 0.5 h there is more modified layer in terms of area and more sodium on the surface than after 600 °C for 1 h. The second approach comprises using porous metallic materials mimicking bone structure and properties. Due to the soft cellular structure of Ti foams, the surface porosity is often compromised by traditional machining methods which lead to surface smearing. The key idea to maintain the porous surface structure after the machining is to use an infiltrant material (wax) filling the foam before the machining and is chemically removed afterwards. The corresponding technological scheme has been developed and described.
Statement of significance:
On the basis of systematic study of apatite formation on a material in a simulated body fluid, various kinds of novel bioactive materials possessing not only bone-bonding activity and but also various other functions such as bone growth promotion, antibacterial activity and osteoinduction have been developed. Some of them are already successfully applied to clinical applications or trials for artificial hip joints and spinal fusion devices. It is shown in the present paper how these novel bioactive materials have been developed.
SrTiO3 nanotube films with good adhesion strengths to Ti substrates were fabricated by using a hybrid approach with a modified anodization and a hydrothermal treatment (HT). The effect of Sr2+ concentration in HT solutions on the morphologies and phase components of the nanotubes were investigated, the SrTiO3 nanotubes formation mechanism was explored, and the adhesion strengths, hydrophilicity and apatite-forming ability of the SrTiO3 nanotubes were also evaluated. The results demonstrated that with increasing the incorporation of Sr2+ into the nanotubes, no obvious changes of the lengths and outer diameters of the nanotubes were observed, but the wall thickness and the crystallinity of SrTiO3 in the nanotubes increased. The accumulation of Sr at the inner tube wall indicated that the reaction of Sr2+ with TiO2 mainly occurred in the vicinity of internal surfaces of the closely arranged nanotubes. The formation of the SrTiO3 nanotubes could be attributed to an in situ dissolution-recystallization process. The SrTiO3 nanotubes exhibited good hydrophilicity and bioactivity, and the induced apatite preferred to nucleating on the nanotubes with higher crystallinity and Sr content, indicating a good bio-adaptability of the SrTiO3 nanotubes for orthopedic application.
This study proposed an electrochemical etching method to modify and control the surface roughness of G2 titanium, and the roughness effects on electrochemical behaviors were further verified by electrochemical impedance spectroscopy (EIS). Through electrochemical etching process within an electrolyte of 3.5 wt.% NaCl, the rough surface, big pits and cavities on titanium surface are suitable for the growth and fixity of bone cells and tissues. When the etched G2 titanium immersed in Hank's solution, bone-like compositions, including calcium and phosphorus of hydroxyl apatite, likely precipitate on such rough surface. For EIS study, the equivalent circuit for molding the rough G2 titanium immersed in the Hank's solution can be express as: (R0) + (C1//R1) + {C2//[R2 + (C3//R3)]}. The internal resistances of electrodes or load wire were simulated by a resistance, the characterizations of electron and charge transportation or diffusion between interfaces was simulated by a RC parallel circuit. It was found that the resistances of G2 titanium, transport wire and counter material appeared as ohmic impedance (R0). The other resistances of oxide film resistance (R1), hydroxyl apatite/electrolyte (R2), and hydroxyl apatite (R3) as the internal resistances. The interface capacitances include contact capacitance (C1), chemical capacitance (C2), and double-layer capacitance (C3).
Microarc oxidation was performed on Ti-6Al-4V in an electrolyte containing calcium and phosphate ions. Samples were hydrothermally treated in different solutions containing calcium and phosphate ions. Various hydroxyapatite coatings were formed. It was found that hydroxyapatite coating is improved by the addition of calcium and phosphate ions in hydrothermal solutions. The addition of phosphate ions promotes the nucleation and growth of hydroxyapatite. But the effect of single calcium ions is not obvious. The addition of calcium and phosphate ions increases the nucleation and growth of hydroxyapatite, but decreases the preferred growth trend in some extent.
The effect of different concentration NaOH aqueous solution on induced deposition of apatite layer on NiTi shape memory alloy in SBF was mesured. The morphology, phases, groups and valency change of element on the surface of chemically treated NiTi before and after soaking in SBF were analyzed by XRD, ESEM and X-ray photoelectron spectroscopy. The results show that the surface of NiTi treated by 1 mol/L NaOH aqueous solution exhibit a higher bioactivity because of formation of sodium titanate. The treated sample can form CO32- containing apatite layer after soaking in SBF for 3 d and reveal relatively little amount of Ni3+ ions releaseing in Hank's solution. With increasing NaOH concentration, not only sodium titanate but also sodium nickate forms on the surface of treated NiTi alloy, which increases incubation period of forming apatite nucleation on it. At the same time, Ni3+ ions releasing from NiTi treated with 5 mol/L NaOH in Hank's solution greatly increase.
A simple strategy to modify the porous structure of the oxide coating formed on Mg by plasma electrolytic oxidation (PEO) is addressed. Post-treatment of PEO coated Mg using 3 M NaOH at 60 C for 1 h modifies its porous structure, helps to seal the smaller pores and decrease the size of medium and bigger size pores, increases the surface roughness but provides a better homogeneity of the surface, changes its chemical nature, improves its corrosion resistance in Hank’s balanced salt solution, facilitate apatite growth in simulated body fluid and promotes cell viability and growth in cell culture media.
Recently, it was found that titanium oxide with specific structure of anastase and rutile possesses a high bioactive characteristic; this result implies the possibility of preparation of more active titanium by heat treatment in oxygen atmosphere. In this paper, Ti-6Al-7Nb with heat treatment was compared with Ti-6Al-7Nb without heat treatment in order to compare the surface characteristics and the mechanical properties. Data about mechanical behaviour are presented. The mechanical behaviour was determined using optical metallography, Scanning Electron Microscopy, Tensile strength and ultramicrohardness. It resulted that the tested oxide films presented passivation tendency and a very good stability. The pronounced porous oxide layer obtained by heat treatment may be expected to facilitate the incorporation of mineral ions from biological fluids and to improve the bioactive bonding with the living bone.
This work deals with surface modification of Ti6Al4V alloy. Compared are the morphology, structure, adhesion and bioactivity of Ti6Al4V after chemical treatment in alkali solution, anodic oxidation in mixed solution of NH4F + H3PO4 and thermal treatment. In both cases of chemical and electrochemical treatment an amorphous layer of TiOx is formed. Results showed that the alkali treatment leads to formation of a 1μm thick bioactive layer with net-structure, which offers a good basis for the growth of Ca-P compounds. The in vitro test confirmed a good bioactivity of this layer. The thermal treatment caused dehydration of this layer, what did not affect the good bioactivity as confirmed by the in vitro test. Anodic oxidation forms a nanotubular layer, which is not bioactive, but the thermal treatment activated this layer.
The present authors’ systematic studies on growth of novel ceramic layers on Ti metal and its alloys by chemical and heat treatments for inducing bone-bonding bioactivity and some other biological functions are reviewed. Ti metal formed an apatite on its surface in a simulated body fluid, when heat-treated after exposure to strong acid solutions to form rutile surface layer, or to strong alkali solutions to form sodium titanate surface layer. Both types of Ti metal tightly bonded to the living bone. The alkali and heat treatment was applied to the surface Ti metal of an artificial hip joint and successfully used in the clinic since 2007. The acid and heat treatments was applied to porous Ti metal to induce osteoconductivity as well as osteoinductivity. The resulting product was successfully used in clinical trials for spinal fusion devices. For the Ti-based alloys, the alkali and heat treatment was little modified to form calcium titanate surface layer. Bone-growth promoting Mg, Sr, and Zn ions as well as the antibacterial Ag ion were successfully incorporated into the calcium titanate layer.
The chemical and heat treatments of metallic biomaterials for the purpose of inducing bone-bonding via forming apatite on the material surface in the body are reviewed. It has been reported that Ti metal bonds to living bone through apatite formation on its surface in the body environment upon heat treatment after exposure to strong acid or alkali solutions so as to become positively or negatively charged on its surface. Successful examples of clinical applications of the resultant products are also provided.
Bioactive layers, which induce apatite formation on their surfaces in the living body and bond to living bone through this apatite layer, can be formed on various kinds of metals and polymers by simple chemical and heat treatments. They are easily and uniformly formed even on irregular inner surfaces of porous materials. Their functions can be varied by incorporating different ions into the bioactive layers through the chemical treatments.
Hydroxyapatite (HAp) has many applications in the medical field. The objective of this study is to produce HAp/Ti composite coating with Supersonic Free-Jet PVD (SFJ-PVD). The SFJ-PVD is a technique to deposit nanoparticles with supersonic gas flow and to form a thick coating film. In a gas evaporation chamber, a source material is evaporated to form nanoparticles in an inert gas atmosphere. The nanoparticles are then carried to a substrate in a deposition chamber with an inert gas flow through a transfer pipe. The gas flow is generated by the pressure difference between the chambers and accelerated to the supersonic flow of 4.2 Mach through a specially designed supersonic nozzle. With SFJ-PVD, we obtain a uniform high-density HAp/Ti composite coating. XRD analysis reveals that the composite coating is composed of Ti and HAp. An in vitro study was carried out to investigate the bioactivity of the HAp/Ti composite coating under simulated body fluid.
One of the most significant accomplishments of ceramic science in the 20th century was the development of bioactive ceramics that spontaneously bond to and integrate with living bone. Many of the bioactive ceramics, represented by Bioglass®, HA, β-TCP, glass-ceramic A-W, self-setting calcium phosphate cements and HA coatings on metallic prostheses, have achieved significant success in clinical bone repairs and replacements. In vitro assessments using simulated body fluid, together with other cellular in vitro and in vivo assessments, have put into an extensive possession of knowledge on the surface chemistry of bioactive ceramics. The surface chemistry is the fundamental to the current challenging research, e.g., bioactive surface functionalizations that endeavor to induce bonelike apatite-forming abilities on ceramics and metals with high fracture resistance, sol-gel derivations of bioactive inorganic-organic hybrids with high malleability, acellular biomimetic processes that aim at ceramic-polymer composites with natural bonelike structure and properties, and utilization of bioactive ceramics in bone tissue engineering that may be highly advantageous over prevailing attempts utilizing natural and synthetic polymers. Bioactive ceramics and related technologies are therefore believed to continue to occupy a prime position in biomedical fields in the 21st century.
This study was aimed to investigate in vitro and in vivo behavior of a Ti6Al7Nb biomaterial with a nanostructured HA-type coating and also the design and realization of a new special knee implant together with a selection of a suitable animal model for preclinical experimentation of the implants.
The metallic material used like substrate alloy for layer deposition was a Ti6Al7Nb alloy obtained by double electron beam melting furnace. In order to obtain a nano-crystalline HA-coating first sodium titanate layer was obtained on the surface and then the implant was immersed in Ringer solution with additional PAW1 biovitroceramic (particles under 20 μm). Different deposition times (5, 10 and 19 days) were employed. Microscopy analysis and corrosion tests of the implants relieves that the nanostructured HA layer after 19 days of immersion shows promising results as regarding the implant employ in preclinical experiments.
After a complex design based on knee bone radiography there has been manufactured two different types of devices for the metallic implants: a metallic plate and a pin. Two plates and two pins were implanted in each animal.
For in vivo experiments the chosen animal model was the mini-pig because of its strong chirurgical resistance and perfect anesthesia toleration. For the testing 10 animals were used for implantation and one for the control. When the plate is implanted the bone has to have a good blood supply after the cut in order to avoid bone to die. All experimented implants were maintained in the animal during six months and periodically inspected. No sign of infection or another problem were observed during this period.
Objectives: This study investigated the effect of hydrothermal treatment with calcium chloride (CaCl2)solutions on fibroblast attachment and proliferation to titanium implants in the presence and absence of fetal bovine serum. Methods: Pure titanium (The Nilaco Corporation, Tokyo, Japan) specimens were prepared, polished (1500 grit), cleaned with ethanol, hydrothermally treated with CaCl2 solutions at 200C for 24hs (Ti-CaCl2). Two different concentrations of CaCl2 solutions were tested (10mM/L and 20mM/L). Titanium specimens without CaCl2 treatment were used as a control. Then, specimens were exposed to L-929 fibroblasts to test the cellular attachment and proliferation after 30 min, 1h, 2h, 5h, 1day, 3day and 1 week with and without fetal bovine serum. The percentage of viable attached cells (cells/ml) for each surface treatment was measured using trypan blue assay. Cellular growth on just culture plate material was used as a negative control. The data (n=5) were statistically analyzed by ANOVA/Tukey test (p<0.05). Results: Without fetal bovine serum after 1 week, a statistically significant (P<0.05) higher cell attachment to titanium control (4.1x1040.5x104) than to Ti-CaCl2 10mM/L (0.7x1040.1x104) or Ti-CaCl2 20mM/L (1x1040.1x104) was revealed. With fetal bovine serum after 1 week, there was a significant (P<0.05) lower cell attachment to Ti-CaCl2 20mM/L (76x1047x104) than to titanium control (142x1043x104). Conclusions: The CaCl2 hydrothermally treated titanium showed lower evidence of fibroblasts attachment than pure titanium did, which means decreasing the liability of fibrosis, and hence, stronger bonding of CaCl2 hydrothermally treated titanium implant to bone (better osseointegration).
Superhydrophilic ZrO2 nanotube layer was prepared by anodic oxidation of commercial pure Zr in aqueous solutions containing 1M (NH4)2SO4 and 0.15M NH4F. The effect of annealing and ultraviolet (UV) irradiation treatment on the microstructure, water contact angle and bioactivity of the ZrO2 nanotube layer was investigated. The as-anodized nanotube layer consists of cubic and amorphous ZrO2, no apatite crystals are deposited on its surface even after immersion in simulated body fluids (SBF) for 30days, exhibiting weak apatite-inducing ability. After annealing at 450°C for 3h, the nanotube layer is composed of cubic and monoclinic ZrO2, and its apatite-forming ability is significantly enhanced because of its lattice structure matching that of apatite, apatite can be induced after immersion in SBF for 15days. UV irradiation of the ZrO2 nanotube layers does not alter their surface morphologies and phase components, however, can improve the bioactivity only when the ZrO2 nanotube layer is well crystallized. The enhanced bioactivity by UV irradiation is thought to result from the abundant basic ZrOH groups on the crystallized ZrO2 nanotube layer. Annealing and UV irradiation treatment do not alter the superhydrophilic nature of the ZrO2 nanotubes.
The use of metals for the replacement of structural components of the human body has been with us for some considerable time. The metals originally used were stainless steels which have gradually been replaced by cobalt-chromium alloys. Although titanium has been used since the late forties, it is only relatively recently that it has gained widespread interest. Titanium and its alloys are being used more and more in preference to the cobalt-chromium alloys and has broadened the field of applications. The features which make titanium such an interesting material are its excellent corrosion resistance in the biological environment, combined with an exception degree of biocompatibility which it shares with only a handful of other materials. In this review the background to the clinical use of titanium is discussed with particular attention to the biological aspects of the material. While there are now many clinical uses for titanium and its alloys their main areas of application are in the field of dentistry and orthopaedics and these are described in some detail.
A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti‐6Al‐4V, Ti‐6Al‐2Nb‐Ta, and Ti‐15Mo‐5Zr‐3Al substrates were treated with 10M NaOH aqueous solution and subsequently heat‐treated at 600°C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali‐ and heat‐treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load‐bearing conditons. © 1996 John Wiley & Sons, Inc.
The purpose of this study is to evaluate the bone‐bonding ability of alkali‐ and heat‐treated titanium alloys. Smoothed‐surface rectangular plates of Ti6Al4V, Ti6Al2Nb1Ta, and Ti15Mo5Zr3Al were prepared. The plates were inserted transcortically into the proximal metaphyses of bilateral rabbit tibiae, with alkali‐ and heat‐treated plates inserted on the right side, and untreated plates on the left. The tensile failure loads between the implants and the bones were measured after 8, 16, and 24 weeks by a detaching test. The untreated implants showed almost no bonding even at 16 weeks, and only weak bonding at 24 weeks. In contrast, treated implants showed bonding to bone at all time periods. Histological examination showed that alkali‐ and heat‐treated alloys bonded directly to the bone. Conversely, the untreated implants had an intervening layer of fibrous tissue between the bone and the plate, or only partial direct contact with the bone. This study demonstrates that alkali and heat treatments enhance the bone‐bonding strength of these titanium alloys. Although in this study even tentative conditions of the treatments enhance the bonding strength of the titanium alloys, further work is required to determine the optimum conditions for treatment to give the highest bonding strength. These new bioactive titanium alloys are available for weight‐bearing and bone‐bonding orthopedic devices. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 48: 689–696, 1999
Bioactive metals with high fracture toughnesses were prepared by forming an alkali titante layer on surfaces of titanium metal and its alloys with an alkali and heat treatments. Apatite-coated polymers with lower elastic moduli were prepared by nucleating the apatite on surfaces of polymers with CaO, SiO2based glass particles in a simulated body fluid and then by growing the apatite nuclei on the polymers in another solution highly supersaturated with respect to the apatite in situ. These novel bioactive materials are believed to be useful as bone repairing materials even under load-bearing conditions.
The essential requirement for an artificial material to bond to living bone is the formation of bonelike apatite layer on its surface in the living body. This apatite layer can be reproduced on its surface even in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. In the present study, Ti metal was treated with various NaOH aqueous solutions, and apatite formation on the resultant metals were examined in SBF. A sodium titanate hydrogel layer was formed on the surface of Ti metal, when it was treated with NaOH solutions with concentrations higher than 0.5 M at 60°C for periods longer than 24h. Thus treated metals exchanged Na+ ion in the surface layer for H3O+ ion in SBF to produce a hydrated titania on their surfaces and to increase the degree of supersaturation with respect to the apatite of SBF. The hydrated titania induced the apatite nucleation and the increased supersaturation accelerated the apatite nucleation. Thus formed apatite nuclei spontaneously grow by consuming calcium and phosphate ions from SBF. These results indicate that bioactive metal can be obtained by a simple alkali treatment.
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)
The purpose of this study is to evaluate the bone-bonding ability of alkali- and heat-treated titanium alloys. Smoothed-surface rectangular plates of Ti6Al4V, Ti6Al2Nb1Ta, and Ti15Mo5Zr3Al were prepared. The plates were inserted transcortically into the proximal metaphyses of bilateral rabbit tibiae, with alkali- and heat-treated plates inserted on the right side, and untreated plates on the left. The tensile failure loads between the implants and the bones were measured after 8, 16, and 24 weeks by a detaching test. The untreated implants showed almost no bonding even at 16 weeks, and only weak bonding at 24 weeks. In contrast, treated implants showed bonding to bone at all time periods. Histological examination showed that alkali- and heat-treated alloys bonded directly to the bone. Conversely, the untreated implants had an intervening layer of fibrous tissue between the bone and the plate, or only partial direct contact with the bone. This study demonstrates that alkali and heat treatments enhance the bone-bonding strength of these titanium alloys. Although in this study even tentative conditions of the treatments enhance the bonding strength of the titanium alloys, further work is required to determine the optimum conditions for treatment to give the highest bonding strength. These new bioactive titanium alloys are available for weight-bearing and bone-bonding orthopedic devices. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 48: 689–696, 1999
Generally, artificial materials implanted into bone defects are encapsulated by a fibrous tissue isolating them from the surrounding bone. Only limited kinds of ceramics are known to bond to living bone without forming the fibrous tissue, and already they are being used clinically as important artificial bones. However, they cannot be used under highly loaded conditions, since their fracture toughnesses are not so high as that of human cortical bone. The present study shows that even pure titanium metal and its alloys can bond to living bone, if their surfaces are pre-treated with alkali hydroxide solutions. Thus-treated metals are believed to be useful as artificial bones even under highly loaded conditions because of their high bone-bonding ability as well as high fracture toughness.
A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti-6Al-4V, Ti-6Al-2Nb-Ta, and Ti-15Mo-5Zr-3Al substrates were treated with 10M NaOH aqueous solution and subsequently heat-treated at 600°C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali- and heat-treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load-bearing conditons. © 1996 John Wiley & Sons, Inc.
All laboratory-made plasma-sprayed hydroxylapatite coatings (HACs) were found to undergo, to different degrees, changes in phase composition, crystallinity, morphology and roughness dependent on plasma spraying parameters (PSPs). The PSPs, which were systematically varied, included the plasma atmosphere, the spraying current and the stand-off distance. Through the determinations of the concentration of impurity phase (CIP) and the index of crystallinity (IOC), the extent of phase purity and the degree of crystallinity of HACs were quantitatively assessed, respectively. Coatings consisting of at least 50% (IOC>50%) of the original crystalline structure and almostly 95% (CIPR
a=14.48m) to a smoother (R
a=4.46 m) one, dominantly influenced by the spraying atmosphere. As the terms of CIP and IOC are defined and established, the biological responses related to phase purity and crystallinity of HACs can be further evaluated in vitro and in vivo.
Plasma spraying is a commonly used technique to apply thin calcium phosphate ceramic coatings. Special consideration is given to retaining the original structure of CPC particles. However, changes are possible. Thus this study focused on plasma spraying induced changes in material characteristics of commercial coatings and their influence onin vitro dissolution. All analysed coatings were found to undergo significant plasma spraying induced changes in phase composition, crystal structure, and specific surface area. The phase transformations depended on the starting particle characteristics. Specifically, -TCP transformed to -TCP. HA was dehydroxylated and transformed to oxyhydroxyapatite (OHA), and partly decomposed to -TCP and tetra calcium phosphate. These transformations lead to a considerable increase ofin vitro dissolution rates at physiological pH.
In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium cylinders with a standard size were implanted in dog femora. Coatings were made by plasma spraying powders of hydroxylapatite, beta-whitlockite, and tetracalciumphosphate particles. The plasma spraying process turns beta-whitlockite into alpha-TCP. Bone bonding and bone formation were evaluated by mechanical push-out tests and histological observations. Hydroxylapatite and tetracalciumphosphate coatings show an interface strength after 3 months of implantation of 34.3 +/- 6.5 MPa and 26.8 +/- 3.9 MPa, respectively, while alpha-TCP and blanco titanium lead to an interface strength of 10.0 +/- 3.5 MPa and 9.7 +/- 1.3 MPa, respectively. Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.
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.
A mechanical and histological evaluation of uncoated and hydroxylapatite-coated titanium implant materials was performed in this study. Mechanical push-out testing results indicated that the hydroxylapatite-coated implants exhibited significantly greater values of maximum interface shear strength and interface shear stiffness than the uncoated implants. Hydroxylapatite-coated implants demonstrated mineralization of bone directly onto the hydroxylapatite surface. The uncoated CP titanium implants showed a predominantly fibrous tissue interface, with only isolated instances of direct implant-bone apposition. An appropriate surface macrotexture, such as the one investigated, may be required to prevent the hydroxylapatite coating from being pulled off of the substrate by applied loads. The use of hydroxylapatite coatings can significantly enhance implant fixation by direct bone ingrowth or apposition by providing a mechanism for establishing considerable attachment strength shortly after implantation.
The purpose of this study was to evaluate the interface attachment strength and histology of hydroxylapatite (HA) coated and uncoated titanium and cobalt-chromium alloy implants. The canine transcortical plug model was utilized. Four different hydroxylapatite coatings were evaluated. In vitro analysis confirmed that all coatings met FDA guidelines for HA coatings. An unspecified FDA parameter, porosity was found to range from 5-15%. Mechanical testing of the bone-implant interface demonstrated large variation in the performance of the coatings. However, further evaluation of two of the coatings did not demonstrate variations in mechanical characteristics. The histologic findings confirmed the mechanical testing results. The coatings which demonstrated the best mechanical characteristics had excellent bone apposition and uniformity and maintenance of the HA coating at all time periods upon histologic evaluation. Conversely, the coatings which demonstrated inferior mechanical characteristics demonstrated variable amounts of bone apposition and moderate to severe coating degradation and breakup. Cell-mediated osteolysis was observed in regions of severe coating degradation, and particle migration was noted in regions far from the interface. It was hoped that the four coatings would behave similarly as they all met current FDA guidelines. The only parameter which differed significantly among the coatings was coating porosity. Our results indicate that coatings with large porosities were associated with increased coating degradation and poor mechanical performance and osteolysis at the bone-coating interface.
Pure soluble silica prepared by a sol-gel method induced bone-like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel-derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bone-bonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel-derived silica and titania are important for hydroxyapatite induction. material which possesses and/or develops both a negatively charged surface and abundant OH groups in a physiologically-related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone-bonding biomaterials.
Our previous study showed that titanium metal forms a bonelike apatite layer on its surface in simulated body fluid when it was subjected to NaOH and heat treatments to form a sodium titanate hydrogel or amorphous sodium titanate surface layer. In the present study, bonding strength of the apatite layer formed on the titanium metals to the substrates were examined under tensile stress, in comparison with those of the apatite layers formed on Bioglass 45S5-type glass, dense sintered hydroxyapatite, and glass-ceramic A-W, which are already clinically used. The NaOH-treated titanium metals showed higher bonding strength of the apatite layer to the substrates, which was maximized by heat treatments at 500 and 600 degrees C, than all the examined bioactive ceramics. It is believed that bioactive metals thus obtained are useful as bone substitutes, even under load-bearing conditions.
A study was undertaken in rabbit tibiae to determine the effects of chemical treatments and/or surface-induced bonelike apatite on the bone-bonding ability of titanium (Ti) implants. Smooth-surfaced plates (10 x 10 x 2 mm) of pure Ti, alkalil- and heat-treated Ti, and bonelike apatite-formed Ti after the treatments were implanted into the tibial metaphyses of mature rabbits. The tibiae containing the implants were harvested at 4, 8, and 16 weeks after implantation and subjected to a tensile testing and histologic evaluation. Biomechanical results showed that both treated implants exhibited significantly higher failure loads compared with untreated Ti implants at all time periods. Histologic examination by Giemsa surface staining, contact microradiography (CMR), and scanning electron microscopy (SEM) in backscatter mode revealed that both treated Ti implants directly bonded to bone tissue during the early postimplantation period, whereas untreated Ti implants formed direct contact with the bone only at 16 weeks. SEM-electron-probe microanalysis (EPMA) examination showed a Ca-P-rich layer at the interface between the treated implants and bone, although the Ca-P-rich layer was not detected on the surface of untreated implants during observation periods. The results of this study suggest that chemical treatments may accelerate the bone-bonding behavior of titanium implants and enhance the strength of bone-implant bonding by inducing a bioactive surface layer on Ti implants.
Apatite--wollastonite-containing glass--ceramic (A--W . GC) has a strong ability to bond to bone and relatively high mechanical strength. Therefore, as a bulk material it has recently been applied clinically even in load-bearing sites. In this study, we modified A--W . GC by altering its composition ratio with the removal of CaF 2 and the addition of B 2O 3, and examined the potential use of the resulting new glass--ceramic as a material for coating on a titanium (Ti) alloy. The bioactivity of this new coating (NC) material and its bonding ability to bone were investigated mechanically and histologically. After implantation of the Ti alloy plate coated with this material into the tibiae of rabbits for 2, 3, 4, 8, and 25 weeks, a detaching test was performed. The detaching failure load of the NC plates was compared with those of A--W . GC plates, hydroxyapatite (HA) plates, and uncoated Ti alloy plates implanted in the same way. The failure load of NC was as high as that of A--W . GC for all periods, whereas it was significantly higher at 3 and 4 weeks than that of HA. Uncoated Ti alloy showed lower failure loads for all periods, differing significantly from the other materials. There was no breakage or detachment of the coating layer observed after the detaching test. Histological examinations by CMR, Giemsa surface staining, and SEM-EPMA showed that NC bonded directly to bone without any intervening soft tissue layer. A calcium--phosphorus-rich layer (apatite layer) was observed within the coating layer, as is the case in A--W . GC. These results indicate that this new glass--ceramic has earlier bone-bonding ability and high mechanical strength, making it a promising coating material.
An NaOH treatment of pure titanium (Ti) forms a sodium titanate hydrogel surface layer with a smooth graded interface structure to the Ti metal substrate. Subsequent heat treatment at 600 degrees C of the NaOH-treated Ti forms an amorphous sodium titanate surface layer with a smooth graded interface structure similar to the Ti metal substrate. These treated Ti metals both form an apatite surface layer with a smooth graded interface structure to the Ti metal substrates in simulated body fluid (SBF). The smooth graded interface structures give a tight bond of the apatite layer to the substrates. Heat treatment at 800 degrees C of the NaOH-treated Ti forms crystalline sodium titanate and a rutile surface layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide. This substrate forms an apatite layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide in SBF. This irregular graded structure gives a less tight bond of the apatite layer to the substrate.
The present authors previously showed that titanium metal forms a bone-like apatite layer on its surface in a simulated body fluid (SBF), when it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mechanically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel layer into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400-500 degrees C, fairly densified at 600 degrees C and converted into crystalline sodium titanate and rutile above 700 degrees C. The induction period for the apatite formation on the NaOH-treated Ti metal in SBF increased with the transformation of the surface gel layer by the heat treatment. Ti metal heat treated at 600 degrees C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.
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