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Significance of Interstitial Bone Ingrowth under Load-bearing Conditions: A Comparison Between Solid and Porous Implant Materials
Abstract
Interstitial bone ingrowth is extremely important for optimum fixation of implanted materials under load-bearing conditions. In this study, three types of biomaterial test piece were manufactured in solid and open-pore structures, and implanted into dog femoral condyles. Bone formation and remodelling were observed histologically and roentgenologically for 24 weeks thereafter. The study demonstrated that, 24 weeks after implantation, thick fibrous tissue surrounded by corticalized bone formed around both solid smooth-surfaced alumina and titanium implants. On the other hand, however, with an implant made of an artificial osteochondral composite material, thickening of ingrown trabeculae could be observed as early as 4 weeks. Bone ingrowth into the titanium fibre mesh was ambundant and increased with time after implantation. This interstitial bone ingrowth resulted in the complete integration of this implant and the viable host bone. Our findings suggest that interstitial bone ingrowth has great significance, even though new bone formation and remodelling follows Wolff's law after the completion of the bonding between the bone and implanted material under load-bearing conditions. The artificial osteochondral composite material could lead to complete integration of the implant and viable bone, suggesting that it is a promising material for joint replacements. Moreover, the tibial joint surface which bore against the polyvinyl alcohol hydrogel surface of this implant remained intact, which suggests that this composite is a very promising biomaterial for use in joint prostheses.
... The infiltration and in situ polymeraisation of polymers into a porous implant, such as plugs, has also been proposed as a soft polymer fixing method ( Figure 5). Using a titanium fibre mesh, Oka et al. partially infiltrated it with a vinyl acid solution, and polymerised, to ensured the PVA hydrogel was fully integrated [164][165][166]. However, histological changes in the opposing articular cartilage were observed, and the attachment between the PVA and the surrounding cartilage remained to be perfected [167]. ...
... The advantage of this implant design was the partial infiltration of the polymer into the implant plug, leaving the lower half porous to encourage bone ingrowth within the titanium scaffold. Once grown, this would ensure a secure fit , thus securely attaching the implant to the joint [165,166]. ...
Hyaline cartilage is a strong durable material that lubricates joint movement. Due to its avascular structure, cartilage has a poor self-healing ability, thus, a challenge in joint recovery. When severely damaged, cartilage may need to be replaced. However, currently we are unable to replicate the hyaline cartilage, and as such, alternative materials with considerably different properties are used. This results in undesirable side effects, including inadequate lubrication, wear debris, wear of the opposing articular cartilage, and weakening of the surrounding tissue. With the number of surgeries for cartilage repair increasing, a need for materials that can better mimic cartilage, and support the surrounding material in its typical function, is becoming evident. Here, we present a brief overview of the structure and properties of the hyaline cartilage and the current methods for cartilage repair. We then highlight some of the alternative materials under development as potential methods of repair; this is followed by an overview of the development of tough hydrogels. In particular, double network (DN) hydrogels are a promising replacement material, with continually improving physical properties. These hydrogels are coming closer to replicating the strength and toughness of the hyaline cartilage, while offering excellent lubrication. We conclude by highlighting several different methods of integrating replacement materials with the native joint to ensure stability and optimal behaviour.
... Here, increasing material porosity was the strategy chosen to decrease its rigidity. Another advantage of porous materials is the possibility of cell ingrowth for further stability of the osseointegrated implant [5,6]. A direct relation between pore size and bone formation is assumed, since it provides surface and space for cell adhesion and bone ingrowth [7]. ...
... For this reason material porosity becomes more and more crucial in implant production. Additionally, quicker and more mature bone formation was obtained using a porous (70% porosity with 170 m mean pore size) rather than a solid structure [6]. It is pointed out in vivo that material porosity fraction plays a crucial role in tissue ingrowth, highlighting that a 30% porosity provides an excellent tissue ingrowth proofed by an increased calcium concentration within the pores [4]. ...
Increased durability of permanent TiAl6V4 implants still remains a requirement for the patient's well-being. One way to achieve a better bone-material connection is to enable bone "ingrowth" into the implant. Therefore, a new porous TiAl6V4 material was produced via metal injection moulding (MIM). Specimens with four different porosities were produced using gas-atomised spherical TiAl6V4 with different powder particle diameters, namely, "Small" (<45 μm), "Medium" (45-63 μm), "Mix" (90% 125-180 μm + 10% <45 μm), and "Large" (125-180 μm). Tensile tests, compression tests, and resonant ultrasound spectroscopy (RUS) were used to analyse mechanical properties. These tests revealed an increasing Young's modulus with decreasing porosity; that is, "Large" and "Mix" exhibit mechanical properties closer to bone than to bulk material. By applying X-ray tomography (3D volume) and optical metallographic methods (2D volume and dimensions) the pores were dissected. The pore analysis of the "Mix" and "Large" samples showed pore volumes between 29% and 34%, respectively, with pore diameters ranging up to 175 μm and even above 200 μm for "Large." Material cytotoxicity on bone cell lines (SaOs-2 and MG-63) and primary cells (human bone-derived cells, HBDC) was studied by MTT assays and highlighted an increasing viability with higher porosity.
... All rights reserved. doi:10.1016/j.mechmat.2008.03.009 and its porous microstructure allows bone ingrowth to form a stable interface with the surrounding bone (Long and Rack, 1998;Chang et al., 1996;. However, the desirable low stiffness of porous titanium comes at the cost of strength and ductility. ...
... It is obvious that a high percentage of open porosity is desirable for bone ingrowth into the entire microstructure. It has been shown that under load-free conditions, bone can grow into pores as small as 50 lm-125 lm (Itala et al., 2001) and the optimal pore size range is considered to be 150 lm-500 lm based on porous hydroxyapatite structures (Chang et al., 1996;Blokhuis et al., 2000;Daculsi and Passuti, 1990;Kujala, 2003). Proper design of porous implants must balance the biological need of high open porosity for maximal ingrowth with the mechanical demands of material integrity for long term durable performance. ...
The reduced stiffness, weight and open porosity of microporous titanium makes it an attractive material possibility for engineering applications ranging from medical implants to impact tolerant structures. To facilitate the design and application of this material, it is necessary to develop an understanding of the relationship between the porous microstructure and mechanical responses of the material. A factorial design of experiment methodology (DOE) is therefore used to systematically compare the effects that several microstructural features have on the mechanical responses via 2D and 3D finite element (FE) simulations. The FE models for the DOE study are all based on a titanium matrix of 12% porosity and the application to orthopedic implants. Five microstructural features are varied to create 32 test cases to study the effects of pore shape, size, orientation, and arrangement, and bone infiltration. The quantitative effects of the features are used to screen their relative importance for elastic modulus, yield stress, and stress concentration factor. The results of the DOE studies of both 2D and 3D numerical simulations demonstrate that bone infiltration into the pores is the most dominant factor for elastic modulus and yield stress. A random arrangement of pores has great effect on local stress concentrations where the local stress fields are primarily concentrated in the regions around closely spaced pores. Bone infiltration greatly reduces the stress concentration in such regions indicating an advantage of bone ingrowth beyond improved interface and attachment. Compared to bone infiltration and pore arrangement and orientation, relative pore size and shape have relatively small effect on the mechanical responses.
... Among them, titanium and titanium alloys are widely used as orthopedic implant materials due to their mechanical and biological properties [9][10][11][12][13]. Moreover, a porous titanium structure allows bone ingrowth into the pores to gain stable osseointegration between the implant and surrounding bone [14,15]. Recently, computer-aided and 3D-printed guided surgery has become popular. ...
Jaw defects can have a variety of causes, including tumors, trauma, and osteomyelitis. The reconstruction of jaw defects has been improved with the free flap technique and sophisticated microvascular techniques. A deep circumflex iliac artery (DCIA) flap provides a large amount of bone for the reconstruction of the mandible. However, various complications and side effects, such as abnormal hip contour, hernia, severe bleeding tendency, gait disturbance, and hypoesthesia, can occur. Iliac bone fracture is not a common complication after DCIA flap harvesting, because the anterior superior iliac spine (ASIS) can include the harvested flap. If an iliac avulsion fracture occurs, various treatment options exist. If severe dislocation of the bone fragment exists, open reduction and internal fixation are required. At this time, orthopedic implants composed of various materials can be used. Among these, when using a 3D-fabricated implant using a Ti6Al4V alloy, the accuracy of the size and shape is excellent, and it can have mechanical–biocompatible advantages. In this study, we report cases of iliac bone fracture after reconstruction of the jaw with a DCIA flap and the treatment modality using a 3D-printed, patient-specific titanium implant.
... at the implantation site, and therefore significantly affecting bone defect reconstruction and remodeling [25][26][27]. Bone remodeling and new bone formation are also associated with load-bearing capacity according to Wolff's law [28]. Ti implants with a conventional shape and solid design have a poor bone regeneration effect [29]. ...
Three-dimensional (3D) printed titanium (Ti-6Al-4V alloy) cages are widely used for spinal fusion applications. However, the structural design and shape of the cages are a major determinant of the optimal clinical outcome. In this study, we constructed a newly designed 3D-printed helical-shaped titanium cage (HTC) with a flexible body, and compared its healing and fusion efficacy in cervical vertebral defects after corpectomy in rabbits to that of a 3D-printed traditional titanium cage (TTC). We performed radiological examinations 1 and 16 weeks after TTC and HTC implantation. We assessed bone ingrowth in TTC and HTC using micro-computed tomography (micro-CT) and histological staining of tissue sections at 16 weeks. The radiographic data showed that the HTC-implanted group had better restoration of vertebral height than the TTC group, indicating a lower risk of cage subsidence. The micro-CT and histological observations showed that HTC promoted bone regeneration and osseointegration more effectively than TTC. Histomorphometry further revealed significant new bone formation in the HTC group compared to the TTC group. These findings demonstrate that HTC has better healing and bone fusion effects than TTC in cervi-cal vertebral defects in rabbits, indicating its potential clinical value.
... To this end, a growing body of evidence continues to inform the ideal surface roughness and variable porous structures that promote osteoblastic differentiation and osteointegration with endplate ingrowth. 19,[37][38][39][40] One of the most compelling findings of our radiographic analysis was widespread and robust osteointegration and ingrowth at the titanium-bone interface (both cranial and caudal in 128 of 136 levels). This initial observation prompted us to develop a fusion-grading scheme that captured endplate ingrowth or endplate fusion, 28 as opposed to traditional fusion-grading schemes that rely solely on the presence of a contiguous bony bridge. ...
OBJECTIVE
Intervertebral devices are increasingly utilized for fusion in the lumbar spine, along with a variety of bone graft materials. These various grafting materials often have substantial cost burdens for the surgical procedure, although they are necessary to overcome the limitations in healing capacity for many traditional interbody devices. The use of bioactive interbody fusion devices, which have demonstrable stimulatory capacity for the surrounding osteoblasts and osteoprogenitor cells and allow for osseointegration, may reduce this heavy reliance on osteobiologics for achieving interbody fusion. The objective of this study was to evaluate the rate of successful interbody fusion with a bioactive lateral lumbar interbody titanium implant with limited volume and low-cost graft material.
METHODS
The authors conducted a retrospective study (May 2017 to October 2018) of consecutively performed lateral lumbar interbody fusions with a bioactive 3D-printed porous titanium interbody device. Each interbody device was filled with 2–3 cm ³ /cage of a commercially available ceramic bone extender (β-tricalcium phosphate-hydroxyapatite) and combined with posterior pedicle screw fixation. No other biological agents or grafts were utilized. Demographic, clinical, and radiographic variables were captured. Fusion success was the primary endpoint of the study, with graft subsidence, fixation failure, and patient-reported outcomes (Oswestry Disability Index [ODI] and visual analog scale [VAS]–back and –leg pain scores) collected as secondary endpoints. The authors utilized a CT-based fusion classification system that accounted for both intervertebral through-growth (bone bridging) and ingrowth (integration of bone at the endplate-implant interface).
RESULTS
In total, 136 lumbar levels were treated in 90 patients. The mean age was 69 years, and 63% of the included patients were female. Half (50.0%) had undergone previous spinal surgery, and a third (33.7%) had undergone prior lumbar fusion. A third (33.7%) were treated at multiple levels (mean levels per patient 1.51). One year after surgery, the mean improvements in patient-reported outcomes (vs preoperative scores) were −17.8 for ODI (p < 0.0001), −3.1 for VAS–back pain (p < 0.0001), and −2.9 for VAS–leg pain (p < 0.0001). Bone bridging and/or appositional integrity was achieved in 99.3% of patients, including 97.8% who had complete bone bridging. No fixation loosening or implant failure was observed at any segment. Low-grade graft subsidence (Marchi grade ≤ I) occurred in 3 levels (2.2%), and intraoperative endplate violation occurred twice (1.5%). High-grade subsidence was not found. No implant failure or revision surgery for pseudarthrosis/subsidence was necessary.
CONCLUSIONS
The use of bioactive titanium interbody devices with a large surface footprint appears to result in a very high rate of effective fusion, despite the use of a small volume of low-cost biological material. This potential change in the osteobiologics required to achieve high fusion rates may have a substantially beneficial impact on the economic burden inherent to spinal fusion.
... The metal scaffolds can only provide a stable platform, but it is difficult to attach other osteoinductive materials to their surface [114]. Titanium alloys have become the most commonly used metal materials in orthopedics because of their excellent biocompatibility, high friction coefficient, high porosity and corrosion resistance [115][116][117]. Not only that, the micro/nano-textured layered titanium morphology can also promote the secretion of exosomes, which in turn promotes bone regeneration [82]. ...
Bone injury repair has always been a tricky problem in clinic, the recent emergence of bone tissue engineering provides a new direction for the repair of bone injury. However, some bone tissue processes fail to achieve satisfactory results mainly due to insufficient vascularization or cellular immune rejection. Exosomes with the ability of vesicle-mediated intercellular signal transmission have gained worldwide attention and can achieve cell-free therapy. Exosomes are small vesicles that are secreted by cells, which contain genetic material, lipids, proteins and other substances. It has been found to play the function of material exchange between cells. It is widely used in bone tissue engineering to achieve cell-free therapy because it not only does not produce some immune rejection like cells, but also can play a cell-like function. Exosomes from different sources can bind to scaffolds in various ways and affect osteoblast, angioblast, and macrophage polarization in vivo to promote bone regeneration. This article reviews the recent research progress of exosome-loaded tissue engineering, focusing on the mechanism of exosomes from different sources and the application of exosome-loaded scaffolds in promoting bone regeneration. Finally, the existing deficiencies and challenges, future development directions and prospects are summarized.
... However, it was found that the biocompatibility of the implant is influenced not only by the chemical composition of the implant, but also by the morphology of its surface. The smooth surface of the implant can cause encapsulation and weaken the fixation of the implant, while the porous surface or coating provides partial or complete bone ingrowth, which increases the bond strength of the bone-implant and reduces the risk of capsule formation around the implant [5,6,7,9,30]. The pore size in such coatings has a significant effect on bone ingrowth, and, consequently, on the reliability of implant fixation. ...
In present work we investigated mechanical properties and phase composition of biocompatible coatings for orthopedic implants, consisting of a titanium sublayer with a developed surface morphology, on which glass-carbon coating was deposited, in order to increase its biocompatibility. The titanium sublayer with thickness 250µm was deposited using the MPN-004 microplasma spraying equipment. The deposition was performed on substrates with size 10 × 20 × 2 mm from Grade 5 Titanium alloy (90% titanium, 6% aluminum, 4% vanadium). The deposition of the glass-carbon coating was accomplished by immersing the samples in a 10% solution of glassy carbon in toluene, followed by drying and heat treatment at 920°C in argon. The process was repeated at least 5-7 times or more until a glass-carbon layer with thickness of 19-50 µm was obtained. The mechanical properties of the moderately rough (about 10 µm) and highly rough (more than 100 µm) samples with and without deposited glass-carbon coating were investigated by means of nanoindentation experiments and then compared. An X-ray diffraction analysis of the samples was performed as well. It was found that the deposition of the glass-carbon coating increases not only the biocompatibility of the investigated material, but also leads to improvement of its mechanical properties.
... Eventually, a layer of connective tissue is exposed in the interface, which is responsible for poor osseointegration. This order of events may cause the failure of the implant, and most of the cases may need a second surgery [136,137]. Therefore, there is a need for a coating surface that provides protection from corrosion and enhances the healing process. Lately, the usage of bioactive coating is gaining more attention as it helps an implant to mimic the natural properties of an organ, aims at enhancing the biomechanical anchorage, and induces osseointegration using either organic or inorganic bioactive materials [138][139][140]. ...
Magnesium alloys are considered the most suitable absorbable metals for bone fracture fixation implants. The main challenge in absorbable magnesium alloys is their high corrosion/degradation rate that needs to be controlled. Various coatings have been applied to magnesium alloys to slow down their corrosion rates to match their corrosion rate to the regeneration rate of the bone fracture. In this review, a bioactive coating is proposed to slow down the corrosion rate of magnesium alloys and accelerate the bone fracture healing process. The main aim of the bioactive coatings is to enhance the direct attachment of living tissues and thereby facilitate osteoconduction. Hydroxyapatite, collagen type I, recombinant human bone morphogenetic proteins 2, simvastatin, zoledronate, and strontium are six bioactive agents that show high potential for developing a bioactive coating system for high-performance absorbable magnesium bone implants. In addition to coating, the substrate itself can be made bioactive by alloying magnesium with calcium, zinc, copper, and manganese that were found to promote bone regeneration.
... [26,28] In addition, Ti-scaffolds have desired properties, such as the uniform structure, strength, low stiffness, high porosity, corrosion resistance, and high coefficient friction. [29] We used real-time PCR, immunofluorescence staining, Alizarin Red Staining, and alkaline phosphatase (ALP) activity to confirm the osteogenesis of the hMSCs under the induction of hMSC-derived exosomes. The cell-free 3D Ti-scaffolds were also applied to induce bone tissue regeneration for 4 and 12 weeks in vivo. ...
Implantation of stem cells for tissue regeneration faces significant challenges such as immune rejection and teratoma formation. Cell‐free tissue regeneration thus has a potential to avoid these problems. Stem cell derived exosomes do not cause immune rejection or generate malignant tumors. Here, exosomes that can induce osteogenic differentiation of human mesenchymal stem cells (hMSCs) are identified and used to decorate 3D‐printed titanium alloy scaffolds to achieve cell‐free bone regeneration. Specifically, the exosomes secreted by hMSCs osteogenically pre‐differentiated for different times are used to induce the osteogenesis of hMSCs. It is discovered that pre‐differentiation for 10 and 15 days leads to the production of osteogenic exosomes. The purified exosomes are then loaded into the scaffolds. It is found that the cell‐free exosome‐coated scaffolds regenerate bone tissue as efficiently as hMSC‐seeded exosome‐free scaffolds within 12 weeks. RNA‐sequencing suggests that the osteogenic exosomes induce the osteogenic differentiation by using their cargos, including upregulated osteogenic miRNAs (Hsa‐miR‐146a‐5p, Hsa‐miR‐503‐5p, Hsa‐miR‐483‐3p, and Hsa‐miR‐129‐5p) or downregulated anti‐osteogenic miRNAs (Hsa‐miR‐32‐5p, Hsa‐miR‐133a‐3p, and Hsa‐miR‐204‐5p), to activate the PI3K/Akt and MAPK signaling pathways. Consequently, identification of osteogenic exosomes secreted by pre‐differentiated stem cells and the use of them to replace stem cells represent a novel cell‐free bone regeneration strategy. Exosomes secreted from human mesenchymal stem cells (hMSCs) pre‐differentiated for a certain period of time can serve as inducers to induce osteogenic differentiation of hMSCs in vitro. They can decorate 3D printed titanium alloy scaffolds, which are further implanted into radial bone defect. They are found to enable the scaffolds to achieve efficient cell‐free bone regeneration in vivo.
... Moreover, the aseptic loosening and failure of implants may be attained as a result of bone resorption caused by stress shielding [94,97]. The bulk Ti surface may develop interfacial fibrous tissue to create encapsulation that separates the implants from their surroundings which finally leads to poor bone-implant interfacial bonding [98]. ...
Selective Laser Melting (SLM) is one of the most important additivee manufacturing (AM) techniques used for developing the structures and the properties of different biomaterials such as stainless steel, Co-Cr alloys as well as titanim (Ti) and it alloys. In recent years, manufacturing of SLM-Ti materials for various biomedical applications has received much research attention due to the high engineering value of this advanced process in medicine. By SLM technique, it can be produced highly Ti implants along with unique structures and characteristics; especially, mechanical, tribological and corrosion properties, throughout precise controlling of different effective parameters. This review article aims to provide a comprehensive summary of the expermental data performed recently via the researchers and speciallist for developing the mechanical, wear and corrosion properties of SLM-Ti implants. The integration between the microstructural features of SLM-Ti and these vital characteristics is also analyzed and evaluated with a serious endeavor to increase the knowledge about the influence of SLM process and its technical parameters on the structure and the performance of diverse Ti materials used for medical purposes.
... Another limitation is that the skeletal maturity was not reached with 3 months of age of the rabbits that might have biased the study. Nevertheless, this model is more realistic concerning the clinical application when compared to similar studies aiming the effect of surface modifications on osseointegration: On the one hand, there is the advantage in terms of full weight-bearing compared to implantation in iliac crest (Biemond et al., 2011), calvaria (Wang et al., 2015), or drilled cavities in the cortical bone of the proximal tibia (Braem et al., 2014) which is important especially with regard to early bone ingrowth (Chang et al., 1996;Kienapfel et al., 1999). On the other hand, the exact implant position is favorable compared to significant variation in the position after transverse implantation into the metaphyseal portion of the distal femur (Dean et al., 1995). ...
For cementless total joint replacement implants, the biological response to physicochemical surface characteristics is crucial for their success that depends on fixation by newly formed bone. In this study, the surface of TiAl6V4 (Tilastan®) implants was modified by (a) corundum blasting, (b) corundum blasting followed by electrochemical calcium phosphate (CaP) deposition, and (c) titanium plasma spraying followed by electrochemical CaP deposition. All modifications resulted in a surface roughness suitable to enhance primary implant stabilization and to favor osteoblast adhesion and function; the thin, biomimetic CaP coating is characterized by fast resorbability and served as chemical cue to stimulate osteogenesis. After implantation in a full weight‐bearing rabbit intramedullary distal femur model, osseointegration was investigated after 3, 6, and 12 weeks. For all modifications, new bone formation, occurring from the endosteum of the femoral cortical bone, was observed in direct contact to the implant surface after 3 weeks. At the later time points, maturation of the woven bone into lamellar bone with clearly defined osteons was visible; the remodeling process was accelerated by the CaP coating. The ingrowth of newly formed bone into the pores of the titanium plasma sprayed surfaces indicates a strong interlock and finally implant fixation. Our findings indicate a positive impact of the tested surface modifications on osseointegration.
... Due to its superior mechanical strength, the present layered ceramic composite may offer an alternative to metal-only implants (such as titanium) used currently to replace critical bone defects [28,45,46]. It was shown by our results that the increase in TCP after sintering has a limited effect on the bending strength. ...
... PVF sponge has a PVA cross-linked construction from the effect of formalin. Marked osteogenesis in the scaffold might be induced by stem cells deposited on the porous scaffold by coating with a chemical agent, which was used as an adhesive [26]. ...
A formalin-treated polyvinyl-alcohol (PVF) sponge is convenient as a scaffold because its configuration is easily modified. However, coating the sponge with an adhesive chemical agent is necessary to attach bone marrow cells (BMCs) to the sponge structure. Moreover, it was considered that a hybrid scaffold composed of a sponge and enveloped cylindrical porous hydroxyapatite (HA) would be convenient. In this study, the effect of leucine (Leu) coating on a PVF sponge was examined for osteogenesis on an HA/PVF hybrid scaffold by rat BMCs (rBMCs). In an in vivo assessment, the sponge immersed in Leu solution (10 mg/ml) was inserted into the hollow center of cylindrical HA. The sponge received 1.5 × 106 rBMCs obtained from male Fischer 344 rats. The hybrid scaffolds were then implanted subcutaneously of syngeneic rats for 6 weeks. In vitro assessment of Leu to hard tissue formation with coating on the well or addition in rBMC culture medium was also performed in a 6-well plate for 2 weeks. In vivo examinations showed the excellent effect of Leu coating on PVF sponge. Leu-coated PVF sponge in the scaffolds showed marked new bone formation in the pores by histological examination. Leu-coated PVF sponge showed a high quantity of osteocalcine (OC). HA might prevent the release of rBMCs from PVF as a barrier. In in vitro examinations, the quantity of OC in rBMC culture with and without the addition of Leu in culture medium showed no significant difference. However, addition of Leu showed significant ALP activity level in culture medium. Leu coating in culture plate wells showed no influence on the quantity of OC. It was concluded from the results that Leu might prevent the emigration of rBMCs to the outside of the scaffold and promote the differentiation of cells to osteoblasts in the scaffold.
... PVF sponge consists of PVA cross-linked construction by formalin. Stem cells must attach to the structure of the scaffold to induce osteogenesis by the cells in a porous scaffold [11,12]. However, the sponge is inappropriate for keeping cells because of the fibrous construction. ...
Although hydroxyapatite is commonly used as a scaffold for bone regeneration, sponges may be suit-able because of the adaptability to the defect. To use as a scaffold, the fiber of sponge would be coated with any adhesive to storage stem cells in the sponges. Fiber in the structure of commercially available sponges was coated by immersion in dextran solution and air dried. After seeding of rat bone marrow cells (rBMCs), the sponges were implanted subcutis of rats for esti-mate osteogenesis in vivo. The level of osteocalcin was 25.28 ± 5.71 ng/scaffold and that of Ca was 129.20 ± 19.69 μg/scaffold. These values were significantly high-er than those in sponges without dextran coating (p < 0.01). It was thought that rBMCs could be stored on the shelf by dextran deposition in the fiber of the sponge. In vivo examination, dextran induced osteo-genesis by rBMCs in many spaces in the inner struc-ture of the sponge.
... So they can influence the accuracy of the formulas obtained by fitting the experimental data. Chang et al. [31] pointed out the significance of bone in growth under load-bearing conditions. Thus, the load bearing is one of the important functions for implants. ...
The use of porous structures is gaining popularity in biomedical implant manufacture fields due to its ability to promote increased osseointegration and cell proliferation. Selective laser melting (SLM) is a metal additive manufacturing (MAM) technique capable of producing the porous structure. Adjusting the parameter of scan line spacing is a simple and fast way to gain porous structures in SLM process. By using the medical alloy of Ti6Al4V, we systematically study the influence of the scan line spacing on pore characteristics and mechanical properties of porous implant for the first time. The scanning electron microscope (SEM) results show that the porous Ti6Al4V implants with interconnected pore sizes which ranges from 250 to 450 mu m is appropriate for compact bone. The compression strength and modulus of the porous Ti6Al4V implants decrease with the increase of the scan line spacing, and two equations by fitting the data have been established to predict their compression properties. The compressive deformation of the porous Ti6Al4V implants presented an adiabatic shear band (ASB) fracture, which is similar to dense Ti6Al4V owing to the dense thin wall structures. The ability to create both high porosity and strong mechanical properties implants opens a new avenue for fabricating porous implants which is used for load-bearing bone defect repair and regeneration.
... Mostly, a layer of connective tissue (CT) is found in the interface, which is responsible for poor osseointegration. 5,6 Silica-based bioactive glasses have supplied successful solutions to different bone defects and soft tissue treatments during the last decades. 7 The biocompatibility and the positive biological effects of their reaction products after implantation 8 have made silica-based bioactive glasses one of the most interesting bioceramics. ...
The present article deals with the development of 3D porous scaffolds for bone grafting. They were prepared based on rapid fluid infiltration of Al 2 O 3-SiO 2 sol into a polyethylene non-woven fabric template structure. Titanium dioxide in concentration equal to 5 wt% was added to the Al 2 O 3-SiO 2 mixture to produce Al 2 O 3-SiO 2-TiO 2 composite scaffolds. The prepared scaffolds are characterized by means of X-ray diffraction, scanning electron microscopy and three-point bending test techniques. The bioactivity of the produced bodies is discussed, including the in vitro and in vivo assessments. The produced scaffolds exhibit mean total porosity of 66.0% and three-point bending strength of 7.1 MPa. In vitro studies showed that MG-63 osteoblast-like cells attach and spread on the scaffolds surfaces. Furthermore, cells grew through the scaffolds and start to produce extra-cellular matrix. Additionally, in vivo studies revealed the ability of the porous scaffolds to regenerate bone tissue in femur defects of albino rats 5 months post surgery. Histological analysis showed that the defect is almost entirely filled with new bone. The formed bone is characterized as a mature bone. The produced bone grafts are intended to be used as bone substitute or bone filler as their degradation products caused no inflammatory effects.
... Mostly, a layer of connective tissue (CT) is found at the interface, which is responsible for poor osseointegration. 13,14 Coating of Al 2 O 3 with bioactive materials is an area of ongoing research. Ignatius et al. 12 concluded that the osseointegration of Al 2 O 3 ceramics could be improved by a coating made of a bioactive glass ceramic material. ...
The present work aims at synthesis and study the bioactivity of porous alumina scaffolds coated with calcium pyrophosphate. Characterization of the formed calcium pyrophosphate and the coated scaffolds was assessed by X-ray diffraction analysis and scanning electron microscope examinations. The in vivo studies revealed the ability of the porous scaffolds to regenerate bone tissue in femur defects of albino rats. Histological analysis showed that the defect is almost entirely filled with new bone. The formed bone is characterized as a mature bone. The produced bone grafts are intended to be used as bone substitute or bone filler.
... However, as observed in our present experiments and confirmed by many other studies, surface coating treatments are unreliable because of the absorption and degradation of the surface materials [24][25][26]. Besides, although some studies have reported the osseointegration effects of macroscopic or microscopic holes in coatings, such as HA and titanium, respectively [33][34][35][36], no studies have previously considered combining macroscopic holes and HA coatings to achieve better osseointegration. In our design, a porous surface combining macroscopic holes (2 mm in diameter) and an HA coating was adopted to achieve better stability, and our results indeed indicate a better locking fixation from both histological and biomechanical aspects. ...
This study aimed to observe the osseointegration of hollow porous titanium prostheses (HPTP) loaded with cancellous bone matrix (CBM) in rabbits using histological and biomechanical perspectives. Experimental samples were implanted into the lateral femoral condyles of 66 New Zealand rabbits, allocated into the following groups: non-porous prosthesis group (Group A, n=22); HPTP group (Group B, n=22); HPTP+CBM group (Group C, n=22). The rabbits were sacrificed at 3, 8 and 12 weeks, postoperatively. X-ray analyses, microscopy techniques and morphological measurement software and mechanical tests were used for evaluation. At each time point, the tissues surrounding the implants were similar in all of the groups, with bony in-growth into the 2-mm round holes observed for the defects in Groups B and C. However, the internal bone formation was significantly better in Group C than in Group B at different time points (P<0.01). Biomechanically, the pull-out forces were significantly greater in Groups B and C than in Group A (P<0.01), with no difference between Groups B and C (P>0.05). These results suggest that bone can grow into the cavities of HPTP to achieve more stable locking fixation, and those osteogenic materials, such as CBM, can enhance osteogenesis to achieve better osseointegration between the implant and the host bone.
... Due to its superior mechanical strength, the present layered ceramic composite may offer an alternative to metal-only implants (such as titanium) used currently to replace critical bone defects [28,45,46]. It was shown by our results that the increase in TCP after sintering has a limited effect on the bending strength. ...
This study presents the design, processing, properties and potential applications of a novel layered bio-ceramic composites consisting of three different micro-porous calcium phosphate coatings on strong zirconia cores manufactured using a recently developed slip coating-deposition and coating-substrate co-sintering technique. Detailed microstructures of the three graded micro-porous calcium phosphate coatings, and the coating/substrate interface have been investigated. Also, the flexural strength of the bio-ceramic composite and the bonding state between the coatings and zirconia substrate have been characterized. A preliminary and limited in vitro cell test indicates that the new scaffold composite has no cytotoxicity to the fibroblasts which can attach, proliferate and grow on the coating surfaces. Because of the combination of bio-function and strength, such layered load-bearing bio-ceramic composites are a potential candidate for large-scale head bone repairs.
... Titanium-based foams inherit the excellent mechanical and biological properties of titanium and its alloys and have potential applications for structural materials and porous bone-replacement implants (Chang et al., 1996;Dunand, 2004;Wen et al., 2002a,b). In particular, as a potential implant material, stiffness of the porous material drops with the square of relative density to be comparable to bone stiffness and the open porosity allows bone ingrowth (Gibson and Ashby, 1997;Spoerke et al., in press). ...
The porous microstructures of metallic foams cause microscopic stress and strain localization under deformation which reduces the damage tolerance and therefore limits application of the materials. In this paper, the deformation of a relatively low porosity porous titanium is examined using two-dimensional (2D) plane strain and three-dimensional (3D) finite element models to identify the accuracy and limitations of such simulations. To generate the finite element models, a simulated microstructure was created based on micrographs of an experimental material. Compared to the 2D models, the 3D models require smaller model size to obtain convergent results. The macroscopic responses predicted by the 3D models are in reasonable agreement with experimental results while the 2D models underestimated the response. In addition, 3D models predicted more uniform microscopic field variable distributions. 2D models predicted higher probability of Von Mises stress and equivalent plastic strain exceeding a certain value and therefore overestimate the failure probability of the material.
... It has been repeatedly suggested [11][12][13][14][15][16] that making prostheses of porous metal might help to solve both the poor bonding and the stress shielding problems. Provided the pore size is suitable (~100-300 µm) [17] and the internal surfaces are bio-compatible or bio-active, bone in-growth can readily occur, leading to strong interfacial adhesion. ...
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.
... 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). It has been recognised (Chang, Oka et al. 1996; Oka, Chang et al. 1997; Hutmacher 2000; Kang, Yoon et al. 2002; Livingston, Ducheyne et al. 2002; Vehof, Haus et al. 2002) that potential for both stiffness matching and bone in-growth channels is offered by open-celled, highly porous metals. A possible problem with such highly porous materials is that they are unacceptably weak, particularly under tensile loading (Gibson 2000; Markaki and Clyne 2001). ...
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).
... In particular, we observe that as a potential implant material, it is comparable to bone stiffness in that its stiffness as a porous material drops with the square of relative density, and the open porosity allows complete bone ingrowth [Gibson and Ashby 1997;Spoerke et al. 2005]. These properties make porous titanium a promising material to solve the inherent problems of monolithic metallic implants, such as the "stress shielding" effect [Chang et al. 1996;Li et al. 2004;Spoerke et al. 2005;Wen et al. 2002a;Wen et al. 2002b]. However, the porous microstructure of the foam leads to the concentration of stress and strain near pores under load-bearing conditions, which results in reduced strength and ductility. ...
To facilitate the design and application of porous titanium and titanium foam, numerical simulation of their mechanical behavior is essential. The concept of a representative volume element (RVE) is essential to obtain accurate estimates of the properties. Because of the high contrast between the properties of the two phases (pore vs. matrix), it is impractical to obtain a single RVE independent of boundary conditions to provide accurate predictions. We suggest that a set of small domain RVEs can be used instead, as long as the average of the small domains provides a convergent result. Two mixed boundary conditions simulating uniaxial proportional loading were designed and implemented on several 2D and 3D finite element models at different length scales, that is, containing different numbers of pores. The two boundary conditions provide opposite biased responses. Convergence of both the macroscopic and the microscopic elastoplastic responses associated with the boundary conditions is demonstrated here. By this approach, RVEs that are prohibitively large according to Hill's definition are divided into reasonably small ones associated with special boundary conditions, and the error of predictions associated with model size can be estimated.
... Mostly, a layer of connective tissue (CT) is found in the interface, which is responsible for poor osseointegration. 5,6 Silica-based bioactive glasses have supplied successful solutions to different bone defects and soft tissue treatments during the last decades. 7 The biocompatibility and the positive biological effects of their reaction products after implantation 8 have made silica-based bioactive glasses one of the most interesting bioceramics. ...
The present article deals with the development of 3D porous scaffolds for bone grafting. They were prepared based on rapid fluid infiltration of Al2O3-SiO2 sol into a polyethylene non-woven fabric template structure. Titanium dioxide in concentration equal to 5 wt% was added to the Al2O3-SiO2 mixture to produce Al2O3-SiO2-TiO2 composite scaffolds. The prepared scaffolds are characterized by means of X-ray diffraction, scanning electron microscopy and three-point bending test techniques. The bioactivity of the produced bodies is discussed, including the in vitro and in vivo assessments. The produced scaffolds exhibit mean total porosity of 66.0% and three-point bending strength of 7.1 MPa. In vitro studies showed that MG-63 osteoblast-like cells attach and spread on the scaffolds surfaces. Furthermore, cells grew through the scaffolds and start to produce extra-cellular matrix. Additionally, in vivo studies revealed the ability of the porous scaffolds to regenerate bone tissue in femur defects of albino rats 5 months post surgery. Histological analysis showed that the defect is almost entirely filled with new bone. The formed bone is characterized as a mature bone. The produced bone grafts are intended to be used as bone substitute or bone filler as their degradation products caused no inflammatory effects.
The Ilizarov technique has been continuously innovated to utilize tensile stress (TS) for inducing a bone development‐like regenerative process, aiming to achieve skeletal elongation and reconstruction. However, it remains uncertain whether this distraction osteogenesis (DO) process induced by TS involves the pivotal coupling of angiogenesis and osteogenesis mediated by type H endothelial cells (THECs). In this study, it is demonstrated that the Ilizarov technique induces the formation of a metaphysis‐like architecture composed of THECs, leading to segmental bone regeneration during the DO process. Mechanistically, cell‐matrix interactions‐mediated activation of yes‐associated protein (YAP)/transcriptional co‐activator with PDZ‐binding motif (TAZ) transcriptionally upregulates the expression of Notch1 and Delta‐like ligand 4, which act as direct positive regulators of THECs phenotype, in bone marrow endothelial cells (BMECs) upon TS stimulation. Simultaneously, the Notch intracellular domain enhances YAP/TAZ activity by transcriptionally upregulating YAP expression and stabilizing TAZ protein, thus establishing the YAP/TAZ‐Notch circuit. Additionally, TS‐stimulated BMECs secrete exosomes enriched with vital molecules in this positive feedback pathway, which can be utilized to promote segmental bone defect healing, mimicking the therapeutic effects of Ilizarov technique. The findings advance the understanding of TS‐induced segmental bone regeneration and establish the foundation for innovative biological therapeutic strategies aimed at activating THECs.
Metallic lattice structures have interconnected porosity for promoting osseointegration and stiffness comparable to bone ideal for minimizing stress shielding. These benefits have caused a widespread proliferation of porous metal scaffolds in orthopedic implants. Once implanted, these devices experience complex stress states under physiological loading. To design these structures to mimic the mechanical behavior of bone, their performance under these conditions must be understood. This study explores the effects of stress state on the mechanical behavior of three lattice structures across a range of clinically relevant porosities. The scaffolds were fabricated via 3D printing Ti6Al4V using LBPF. The gyroid exhibited more efficient mechanical performance at equivalent porosity than the other structures for all loading modes. Stress state has a statistically significant impact on the strength of the scaffolds. This study provides the first dataset on the impact of stress state on the fracture of 3D printed biomimetic scaffolds for orthopedic applications.
The results obtained from this work reveal that high porous titanium foams have fracture mechanical properties that meet and exceed the required properties of both cortical and cancellous bones. With their good biocompatibility, light weight, strong structural integrity and possibility of bone in-growth these foams are suitable for biomedical applications.
Purpose Evaluation of clinical tolerance and scanning electron microscopy study of the bio-colonisation of a porous ceramical alumina implant after evisceration of the rabbit. Preliminary results. Methods Sixteen white New Zealand rabbits were eviscerated. A porous hydroxyde alumina ball was implanted in the opened sclera and explanted 15, 30, and 90 days after implantation. Clinical tolerance was assessed and implant tissular ingrowth was analyzed by scanning electron microscopy. Results One infection was observed and there was no conjunctival breakdown. Fibrovascular ingrowth occurred as soon as 15 days after implantation, and was full at one month. Conclusion Porous alumina implant orbital tissue tolerance and fast fibrovascular ingrowth in the rabbit socket suggest promising result in the human anophthalmic socket.
This chapter provides an overview of orthopedic research using animal models, with emphasis on approaches that have dominated the field for the past 5–10 years. Some of the most successful orthopedic procedures, such as joint replacement, tendon healing, fracture treatment, use of biomaterials, and osteoporosis, to name a few, have relied heavily on animal experiments. There are, however, many orthopedic problems in humans that have not been solved because only relatively advanced stages of the disease can be studied and no proper control group is available. Furthermore, the basic mechanisms of some diseases are still unknown because of lack of animal models. Tissue engineering and gene therapy in orthopedics are rapidly emerging as individual disciplines, and the use of animal models will be essential before human clinical trials can be initiated. Orthopedic surgeons interested in pursuing an idea or hypothesis must first consider the appropriate animal model and understand interspecies differences. This means acquiring sound knowledge not only of the anatomy, biology (including response to different anesthetics and analgesics), biomechanics, and physiology of the various animals, but their general husbandry requirements, including appropriate nutrition and housing, as well.
This chapter discusses the important points related to successful implantology. Some of these points include: bone healing, hemocompatibility, cell adhesion, adsorption, spreading, proliferation, and cell growth. The dental implants, usually made from titanium materials, are biocompatible metal anchors surgically positioned in the jawbone underneath the gums to support an artificial crown where the natural teeth are missing. There are three main types of dental implants: the root form implants, the plate form implants, and the subperiosteal implants. The four major factors influencing the success rates of placed implants include: correct indication and favorable anatomic conditions (bone and mucosa), good operative technique, patient cooperation (oral hygiene), and adequate superstructure. For both dental and orthopedic implant surgeries, bone healing is the major step immediately after implant placements. There are principle steps of peri-implant bone healing. The first healing phase, osteoconduction, relies on the recruitment and migration of the osteogenic cells to the implant surface, through the residue of the peri-implant blood clot.
Over the last few decades bioceramics have improved the quality of life of millions of people. The term '. bioceramic' encompasses a wide range of materials used in skeletal repair and sometimes in soft tissue repair. Applications of bioceramics are varied, ranging from repair or replacement of damaged bones or joints to artificial heart valves and even keratoprostheses. Equally the types of ceramics used are diverse (ranging from fully dense high strength aluminium oxide to low density porous calcium phosphates), as are the reactions these ceramics trigger at the implantation site.In this chapter we will introduce the most important ceramic materials used in the human body and present their main applications. The main part of the chapter will concentrate on the possible reactions of the surrounding organic tissue to the implant material, which depends primarily on the material used (including its chemical composition, porosity and surface roughness) but also on the type of tissue, the age and health status of the patient, any accompanying medical treatment, mechanical loading and many other factors.
The second edition of Bioscience and Bioengineering of Titanium Materials is an essential resource for anyone researching titanium in its fundamental aspects and in medical/dental applications. The book organizes and processes the findings from over 2,000 published articles and studies into a coherent and easily accessible volume, deftly weaving together older and newer technologies to give a clear overview. Bridging the gap between medical/dental and engineering/technology areas, the book covers material classification, fabrication and modification, as well as applications and biological reactions to titanium implants. The author, with extensive work in academics and industry, helps medical practitioners and students answer many practical questions, including: What is titanium? What type of titanium materials should I use in this case? How can I fabricate my design using titanium? Are there any alternative materials or methods? In the second edition, macro-, micro-, and nano-texturing of titanium surfaces, tissue engineering-related materials including scaffolds, and functionally graded materials and structures are extensively included and analyzed.
In recent years a paradigm shift in understanding of human bone formation has occurred that starts to change current concepts in tissue engineering of bone and cartilage. New discoveries revealed that fundamental steps in biomineralization are enzyme driven, not only during hydroxyapatite deposition, but also during initial bioseed formation, involving the transient deposition and subsequent transformation of calcium carbonate to calcium phosphate mineral. The principal enzymes mediating these reactions, carbonic anhydrase and alkaline phosphatase, open novel targets for pharmacological intervention of bone diseases like osteoporosis, by applying compounds acting as potential activators of these enzymes. It is expected that these new findings will give an innovation boost for the development of scaffolds for bone repair and reconstruction, which began with the use of bioinert materials, followed by bioactive materials and now leading to functional regenerative tissue units. These new developments have become possible with the discovery of the morphogenic activity of bioinorganic polymers, biocalcit, bio-polyphosphate and biosilica that are formed by a biogenic, enzymatic mechanism, a driving force along with the development of novel rapid-prototyping three-dimensional (3D) printing methods and bioprinting (3D cell printing) techniques that may allow a fabrication of customized implants for patients suffering in bone diseases in the future.
In this study, dextran-coated polyvinyl formal (PVF) sponges with high water-holding capability were developed to increase the osteogenic response in the PVF sponge. The study aimed to estimate the effect of the increased water-holding capability of the sponges on osteogenic capacity at a bone defect site in the rabbit femur epiphysis. Bone formation was evaluated using radiography, microcomputed tomography (CT), and histological analysis at 2, 4, and 6 weeks after implantation. As shown by radiography and micro-CT findings, the dextran-coated PVF sponge without water-holding capability showed little bone formation at all evaluated time points. However, the dextran-coated PVF sponge with high water-holding capability showed increasing bone formation around the implant at 4 and 6 weeks after implantation. Furthermore, as shown by micro-CT quantitative analysis, the grafted PVF sponge with high water-holding capability showed significantly greater values for percentage of bone volume per total volume and mean bone mineral density compared with the grafted PVF sponge without water-holding capability at 4 and 6 weeks after implantation. These results suggest that the dextran-coated PVF sponge with high water-holding capability promoted osteogenesis in vivo. The PVF sponge might be a new biomaterial to be used as a fill material for bone defects. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2014.
Porous Ti–15Mo alloy is fabricated by powder sintering approach from TiH2 and Mo powders. Space-holder of NH4HCO3 powder is used to regulate the pore characteristics and mechanical property. The investigation results indicate that the sintering temperature has a significant influence, while the addition of NH4HCO3 has little effect on the phase constituents of the sintered porous Ti–15Mo alloy. Pore characteristic parameters (mean pore size and porosity) and mechanical properties (ultimate compressive strength and elastic modulus under compression) of the sintered porous Ti–15Mo alloy vary with the adding amount of NH4HCO3, and match those of cancellous bones. The results indicate that it is expected to be used as a porous hard tissue implant.
This study reports the preparation of a novel porous tantalum (Ta) scaffold and the compressive property of the metallic implants. Porous Ta was produced by a thermal heat treatment method and subsequent circulating water treatments. The porous Ta scaffolds were characterized by scanning electron microscopy, quasi-static uniaxial compressive tests, and protein adsorption. It was found that the scaffold had three-dimensional hierarchical porous structures with pore size ranging from nanometer to micrometer scale. Mechanical test results showed that the scaffold has sufficient compressive strength to meet the requirements of implantation. Protein adsorption results indicated that the Ta foams are expected to be used as biocompatible implant materials.
Due to their low density coupled with excellent corrosion resistance and good mechanical properties, titanium and titanium alloys have been widely used for surgical implants. They have also a relatively low young's modulus, allowing a good load transfer to the bone. The elastic modulus difference between metallic implant material and bone is large, which can lead to a fracture of the implant. To solve this problem, many implants for artificial joint and dental applications have been produced by powder metallurgy routes, obtaining a porous material with an even lower young's modulus than that of the bulk titanium. This porous structure allows bone ingrowth, as the osseous tissue invade the holes of the porous material while growing and adheres to it. Besides, near net shape technologies like powder metallurgy and injection molding techniques, can reduce the components high costs due to machining final steps, also providing a fine, uniform grain structure and lack of texture and segregation. This work outlines the characteristics, properties and some of the powder routes for producing titanium surgical implants and implant porous coatings.
Porous Ti-Mg composites were successfully fabricated through powder metallurgy processing with ammonium hydrogen carbonate (NH4HCO3) as a space-holder. The effects of NH4HCO3 on properties of porous composites were comprehensively investigated. The pore characteristics and compressive properties of the specimens were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results show that the porosity of the porous composites can be tailored effectively by changing the amount of NH4HCO3 added, and the use of NH4HCO3 has no influence on the microstructure and phase constituents of the Ti-10%Mg porous composites. The open porosity and compressive strength as well as compressive elastic modulus vary with the adding amount and particle size of NH4HCO3. When the mass fraction of NH4HCO3 added is 25%, elastic modulus and compressive strength of composites with porosity of around 50% are found to be similar to those of human bone.
Porous
electrodes were fabricated by applying anodic pulses of
and
duration to pure Nb in phosphate buffered saline solution (PBS), aiming at biomaterial applications. The porosity of the
oxide could be controlled by the number of pulses. X-ray photoelectron spectroscopy analysis confirmed the oxide to be
. The electrochemical behavior and interfacial properties of the porous
were characterized in PBS by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS measurements
indicate that the oxide film has a two-layer structure with a compact inner layer and a porous outer layer, and the pores
were sealed by precipitates during long-time aging in PBS. The two-layer structure of the oxide film was observed by examination
of the cross section using scanning electron microscopy in backscatter mode. The CV measurements reveal that the oxide exhibits
an electrochemical “rectifying” property. It is stable over a wide potential range but shows hydrogen uptake upon cathodic
polarization below
vs
.
Porous titanium is being developed as an alternative orthopedic implant material to alleviate the inherent problems of bulk metallic implants by reducing the stiffness to be comparable to bone stiffness and allowing complete bone ingrowth. However, a porous microstructure is susceptible to local permanent plastic strain and residual stress under cyclic loading which reduces damage tolerance and therefore limits their application as orthopedic implants. The mechanical properties of porous titanium are governed by the microstructural configurations such as pore morphology, porosity, and bone ingrowth. To understand the influence of these features on performance, the macroscopic and microscopic responses of porous Ti are studied using three-dimensional finite element models. The models are generated based on simulated microstructures of experimental materials at porosities of 15%, 32% and 50%. The results show the effect of porosity and bone ingrowth on Young’s modulus, yield stress, and microscopic stress and strain distribution. Importantly, simulations predict that the bone ingrowth reduces the stress and strain localization under cyclic loading so significantly that it counteracts the concentration condition caused by the increased porosity of the structure.Highlights► Porous titanium is used as bone implant material. ► Intensive plastic bands connect closely located large pores. ► Bone ingrowth relieves the concentration of the plastic strain. ► Highly porous implant materials should consider a composite microstructure.
Titanium foams fabricated by a new powder metallurgical process have bimodal pore distribution architecture (i.e., macropores and micropores), mimicking natural bone. The mechanical properties of the titanium foam with low relative densities of approximately 0.20–0.30 are close to those of human cancellous bone. Also, mechanical properties of the titanium foams with high relative densities of approximately 0.50–0.65 are close to those of human cortical bone. Furthermore, titanium foams exhibit good ability to form a bonelike apatite layer throughout the foams after pretreatment with a simple thermochemical process and then immersion in a simulated body fluid. The present study illustrates the feasibility of using the titanium foams as implant materials in bone tissue engineering applications, highlighting their excellent biomechanical properties and bioactivity.
After endoprosthetic replacement of the femoral head, marked pathologic changes of the acetabulum, such as penetration and ulceration, often occur. These changes are caused by the rigid material surface properties of the prosthesis and the lack of damping effects. In this study, we compared the time-dependent changes of tibial articular surfaces with three kinds of femoral implant under loading conditions in dogs. Marked pathologic changes of the menisci and tibial articular cartilage were observed from 8 weeks after implantation with hard material implants, whereas the tibial joint surface against an artificial articular cartilage was still intact 24 weeks postoperatively. These results showed clearly that marked pathologic changes of the articular cartilage against rigid materials occurred and were caused by the surface properties of the counterfaces and high friction coefficients of ceramic and metal materials used. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 51–59, 1997.
OverviewIntroductionRequirements for Successful Implant SystemsOsseointegration and Bone/Implant InterfaceIntegrated Implant SystemConclusions
References
The grafting of bone in skeletal reconstruction has become a common task of the orthopedic surgeon. The need for reconstruction
or replacement is often the result of trauma, congenital malformations, or cancer. Reconstructive surgery is based upon the
principle of replacing defective tissue with viable, functioning alternatives. Various materials have been used to treat the
defects, including autogenous bone and alloplastic materials. Grafting materials are necessary to bridge defects or to increase
the bone volume. At present, autologous bone is the gold standard, but it has important disadvantages, including donor-site
morbidity, limited availability, and unpredictable resorption characteristics. These factors have stimulated the search for
other materials that can replace autogenous bone.
Bone formation and remodeling around implanted materials are influenced by the kinds of materials, surface properties of the materials, anatomical sites of implantation, and the load-bearing condition. In this study, three kinds of materials were implanted into the femoral condyles of dogs, and bone formation and remodeling were observed for 6 months. Uniform thickening of lamellar bones was observed around bead-coated alumina while thick fibrous tissues surrounded by corticalized bones formed around smooth alumina. This distinct difference in remodeling pattern was subjected to mechanical simulation by using finite-element analysis (FEA). Although stress distribution around bead-coated alumina simulates the bone density, the remodeling pattern around an uncoated implant could not be determined by the stress. To describe the latter remodeling pattern, it is necessary to analyze the strain surrounding the implants. Abundant bone ingrowth into titanium fiber under a similar loading condition was obtained 8 weeks after surgery. This ingrowth allowed firm attachment to the bones. As the tibial joint surface remained intact against polyvinyl alcohol (PVA) hydrogel, this artificial osteochondral composite material seems to be a very promising joint prosthetic material.
We investigated and compared biomechanics of natural and artificial joints. The most important functions of the joints rely on excellent lubrication and uniform distribution of impact loads on to the underlying bones. As to the lubrication, we measured dynamic changes of the joint space optically and verified the existence of fluid film lubrication in natural joints. From the aspect of fluid film lubrication, ultra high molecular weight polyethylene (UHMWPE) is not as good a material as polyvinyl alcohol hydrogel (PVA-H) and articular cartilage. The momentary stress transmitted through the specimens revealed that subchondral cancellous bones played the most important role and that UHMWPE had a higher peak stress and a shorter duration of sustained stress than articular cartilage and PVA-H, suggesting a worse damping effect. From the results of finite element method (FEM) analysis, intramedullary stem fixation might not avoid stress shielding. In artificial joints in the future, it is desirable to preserve as much subchondral cancellous bone as possible and to replace the involved joint surface with materials whose mechanical properties are similar to those of articular cartilage. We also reported biocompatibility, wear resistant properties of PVA-H, and attachment of this material to underlying bones. Although some problems still remain to be solved, PVA-H seems to be a very interesting and promising material which meets the requirements of artificial articular cartilage.
The mechanical properties of porous polysulfone (PSF) were determined and its performance as a surface coating on orthopedic and dental implants evaluated. Ten coated femoral prostheses were implanted in nine dogs. A second series of four uncoated "control" prostheses and all of the acetabular cups were implanted using conventional bone cement techniques. Six porous PSF coated tooth roots were implanted in healed mandibular premolar extraction sites in three Rhesus monkeys. The shear strength of porous PSF (6 MPa) was comparable to that of trabecular bone. Pushout tests of 1cm. thick sections of the prostheses yielded interfacial shear strength values over 1.4 MPa for the PSF coated hips after 14 weeks and mean values under 0.7 MPa for the bone cemented specimens after 3 and 36 weeks. Bone and fibrous tissue was identified in the pores of coated specimens. Preliminary clinical evaluation of the functioning dental implants revealed zero mobility and other favorable clinical and radiographic indications after 2 months.
The present status of skeletal fixation of permanent orthopedic implants by poly(methyl methacrylate) (PMMA) is discussed. It is proposed that alternatives to the acrylic cement can improve the skeletal fixation. The present paper is concerned with the fixation method by bone ingrowth into pores of the implant surface.
Two different implantation models have been designed to investigate the influence of load bearing upon ingrowth in surface pores of the implant: intramedullary nails as a means of fixation of a femoral pseudarthrosis and hinged knee prostheses. In each animal, implants with identical material characteristics (pore size, density, and thickness of the porous layer) but different loading conditions were used: one implant was “statically” loaded, the other “dynamically.” This procedure allows the evaluation of ingrowth with regard to load bearing only.
Two different mean pore sizes, viz., 87 and 110 μm, have been used with the two models. After an 8 week implantation period, bone ingrowth was evident for the statically loaded implants. Calcified tissue ingrowth was, however, not observed in the dynamically loaded implants. The discrepancy in bone ingrowth behavior between the statically and the dynamically loaded implants has been attributed to 1) the gross movement or the micromovement existing at the bone prosthesis interface and 2) the fact that the critical mean pore size for ingrowth with static loading is smaller than the one with dynamic loading.
The experimental implantations allow still another conclusion: the results suggest that designs of present clinical prostheses fixed by bone cement cannot be used with the alternative fixation by bone ingrowth unless the deisgn has been changed in a fundamental way. Mechanical factors as well as the phenomenology of bone ingrowth fixation account for this conclusion.
A series of 100 consecutive UCI knee replacements showed a 7 per cent incidence of reoperation due to loosening of the prosthesis associated with permanent deformation of the tibial component. Analysis of the clinical data, roentgenograms, and removed implants showed associations between failure and radiolucency at the cement-bone interface, prosthetic obliquity, collapse of trabecular bone, change of the alignment of the extremity, and permanent deformation of the tibial component. Although no one of these factors by itself can be responsible for the mechanical failure of the arthroplasty, a predominant failure pattern exists. We think that the sequence of events is as follows: implantation of the tibial component with medial or lateral tilt; lack of firm skeletal stabilization; continual microtrabecular fractures; change in alignment of the extremity; and permanent deformation of the plastic component.
Twenty-seven cementless total hip arthroplasties were performed in 17 steroid-dependent renal transplant patients. The average age at operation was 39 years, and the average daily dose of prednisone was 10.9 mg. At a mean of 48 months post-surgery, all patients had good to excellent hip ratings on clinical examination and the results compared favorably with 235 non-steroid-dependent age-matched patients using the identical prosthetic hip system. The results of this study suggest that long-term immunosuppression does not prevent bone ingrowth. Noncemented total hip arthroplasty appears to be a reasonable therapeutic option for end-stage osteonecrosis in steroid-dependent renal transplant patients.
The concept of bioactive ceramic coatings on macroscopically smooth prostheses tries to reconcile opposing principles: the ceramic with beneficial bone tissue growth effects is used as a coating since it does not have sufficient strength and toughness to be used by itself as a prosthesis material. But strength is still an issue since the coating is the primary means of transferring stresses from prosthesis to surrounding tissues. The interface between the metal core and ceramic surface is then critical, since it essentially depends on the strength characteristics of the ceramic. Conversely, when the ceramic coating is used as a means to enhance bone-tissue formation around and into the prosthesis surface, thereby helping to establish a mechanical form of retention, the adhesion of ceramic coating to metallic substrate is not critical. The optimum characteristics of the ceramic are then those that produce the highest effect on bone-tissue growth rates immediately after surgery. The rate of bioactivity is related to the chemical reactivity of the material causing interfacial dissolution, precipitation, and ion exchange reactions. Furthermore, it also appears to depend on a substratum function affecting mineral precipitation, collagen deposition, and cellular differentiation and proliferation.
The aim of this study was to obtain more information about the bone reaction to titanium and hydroxyapatite (HA)-coated titanium implants during the first 3 months after implantation. Therefore, uncoated and coated implants were inserted into the tibia of rabbits for various implantation periods. The histological results demonstrated that although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA-coating appeared to induce more bone formation in the medullary cavity. It was also noted, that 3 months after insertion loss of coating thickness had occurred.
The purpose of this study was to evaluate a porous biphasic hydroxyapatite-calcium phosphate ceramic as a modifier and extender of an autogeneic marrow graft for filling a 2.5-cm segmental bony defect. Twenty adult mongrel dogs were surgically treated to create diaphyseal defects in the left ulnae. The defects were (1) filled with autogeneic bone marrow mixed with granular hydroxyapatite-tricalcium phosphate ceramic (granular ceramic); (2) grafted with a solid block of ceramic soaked in autogeneic bone marrow (block ceramic); (3) received no graft (no implant); or (4) were grafted with autogeneic bone marrow alone (bone marrow). All animals were followed clinically and roentgenographically for 24 weeks and then killed. Repair of diaphyseal defects with the block ceramic led to three solid unions and three fibrous unions; with the granular ceramic implants and marrow, the defects of five dogs formed solid unions, and one progressed to a fibrous union. Defects in all five dogs grafted with autogeneic bone marrow united. The three dogs with no implant formed nonunions. Histology showed normal marrow and only a light immune reaction. Complete bridging of the defect in the dogs treated with the granular ceramic occurred significantly earlier than bridging in the dogs grafted with bone marrow alone. Histomorphometry, performed on the block ceramic implants indicated active resorption of ceramic. Clinically, addition of ceramic to a marrow graft improved the handling characteristics of the graft material and accelerated healing according to roentgenographic evaluation.
Patients with bone compromised by inflammatory arthritis and medications are often excluded from cementless total knee arthroplasty (TKA) because of concerns regarding implant fixation and ingrowth. However, many such patients are young and at long-term risk for implant failure no matter what the fixation technique. Improved implant designs and technique may improve results. Cementless arthroplasty was performed in 45 patients with inflammatory arthritis. There were 38 patients with 53 implants available for follow-up evaluation during a 2- to 6.4-year period (average, 3.3 years). Medications included steroids (16 patients), nonsteroidal antiinflammatory drugs (36 patients), and cytotoxic agents (12 patients). Twenty-nine patients were using at least two types of medication. Prostheses included the Tricon P, Tricon M, Miller-Galante, and Anatomic Modular Knee (AMK) prosthesis. The procedures were performed using standard ligament-balancing techniques. Tibial resections were within 1 cm of the tibial plateau, thereby necessitating extensive bone grafts in ten patients. Tibial components were chosen for maximal cortical rim contact. Roentgenograms were reviewed for alignment, tibial rim contact, radiolucencies, gaps, sclerosis, and subsidence. Patients with no evidence of gap or lucency had spot films under image control. Hospital for Special Surgery knee scores averaged 47 preoperatively and 88 at follow-up examination. Alignment was from 3 degrees valgus to 9 degrees valgus (average, 6 degrees valgus), with a tibial axis of 0 degrees +/- 2 degrees. Plateau coverage was within 2.4 mm (average) of the cortical rim in all planes in the anteroposterior (AP) and lateral views. Tibial sclerosis occurred with equal frequency in all AP zones and was present equally in anterior and posterolateral zones. Gaps and lucencies were more common laterally. Fifteen femoral components showed a disturbing, localized osteopenia. Sclerosis, gap, and lucency were most common anteriorly. Cementless TKA with appropriate technique can produce results comparable to cemented surgery in patients with bone quality compromised by inflammatory arthritis, steroids, and nonsteroidal and cytotoxic agents. The femoral bone response suggests an intimate bone implant relationship. The tibia shows little direct coupling of prosthesis to bone. These responses are similar to reports from other studies. Fixation is sufficient to allow for continued analysis over time and results are encouraging.
A new animal model for examining the intramedullary bone response to various implant materials and surfaces is presented, utilizing an implantable chamber with multiple bone ingrowth channels placed through a cortical defect in the lateral aspect of the distal femur. Twelve adult mongrel dogs received bilateral implants containing channels lined by smooth-surfaced coupons of titanium, titanium alloy, sputter-hydroxyapatite-coated titanium alloy, and UHMW polyethylene. A pattern was detected for all test groups of early initial bone ingrowth by two weeks, which became maximal at six to twelve weeks, followed by remodelling to a more mature lamellar bone and later resorption by 24 weeks, with fibrous tissue interfaces covering the smooth test coupons of all groups at all times. Significantly increased bone ingrowth in the sputter-HA coated group was found only at six weeks.
Total hip arthroplasty causes biomechanical changes in the normal femur, including a redistribution and concentration of stress. These mechanical alterations in the femur cause local remodeling and resorption that affect the geometry and mechanical properties of the bone. Two complementary ultrasonic techniques were used to study the local adaptive remodeling of bone due to prosthesis implantation. An ultrasonic wave propagation technique was used to determine elastic properties and a new scanning acoustic microscope (SAM) mapped the acoustic impedance profile of each section. The effects of the implantation of two types of hip prostheses, an uncemented bipolar prosthesis with an Austin-Moore type stem and a cemented Charnley prosthesis, were investigated. Both prostheses had a detrimental effect on local elastic properties as determined by acoustic velocity measurements. The SAM system provided information about local inhomogeneities in bone properties not obtainable by any other means. The acoustic impedance maps highlighted bone resorption and bone remodeling on a microstructural level.
Little consistency has been manifest among investigators in choosing an appropriate experimental model for maxillofacial bone research. In an effort to develop a protocol for the experimental analysis of maxillofacial nonunions, previous studies using calvarial and mandibular defects as models were reviewed. The creation of nonunions in animals within the calvaria and mandible was size dependent. Defects of a size that will not heal during the lifetime of the animal may be termed critical size defects (CSDs). A rationale was postulated for testing bone repair materials (BRMs) using CSDs in a hierarchy of animal models. This rationale suggests that testing should be initiated in the calvaria of the rat and rabbit, followed by testing in the mandibles of dogs and monkeys. While calvarial CSDs have been established in the rat, rabbit, and dog, further research is necessary to determine the CSD in the calvaria of the monkey, as well as the mandibles of dogs and monkeys.
High resolution microradiography and multiple fluorochrome labeling are definitive histological methods for assessing the mechanism and timing of osseous healing, maturation, and adaptation. Two fundamental types of bone interface have been described for endosseous dental implants: (1) fibro-osseous integration ("pseudo-periodontal ligament") and (2) rigid osseous fixation ("osseointegration"). No definitive bone interface studies with modern physiological methods have been reported for fibro-osseous integration. Rigid osseous fixation has been investigated in cortical bone implantation sites. The initial healing reaction involves predominantly bone modeling at the periosteal and endosteal surfaces, i.e., a woven bone callus fills with lamellae by the process of lamellar compaction. Nonvital osseous interface and adjacent compacta are replaced by bone remodeling (turnover). As assessed with high resolution microradiography, "clinically successful" specimens had less than half of the intraosseous interface in direct contact with bone. Extrapolation from animal data suggests that endosseous implants can be provisionally loaded at about 18 weeks, but full maturation of the interface requires approximately one year.
A histologic and microradiographic analysis was performed on 90 retrieved human noncemented porous-coated total joint implants recovered from 58 patients. The specimens included 62 total knee components from 34 patients and 28 total hip components from 24 patients. All components were inserted without the use of bone cement, and in no case was the retrieved component removed due to clinically or roentgenographically apparent loosening. Approximately 92% of the total knee components and 93% of the total hip components had been in situ at least six weeks; 70% of the knee components and more than 50% of the hip components had been functional for at least nine months. The histologic sections and microradiographs revealed varying amounts of bone growth into or in apposition to the porous coatings. In approximately one third of the components, no bone ingrowth or apposition was observed. No component had greater than 10% of the available porous material ingrown with bone. No relationship between the degree of bone ingrowth and the length of time in situ was noted. In all components, the majority of the porous coating contained fibrous tissue that in some cases displayed orientation indicating evidence of load transmission capability. The adherence of bony tissue at the time of removal, a positive roentgenographic evaluation, or a positive clinical presentation was not found to be a definite prognosticator of bone ingrowth. It appears that the combination of limited bone ingrowth and extensive fibrous tissue ingrowth is adequate for implant fixation.
The host response to porous-coated prostheses appears favorable; there is little evidence of any adverse tissue response or significant osteoclastic activity except in grossly loose specimens. While the nature of retrieval specimens makes any statistical correlation problematic, some generalizations can be made. Femoral hip prostheses are most likely to present bone ingrowth along the lateral quadrant of their porous coating. The frequency of bone ingrowth of femoral components was nearly twice that of acetabular devices. Pore size, geometry, and porous-coating composition did not appear to influence the appearance of bone and fibrous tissue ingrowth. Direct bonding of bone to the uncoated portion of the prosthesis was rarely seen and occurred only in closest proximity to the porous-coated regions. Indications of pain and looseness are evidence that fibrous tissue ingrowth alone is not always sufficient to ensure stability. Additionally, some bone-ingrown prostheses were retrieved because of pain, which leads to the conclusion that local bone ingrowth cannot ensure a general freedom from pain, especially with partially coated prostheses. Bone and fibrous tissue response to the porous coatings generally consists of interdigitation, while the response to uncoated regions is fibrous tissue encapsulation. Burnishing the distal tips of many of the partially coated femoral prostheses is an indication of relative motion in that region, which may be a potential source of pain.
Metallurgical and histological examinations of implants and adjacent tissue removed from orthopedic patients have been performed in a series of 190 cases. The results have been correlated with clinical findings where possible. The two major factors to emerge from this study were that many stainless steel implants corrode in the body and that titanium implants release titanium into the local tissue, which may become discolored.
Severe cases of corrosion in stainless steel implants were attributed to faulty manufacturing technique and poor implant usage. This corrosion was frequently associated with crystal‐like “microplates” in the tissue and lead to clinically significant effects in some cases. Less severe cases of corrosion were almost invariably associated with interfaces between components. Susceptibility to this corrosion may be minimised by improvements in design and materials specification.
Titanium levels in excess of 2,000 ppm were found in the tissue in 3 cases out of 19 analysed, no specimen of a control series showing greater than 100 ppm. Histological sections showed accumulations of intracellular particles of exogenous origin. The evidence that such titanium release and particle accumulation causes clinically significant effects is only minimal but it is possible that systemic distribution of titanium and remote hypersensitivity effects could arise.
A fiber titanium composite has been developed and its potential application as a method of skeletal fixation for internal prosthetic devices has been studied.
Titanium fibers, 0.19 millimeter in diameter, were cut in short lengths, compressed in dies to predetermined densities, and sintered under vacuum.
The composite exhibited adequate strength and its compliance was larger than bone.
Samples were implanted in the trochanteric and in the supracondylar areas of the femora of rabbits and dogs. Peripheral bone formation was evident at ten days, bone ingrowth was demonstrated at two weeks, and penetration deep into the samples was seen three weeks following implantation.
The shear strength of the bond at the implant bone interface in the trochanteric region of dogs was measured hs tensile tests. The strength increased significantly until the second week and remained constant thereafter until twelve weeks following implantation. Average values were in the range of 20 kg/cm2.
These findings are discussed in terms of the configuration of a prosthetic device. A fiber metal composite in the form of a thin sleeve surrounding ansd bonded to a central solid metal core would provide fixation to bone and uniform stress distribution at the implant bone interface.
When considering that the advent of the dense nonbiodegradable ceramics has been the result of new processing techniques for ceramics and that ceramics technology has made major advances through proper characterization and control of the whole manufacturing process from powder to final product, it may be apparent that other variables may be involved as well in explaining the in vivo behavior of hydroxyapatite, whether it is biodegradability or any other interaction. Physical, chemical, and crystallographic differences among so called hydroxyapatites are substantial, e. g. , vacancy density and distribution, ionic substitutional elements, powder size and shape, chemical structure of the powder surface, and adsorbants on the surface may yet be some of the more important variables. This communication shows that differences of in vivo behavior even occur within single, dense hydroxyapatite implants.
The interfacial shear properties of bone tissue growth into porous coated Ti-6-A1-4V femoral implants have been examined as a function of the pore size of the porous surface. Three particle size range powders (297 microns, 420-500 microns, 595-707 microns) were used to fabricate cylindrical implants which were inserted into the femoral medullary canal of dogs for 6 months. Push-out tests on the removed femurs are reported and reveal: (i) that those implants residing in cortical bone exhibited significantly higher shear properties than the equivalent implants in cancellous bone and (ii) that the interfacial shear strength and stiffness decreased with increasing pore diameter within the range 175-325 microns. The extent of bone ingrowth into the surface of the implants was measured using quantitative optical microscopic techniques. This indicated that the percentage of bone which had grown into the surface was inversely proportional to the square root of the pore size and that further the shear properties of the interface were proportional to the extent of bone ingrowth.
For a study on the effects of pore size variation on the rate of bone growth into porous-surfaced metallic implants and on the strength of fixation resulting from this ingrowth, 4 distinct pore size ranges were prepared on cobalt-base alloy implants with cobalt-base alloy powder particles of different dimensions. The porous implants were placed into canine femurs for periods of 4, 8, and 12 weeks. Mechanical tests were performed to measure the shear strength of fixation of the implants to cortical bone. For implants with powder-made porous surfaces, a pore size range of approximately 50 to 400 microns provided the optimum or maximum fixation strength (17 MPa) in the shortest time period (8 weeks).
A prospective clinical trial was conducted involving patients with prolapsed lumbar intervertebral disk proven myelographically, who had anterior diskectomy and disk replacement with a titanium-mesh block implant. A pilot study was done in 1971 on six patients. In this trial, 28 patients were operated on with informed consent. Twenty-three had a minimum of five years' follow-up study. There were 14 men and boys, and nine women and girls. The average follow-up period was eight years and four months (range, five to 12 years three months). The average age at operation was 36 years four months (range, 13-66 years). Symptomatic improvement were divided into three groups. Sixteen patients were in Group 1, three in Group 2, and three in Group 3. Flexion-extension radiographs showed 14 patients with no movement between the vertebral bodies adjacent to the operated disk, five with minimal movement, and four with definite movement. At the implant-bone interface, no radiolucent zone was seen in 18 patients, and a definite radiolucent zone was seen in five. Twenty implants were intact, three implants had developed a crack, and three were deformed. There were no complications. The titanium-mesh block implant is an effective substitute for autogenous bone grafting in interbody fusion.
This study evaluates the mechanical properties of a composite material comprising polyhydroxybutyrate with hydroxyapatite added in proportions varying from 0 to 50%. Among the three methods of production, injection moulding was found to result in the most satisfactory mechanical properties. The tensile and compressive strength and the modulus of elasticity of composite produced in this way fell within the range for fresh human bone from different anatomical sites. With the additional advantages of biocompatibility, biodegradability and the potential for piezoelectric stimulation of new local bone formation, it was concluded that the injection-moulded composite material has considerable potential for use in orthopaedic surgery, both as a material to construct certain orthopaedic implants and as an alternative to corticocancellous bone graft.
We have developed a new poly(vinyl alcohol) hydrogel (PVA-H) of increased physical strength through a new manufacturing process. Its mechanical properties have been found to be preferable as a substitute for articular cartilage. To evaluate its biocompatibility as an artificial articular cartilage, a series of in vivo tests within the intraarticular, as well as the intramuscular, environment were conducted. Tissue reactions of cartilage, bone, synovium, and muscle to PVA-H were studied histologically. In the experimental group, in which PVA-H was implanted, inflammatory reactions of all of these tissues were very slight. In the control group, in which ultra-high molecular weight polyethylene (UHMWPE) was implanted, although tissue reactions of bone and muscle were as slight as in the experimental group, those of cartilage and synovium were somewhat more conspicuous. By way of these findings, the better biocompatibility of PVA-H was documented.
We have attempted to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which lubrication and load-bearing mechanisms of natural and artificial joints are compared. We investigated poly(vinyl alcohol)-hydrogel (PVA-H) which has been recognized as a rubber-like gel and have improved the mechanical properties of this gel through a new synthetic process. In this article we report the biocompatibility and various mechanical properties of the new, improved PVA-H from the aspect of its usefulness as artificial articular cartilage. As regards the lubrication, we measured the change of thickness and fluid pressure of the gap formed between a glass plate and the specimen under loading and found that the PVA-H had a thicker fluid film under higher pressure than polyethylene (PE). The momentary stress transmitted through the specimen revealed that PVA-H had a lower peak stress and a longer duration of sustained stress than PE, suggesting a better damping effect. The wear factor of PVA-H was approximately five times as large as that of PE. Histological findings of the articular cartilage and synovial membranes around the PVA-H implanted for 8-52 weeks showed neither inflammatory nor degenerative changes. The PVA-H artificial articular cartilage could be attached to the underlying bone using an osteochondral composite material. Although there remain still some problems to solve, PVA-H seems to be a very interesting and promising material which meets the requirements of artificial articular cartilage.
Observations on factors controlling bony ingrowth into weight-bearing, porous, canine total hip replacements
- Jasty
Persistence of osteoblastic phenotype expression in marrow/hydroxyapatite composite
- Ohgushi
Osteogenic activity of marrow/ hydroxyapatite composite (quantitative analysis of bone formation)
- Inoue