Local bisphosphonate release versus hydroxyapatite coating for stainless steel screw fixation in rat tibiae

Implant fixation in bone can be improved by a coating that delivers bisphosphonates locally, or by a hydroxyapatite (HA) coating. In this study, we compared these different types of coatings. For mechanical testing, 30 rats were assigned into three groups, and similar screws were implanted bilaterally in the proximal tibiae. The rats received screws that were either uncoated, coated with nano-crystalline hydroxyapatite or coated with a bisphosphonate releasing protein matrix. After 4 weeks, one screw was subjected to pull-out testing, and the contra-lateral one to torsion testing. For morphology, 30 rats were assigned to similar treatment groups, but received only one screw each. Bisphosphonates enhanced the pull-out force by 41% (P = 0.02) compared to controls, HA increased the pull-out force although not significantly. Conversely, HA increased the maximal torque by 64% (P = 0.02). Morphometry showed higher bone volume around bisphosphonate screws in comparison to HA-coated screws (P < 0.001) and controls (P < 0.001). The results suggest that bisphosphonates improve fixation by increasing the amount of surrounding bone, whereas HA mainly improves bone to implant attachment.     

Hydroxyapatite coating by dipping method,and bone bonding strength

Hydroxyapatite (HA) was coated onto titanium rods by a dip coating method using HA sol. The HA sols were prepared by dispersing HA crystals less than 100 nm length in distilled water or physiological salt solution using an ultrasonic homogenizer. The surface of the HA coating was homogeneous as determined by scanning electron microscopy (SEM). After implantation of uncoated and HA dip coated titanium rods in dog femurs, new bone formation was observed only around the coated material. The bone bonding strength to HA coated rods was 1.0, 1.5, 2.0 and 2.5 Mpa after 1,2,3 and 4 weeks implantation, respectively, as determined by pull-out testing. These values were over twice that of the uncoated titanium rods at 1–4 weeks after implantation. The dip coated titanium exhibited superior biocompatibility to the uncoated implant and may be of great value for bone repacement applications.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Early effect of Ti–24Nb–4Zr–7.9Sn intramedullary nails on fractured bone

A multifunctional titanium Ti–24Nb–4Zr–7.9Sn alloy (abbreviated as Ti2448) with ultra-low elastic modulus and high strength has been developed recently for potential biomedical applications. In this study, the bone healing and stability of implants in a rabbit tibial fracture model were investigated using intramedullary nails made of both the Ti2448 and Ti–6Al–4V ELI alloys. X-ray radiographic analysis showed that the volume fractions of new calluses formed around the fractured tibia increased with implantation times up to 4 weeks in both groups but no obvious difference was found between the alloys at the same time point. The micro-CT analysis revealed that, in the distal end of the tibia, there were many new calluses around nails made of the Ti2448 alloy that were confirmed by histological observations. The above analysis was consistent with tensile testing results performed 4 weeks after implantation. The mean maximum tensile force to failure of the newly formed calluses was similar between both groups whereas the mean maximum pull-out forces of the implanted nails were larger in the group of the Ti2448 alloy. Four weeks after fixation, no obvious difference in the degree of fracture healing was found between both groups. These results suggested that, in the early stage of fixation, the nails with ultra-low elastic modulus improved the new bone formation in the marrow cavity.     

Verbesserung der knöchernen Integration von Schanz’ Schrauben durch eine Poly(D,L‐laktid) Beschichtung

Improvement of bony integration of Schanz’ screws by means of a Poly(D,L‐laktid) coating Pin track infections and pin loosening are major complications in fracture treatment by means of external fixation. In this study, the influence of Poly(D,L‐lactid)‐coating on osseous integration of Schanz screws was analysed during bone healing. In sixteen sheep, osteotomies of the right tibia were stabilized by means of monolateral external fixators. In addition, mechanically unloaded Schanz' screws were inserted. One half of the implanted screws was coated with Poly(D,L‐lactid). After nine weeks in vivo, the screws were extracted, rolled on blood agar plates and microbiologically analysed, followed by histological, immunhistochemical and histomorphometrical analyses of the pin tracks. Even though no clinical signs of infection were observed, micro biological evaluation indicated a contamination by Staphylococcus aureus of 15 % in the coated screws and of 29 % in the uncoated screws. The histological analyses showed an improved osseous interagtion in the coated screws (p=0,0006) compared to the uncoated implants. In histomorphometry, the group of the uncoated screws showed an increased bone remodelling (p = 0,006) and an increased osteoclast activity (p = 0,019). Mechanically loaded screws had increased callus formation at the pin exit site (p = 0,048). The poly(D,L‐lactid) coating of Schanz' screws seems to enhance the osseous integration by reducing cortical remodelling and osteoclast activity.     

In vivo studies of the ceramic coated titanium alloy for enhanced osseointegration in dental applications

This paper reports the effect of the various ceramic coatings viz., hydroxyapatite (HA) and partially stabilized zirconia (PSZ) on the bond strength between the bone and implant, and cell compatibility of screw-shaped Ti-6Al-7Nb dental implants. Electrophoretic deposition technique (EPD) was used to obtain a uniform coating of one of the three types of ceramic layers (HA, PSZ and 50%HA + 50%PSZ) on the screws. Structural investigations were carried out on the prepared HA powder and the modified surfaces of the Ti-6Al-7Nb alloy using different techniques, namely X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The in vivo studies were performed by the implantation of screw-shaped uncoated and coated implants in the tibia of white New Zealand rabbits. To understand the bone-implant interface, biomechanical test was carried out after 2, 6 and 18 weeks healing periods. There was increased mechanical strength (torque value) of bone-implant interface with time, and the highest increment in the bond strength was recorded for implants coated with a 50% HA and 50% PSZ. Histological results show that the coated Ti-6Al-7Nb screws after 18 weeks of the implantation seem to be well-tolerated by the bone since no adverse tissue reaction was evident. However, there was a faster reaction of bone towards the coated implants compared to the uncoated one. The histochemical stain studies shows higher cellular activity and mature bone formation on all the samples.     

The immobilization of trypsin on soap-free P(MMA-EA-AA) latex particles

Poly(methyl methacrylate-ethyl acrylate-acrylic acid) latex particles with narrow size distribution and with surface carboxyl groups were produced by soap-free emulsion polymerization, and covalent immobilization of trypsin onto these particles was carried out by using the water-soluble carbodiimide (EDC) as an activating agent under various conditions. Different immobilization methods were employed and the factors affecting the efficiency and activity of the immobilized enzyme, such as the amount of trypsin and EDC, pH and temperature of the immobilization reaction were investigated. Results showed that both relatively high immobilization efficiency and high enzyme activity were achieved when pre-adsorption method was employed. The immobilization efficiency decreased as the trypsin amount increased, and increased as pH and temperature increased. When the EDC amount varied, the immobilization efficiency first increased significantly and then decreased slowly. A maximum of enzyme activity can be obtained at the optimum value of 958.0 mg trypsin/g dried particles and 372.5 mg EDC/g dried particles at 25 °C and pH 5.0. The immobilized trypsin exhibited much higher relative activity than its free counterpart.     

Influence of the coating material on the loosing of dental implant abutment screw joints

Dental implant abutment screw joints tend to loosen and prosthesis rotation has been observed under clinical conditions. Some dental implant manufacturers suggest coated abutment screw to prevent the displacement of dental prosthesis. In the present work, the opening torque (N cm) was measured as a function of tightening torque (N cm) for dental implant abutment screws coated with four different materials (TiC, TiCN, Teflon and Parylene) to clarify the influence of the coating material on abutment screw stability and to analyze the relationship between preload and opening torque. On a first series of tests, closing and opening torque (N cm) of abutment screws without coating and with coating tightened to 20, 30, 32, 35 and 40 N cm was recorded. In a second series of tests, changes in opening torque values were analyzed after successive closures that were tightened at constant values of 30, 32 and 35 N cm. On a third series of tests, abutment screws without coating and with Teflon coating were tightened to 32 N cm and submitted to cyclic loading. The results showed that for all abutment screws the opening torque was less than the tightening torque. For a given applied tightening torque (35 N cm), the screws without a coating had the highest opening torque (31.6 ± 0.9 N cm [mean ± S.D.]). The screw coated with TiN had the smallest average opening torque (12.2 ± 0.6 N cm) after tightening at 20 N cm. A progressive decrease in opening torque values was measured in all screw groups after repeated closures. After six retightenings (35 N cm) a statistically significant difference (P < .05) was observed in opening torque among uncoated Ti screw group (31.5 ± 0.6 N cm) and coated screw tested groups (Parylene = 29.6 ± 0.4, Teflon = 29.1 ± 0.7). Under cyclic loading Ti screws without coating are more stable than Teflon coated screws. The present work suggests that one must be aware of the magnitude of the opening torque when specifying a certain coating/preload combination. The present methodology shows how to calculate the relevant quantities.     

Pull-out strength of screws from cortical bone in the maxillo-facial region

The fixation of maxillofacial fractures is an important clinical procedure, which may be achieved by the attachment of plates across the fracture. The stability of the fracture will depend on the stiffness of the fracture fixation plates and the security of the fixation screws to the thin maxillofacial cortical bone. The design of screws, manufactured by Champy and AO were tested from both mini-and micro-fixation systems. Pull-out tests were conducted on cortical bone plates, ranging in thickness from 0.6 to 3.5 mm. No significant differences were observed in the ultimate pull-out forces achieved for both mini-systems of 2 mm outer diameter. However, these pull-out forces were generally greater than those obtained for the micro-screws, even at the lower bone thicknesses. Two models were developed which attempted to predict the behaviour of screw pull-out failure. The failure mechanism was primarily dependent on the thickness of the bone, with secondary influences related to the shear strength of the bone and a geometrical factor of the screw.     

Osseointegration evaluation of laser-deposited titanium dioxide nanoparticles on commercially pure titanium dental implants

The nanotechnology field plays an important role in the improvement of dental implant surfaces. However, the different techniques used to coat these implants with nanostructured materials can differently affect cells, biomolecules and even ions at the nano scale level. The aim of this study is to evaluate and compare the structural, biomechanical and histological characterization of nano titania films produced by either modified laser or dip coating techniques on commercially pure titanium implant fixtures. Grade II commercially pure titanium rectangular samples measuring 35?×?12?×?0.25?mm length, width and thickness, respectively were coated with titania films using a modified laser deposition technique as the experimental group, while the control group was dip-coated with titania film. The crystallinity, surface roughness, histological feature, microstructures and removal torque values were investigated and compared between the groups. Compared with dip coating technique, the modified laser technique provided a higher quality thin coating film, with improved surface roughness values. For in vivo examinations, forty coated screw-designed dental implants were inserted into the tibia of 20 white New Zealand rabbits’ bone. Biomechanical and histological evaluations were performed after 2 and 4 weeks of implantation. The histological findings showed a variation in the bone response around coated implants done with different coating techniques and different healing intervals. Modified laser-coated samples revealed a significant improvement in structure, surface roughness values, bone integration and bond strength at the bone-implant interface than dip-coated samples. Thus, this technique can be an alternative for coating titanium dental implants.     

Microstructural analysis of implant-bone interface of hydroxyapatite-coated and uncoated Schanz screws

The aim of the study was to compare the pin-bone interface microstructural characteristics of hydroxyapatite-coated (HAC) and stainless steel Schanz screws after 2, 4 and 6 months of implantation in a sheep model. The microstructure and composition of the hydroxyapatite coating were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Twelve coated and 12 uncoated screws were implanted into both femora of three sheep, each sheep receiving eight screws. Specimens of polished bone with screws were examined with SEM and light microscope for morphometric analyses. The HAC was approx. 40 μ m thick, the grain size ranged from 5 to 40 μ m, with pores less than 20 μ m. The atomic ratio of Ca/P was 1.62. SEM showed that the bone-implant contact was better with HAC than with uncoated implants. The ingrowth of the bone in the HAC was clearly seen. Morphometric analysis showed good bone-implant contact in 65.1 (± 24.6)% in the HAC and 32.0 (± 23.3)% in the uncoated group (p < 0.001). Although the percentage of good contact increased with time for both groups, it was significantly higher for HAC screws. Our investigation demonstrated a time dependent improvement of implant-bone contact of the HAC compared to standard stainless steel implants in the chosen experimental conditions.     

Enhanced biocorrosion resistance and biocompatibility of degradable Mg–Nd–Zn–Zr alloy by brushite coating

To further improve the corrosion resistance and biocompatibility of Mg–Nd–Zn–Zr alloy (JDBM), a biodegradable calcium phosphate coating (Ca–P coating) with high bonding strength was developed using a novel chemical deposition method. The main composition of the Ca–P coating was brushite (CaHPO₄·2H₂O). The bonding strength between the coating and the JDBM substrate was measured to be over 10 MPa, and the thickness of the coating layer was about 10–30 μm. The in vitro corrosion tests indicated that the Ca–P treatment improved the corrosion resistance of JDBM alloy in Hank's solution. Ca–P treatment significantly reduced the hemolysis rate of JDBM alloy from 48% to 0.68%, and induced no toxicity to MC3T3-E1 cells. The in vivo implantation experiment in New Zealand's rabbit tibia showed that the degradation rate was reduced obviously by the Ca–P treatment and less gas was produced from Ca–P treated JDBM bone plates and screws in early stage of the implantation, and at least 10 weeks degradation time can be prolonged by the present coating techniques. Both Ca–P treated and untreated JDBM Mg alloy induced bone growth. The primary results indicate that the present Ca–P treatment is a promising technique for the degradable Mg-based biomaterials for orthopedic applications.     

Short-and long-term neural biocompatibility of heparin coated sapphire implants

Sapphire is one of the most promising materials for the development of implantable biomedical devices due to its exceptional chemical, mechanical, electrical, thermal and optical properties. Silicon has also been widely used to manufacture neuroprosthetic devices in the past. However, both of these materials have been found to cause the most severe tissue reactions while implanted in vivo in the rat brain, compared with other biomaterials. In order to enhance the biocompatibility of sapphire and silicon, their surfaces were modified by depositing a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS), followed by the photo-immobilization of heparin. To comprehensively evaluate the short- and long-term neural biocompatibility, sapphire and silicon wafers (2.5 mm dia × 0.25 mm thick) with and without heparin coating were implanted on the surface of adult rat's cortex for 10, 28 and 90 days. Specific evaluations of the cell types that contribute to an inflammatory response were performed. The histological results indicate that the biocompatibility of sapphire is dramatically improved by heparin immobilization, while this dramatic improvement is not observed on heparin coated silicon. The failure to improve the biocompatibility of silicon by heparin immobilization can be attributed to the corrosion of the silicon surface in vivo, which was confirmed by atomic force microscopy (AFM). Meanwhile, no corrosion was observed on heparin coated sapphire surfaces and a very thin layer of proteins or extracellular matrix was deposited on the surfaces.     

Stiffness and permanent deformation of extra-articular distal tibia fractures treated with unreamed small diameter intramedullary nailing

Extra-articular fractures of the distal tibia are increasingly treated using intramedullary nailing. Due to the high load on the system and the long time of loading, fatigue phenomena have to be considered. The aim of this study is to assess the fatigue strength of the system, especially of the distal and proximal interlocking screws. Measurements were carried out using synthetic tibia bones and nails of 4 different producers. Fatigue testing was performed in three sequential stages of increasing load simulating loading during the first 6 weeks after implantation, technical loading and failure loading. The implants were characterized using the parameters stiffness, permanent deformation (including damage) and cycles to screw-failure. The results show, that highest stresses and therefore first screw damage occurred at the proximal interlocking screws. Screw-failure was observed earlier in cannulated nails and if oblique screws were used proximally.     

A histological and histomorphometrical evaluation of screw-type calciumphosphate (Ca-P) coated implants; an in vivo experiment in maxillary cancellous bone of goats

The bone response to different calcium phosphate (Ca-P) coated implants was evaluated in a goat animal model. Two types of plasma spray coatings were applied to a commercially pure titanium (cpTi) tapered, conical screw-design implant (BioComp^®); hydroxyapatite (HA-PS) and a dual coating, consisting of FA and HA (FA/HA-PS). In addition an amorphous RF magnetron sputter coating (Ca-P-a) and uncoated implants were investigated. Forty-eight implants were inserted in the maxilla of 12 adult female goats. After implantation periods of 3 and 6 months, the bone implant interface was evaluated histologically and histomorphometrically. After both implantation periods all plasma spray coated implants were maintained. On the other hand three Ca-P-a and two cpTi implants were lost. Histological examination revealed a better bone response to both plasma spray coated implants. Histomorphometrical evaluation confirmed this finding. At 3 and 6 months significantly higher percentages of bone contact (p<0.001, ANOVA) were measured for both plasma spray coated implants than for the cpTi and Ca-P-a implants, while no significant difference (p<0.05) existed between both implantation periods. Degradation of both plasma spray coatings was observed. Supported by the results, it is concluded that, although Ca-P coatings can improve the performance of dental implants, the presence of a Ca-P coating is not the only important factor for bone healing around implants placed in low density trabecular bone.     

Combinatorial coating of adhesive polypeptide and anti-CD34 antibody for improved endothelial cell adhesion and proliferation

Improved attachment, adhesion and proliferation of the surrounding mature endothelial cells (ECs) and circulating endothelial progenitor cells (EPCs) is of primary importance to realize the in situ rapid re-endothelialization of cardiovascular stents. To achieve this, a combinatorial coating of synthesized mussel adhesive polypeptide mimics as well as anti-CD34 antibody was constructed onto the devices through a novel adsorption method in this study. To immobilize the polypeptide and target antibody effectively, polycaprolactone (PCL) was first spin-coated onto the substrate as intermediate. The immobilization of polypeptide and antibody was confirmed by the changes of water contact angles and the attachment, growth of ECs and EPCs on the substrates, respectively. The results showed that after adhesive polypeptide or/and antibody immobilization, the hydrophilicity of coated PCL substrate (PCLS) was obviously improved. The amount of the immobilized antibody, determined by enzymelinked immunoassay (ELISA) method, was enhanced with the increase of antibody concentrations in the range from 5 to 25 μg/ml. The coatings after BSA blocking prevented the unspecific protein adsorption as monitored by fluorescent microscopy. The results of in vitro cell culture showed that compared with the PCLS, polypeptide/anti-CD34 antibody coating could effectively enhance the attachment, growth and adhesion of ECs and EPCs, in particular EPCs. A platelet adhesion experiment revealed that the blood compatibility of the PCLS after polypeptide/anti-CD34 antibody coating was also obviously improved. The results showed that the surface modification with adhesive polypeptide and anti-CD34 antibody will be a promising coating technique for the surface modification of the intravascular prostheses for rapid re-endothelialization.     

Fracture toughness of Kevlar-epoxy composites with controlled interfacial bonding

The fracture toughness of Kevlar-epoxy resin composites with intermittent fibre bonding of a silicone vacuum fluid (SVF-200) and a polyurethane varnish (Estapol 7008) have been studied over the temperature range –60 to 40° C and strain rates 0.03 to 5000 min^–1. Whilst both coating materials give similar tensile strengths their effects on toughness are very different. As far as toughening is concerned Estapol 7008 is more effective than SVF-200. The toughening effect increases with increasing intermittent lengths of the Estapol-7008 coating, i.e. coating parameterC, increasing temperature and decreasing strain rate. At low strain rates and high temperatures, forC=1, the toughness increase is some 200 to 300% compared to the uncoated composites. Some initial work has also been conducted for hygrothermally aged uncoated and coated fibre composites. The SVF-200 coated composites do not show any toughness degradation compared to the dry control samples. However, both the uncoated and Estapol-7008 coated composites suffer some toughness loss. Even so, the toughness of the fully coated aged specimens is as good as the uncoated dry controls. A fracture analysis is presented which gives reasonable agreement between predicted fracture toughness values and experimental measurements. It is shown that fibre pull-out toughness and fibre fracture work are the main contributors to the total fracture toughness of these fibre composites; their relative significance being dependent on the type of coating material, the temperature and strain rate of testing.     

Enhanced stability of catalase covalently immobilized on functionalized titania submicrospheres

In this study, a novel approach combing the chelation and covalent binding was explored for facile and efficient enzyme immobilization. The unique capability of titania to chelate with catecholic derivatives at ambient conditions was utilized for titania surface functionalization. The functionalized titania was then used for enzyme immobilization. Titania submicrospheres (500–600 nm) were synthesized by a modified sol–gel method and functionalized with carboxylic acid groups through a facile chelation method by using 3-(3,4-dihydroxyphenyl) propionic acid as the chelating agent. Then, catalase (CAT) was covalently immobilized on these functionalized titania submicrospheres through 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) coupling reaction. The immobilized CAT retained 65% of its free form activity with a loading capacity of 100–150 mg/g titania. The pH stability, thermostability, recycling stability and storage stability of the immobilized CAT were evaluated. A remarkable enhancement in enzyme stability was achieved. The immobilized CAT retained 90% and 76% of its initial activity after 10 and 16 successive cycles of decomposition of hydrogen peroxide, respectively. Both the K_m and the V_max values of the immobilized CAT (27.4 mM, 13.36 mM/min) were close to those of the free CAT (25.7 mM, 13.46 mM/min).     

X-ray diffraction of bone at the interface with hydroxyapatite-coated versus uncoated metal implants

The microstructural characteristics of the newly formed bone tissue at the interface with hydroxyapatite-coated and uncoated stainless steel pins used in an external fracture fixation system have been evaluated. The bone far from the interface was used as a control. Pins were transversally inserted into the diaphyses of sheep tibiae and were loaded in for six weeks. Three sheep received coated pins and two received uncoated pins. Crystallographic habit and mineralization of the implant-facing bone were evaluated. Moreover, lattice parameters of bone apatite were measured and hydroxyapatite (HA) coating degradation was investigated, by means of conventional and microbeam X-ray diffraction (XRD). In coated pins, six weeks after the implantation the newly formed bone tissue at the interface did not reach complete maturation, but the presence of the implant did not alter the apatite lattice structure; the lattice parameters did not show statistically significant variations with respect to those observed in the control bone. In uncoated pins, bone tissue rarely appeared totally mineralized and lattice parameters were significantly different with respect to those observed in the bone far from the implant. HA particles were observed spreading in the bone-facing coated pins; the XRD pattern of bone apatite surrounding HA particles was unmodified. It was concluded that HA coatings improved the bone remodelling process during pin fixation in comparison to uncoated pins and did not alter the crystallographic habit of apatite. © 1998 Chapman & Hall     

Osseointegration features of orthopedic Ti–10Si–5B implants

The present work reports on osseointegration features in rabbit tibia of orthopedic Ti–10Si–5B implants, which present a typical structure formed by the Ti and Ti₆Si₂B phases. No inflammatory reaction or rejection was noted after implantation for sixteen weeks of smooth and rough Ti–10Si–5B screw implants. Results indicated that the removal force for Ti–10Si–5B screws was continuously increased after implantation for sixteen weeks, suggesting that the bone integration process was achieved. Histological analysis revealed the occurrence of normal bone tissue growth and the presence of osteoblasts near the metal–tissue interface. Higher torque values were used to remove the rough Ti–10Si–5B screw implants after sixteen weeks, denoting that the surface treatment provided superior anchor for bone tissues. The absence of inflammatory reaction during implantation of orthopedic Ti–10Si–5B implants for sixteen weeks denotes the good bone compatibility of the composition alloy.     

Testing bone substitutes in a small animal model of revision arthroplasty

This study evaluated a modification of the rat-pin model to enable testing of bone substitute materials. The model was characterized using the ceramic, -tricalcium phosphate (TCP) as a filler. A 1 mm wide, 3.6 mm deep defect was created around a stainless steel (SS) implant in the proximal tibia of a rat. This defect was filled with a ceramic powder. Large particles (90–312m) of TCP were mixed with Gelfoam® to form a paste which was then molded around the proximal end of either an uncoated SS pin or a pin coated with hydroxyapatite (HA). The pin with its ceramic collar was then implanted into the proximal tibia of 16 male Sprague Dawley rats. Two animals with coated implants and two with uncoated implants were sacrificed at 3, 6, 14 and 26 weeks. Longitudinal sections of each tibia were stained with toluidine blue and labeled for tartrate resistant acid phosphatase (TRAP). There was initial fibrous tissue interposition around the implants which was completely remodeled around the HA coated pins but which persisted in apposition to the SS pins. The remodeling process peaked at 3 weeks around the HA coated pins and at 6 weeks around the uncoated implants. There was little remodeling around either implant by 26 weeks. There was considerable residual TCP present which was well tolerated as the particles were often encased in bone. The model has several characteristics of revision arthroplasty and the results demonstrate the suitability of this model for testing bone substitutes.An erratum to this article can be found at