The effect of silica nanoparticulate coatings on serum protein adsorption and cellular response.

Serum protein adsorption on colloidal silica surfaces was investigated using a quartz crystal microbalance with dissipation (QCM-D) monitoring. The amount of serum proteins adsorbed on colloidal silica-coated surfaces was not significantly different from the control silica surfaces, with the exception of 21nm colloidal silica which experienced significantly less (P<0.05) fibrinogen adsorption compared with control silica. The adhesion and proliferation of human endothelial cells (C11STH) on nano-scale colloidal silica surfaces were significantly reduced compared with control silica surfaces, suggesting that the conformation of adsorbed proteins on the colloidal silica surfaces plays a role in modulating the amount of cell binding. Fibronectin is one of the main extracellular matrix proteins involved in endothelial cell attachment to biomaterial surfaces. There was reduced binding of a monoclonal anti-fibronectin antibody, that reacted specifically with the cell-binding fragment, to fibronectin-coated colloidal silica surfaces compared with control silica surfaces. This suggests that the fibronectin adsorbed on the colloidal silica-coated surfaces was conformationally changed compared with control silica reducing the availability of the cell-binding domain of fibronectin.

Precipitation of hydroxyapatite nanoparticles: effects of precipitation method on electrophoretic deposition.

Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (HA) coatings on metal implants with a broad range of thicknesses, from < 1 microm to > 500 microm. As for many other HA coating techniques, densification of electrophoretically deposited coatings involves heating the coated metal to temperatures above 1000 degrees C. Metal substrates tend to react with HA coatings at such temperatures inducing decomposition at temperatures below 1050 degrees C (decomposition for pure HA normally occurs above 1300 degrees C). Therefore, densification of these coatings needs to be conducted at temperatures lower than 1050 degrees C, and this necessitates the use of high-surface-area HA nano-precipitates, rather than commercially available pre-calcined powders, which densify at temperatures typically higher than 1200 degrees C. HA nano-precipitates were prepared by three methods and deposited on metal substrates by electrophoresis: (1) the acid base method, which produced plate-like nano-particles with a 2.5:1 aspect ratio, and severely cracked coatings; (2) the calcium acetate method, which produced needle-like nano-particles with a 10:1 aspect ratio, and slightly cracked coatings; (3) the metathesis method, which produced rounded nano-particles with a 2:1 aspect ratio, and high-quality crack-free coatings. The results suggested that the less equiaxed the nano-particles, the more cracked the coatings obtained by the electrophoretic deposition technique.

Hydroxyapatite-coated metals: interfacial reactions during sintering.

Electrophoretic deposition (EPD) is a low cost flexible process for producing HA coatings on metal implants. Its main limitation is that it requires heating the coated implant in order to densify the HA. HA typically sinters at a temperature below 1150 degrees C, but metal implants are degraded above 1000 degrees C. Further, the metal induces the decomposition of the HA coating upon sintering. Recent developments have enabled EPD of metathesis-synthesised uncalcined HA which sinters at approximately 1000 degrees C. The effects of temperature on HA-coated Ti, Ti6Al4V, and 316L stainless steel were investigated for dual coatings of metathesis HA sintered at 1000 degrees C. The use of dual HA coatings (coat, sinter, coat, sinter) enabled decomposition to be confined to the "undercoat" (HA layer 1), with the surface coating decomposition free. The tensile strength of the three metals was not significantly affected by the high sintering temperatures (925 degrees C < T < 1000 degrees C). XRD/SEM/EDS analyses of the interfacial zones revealed that 316L had a negligible HA:metal interfacial zone (approximately 1 microm) while HA:Ti and HA:Ti6Al4V had large interfacial zones (>10 microm) comprising a TiO2 oxidation zone and a CaTiO2 reaction zone.

Investigation of microstructural features in regenerating bone using micro computed tomography.

We illustrate some of the uses of micro-computed tomography (micro-CT) to study tissue-engineered bone using a micro-CT facility for imaging and visualizing biomaterials in three dimensions (3-D). The micro-CT is capable of acquiring 3D X-ray CT images made up of 2000(3) voxels on specimens up to 5 cm in extent with resolutions down to 2 microm. This allows the 3-D structure of tissue-engineered materials to be imaged across orders of magnitude in resolution. This capability is used to examine an explanted, tissue-engineered bone material based on a polycaprolactone scaffold and autologous bone marrow cells. Imaging of the tissue-engineered bone at a scale of 1 cm and resolutions of 10 microm allows one to visualize the complex ingrowth of bone into the polymer scaffold. From a theoretical viewpoint the voxel data may also be used to calculate expected mechanical properties of the tissue-engineered implant. These observations illustrate the benefits of tomography over traditional techniques for the characterization of bone morphology and interconnectivity. As the method is nondestructive it can perform a complimentary role to current histomorphometric techniques.

Solution ripening of hydroxyapatite nanoparticles: effects on electrophoretic deposition.

Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (Hap) coatings on metal implants. However, densification requires heating the coated metal to high temperatures, which, for commercial HAp powders, generally means at least 1200 degrees C. At such temperatures, the metal tends to react with the HAp coating, inducing decomposition, and the strength of titanium and stainless steel implants is severely degraded. With the use of raw uncalcined nanoparticulate Hap, densification can occur at 900 degrees -1050 degrees C; however, such coatings are prone to cracking due to the high drying shrinkage. This problem was solved by precipitating nanoparticulate HAp by the metathesis process [10Ca(NO3)2 + 6NH4H2PO4 + 8NH4OH] and optimizing the approximately 30 nm of nanoprecipitates by an Ostwald ripening approach, that is, by boiling and/or ambient aging in the mother liquor. While the as-precipitated nanoparticles produced severely cracked coatings, 2 h of boiling or 10 days of ambient aging ripened the "gel-like" mass into unagglomerated nanoparticles, which produced crack-free coatings. Since boiling enhanced particle size but ambient aging did not, crack elimination probably was due to the transition from the highly agglomerated gel-like state to the dispersed nanoparticulate state rather than to particle growth. Furthermore, boiling only reduced the amount of cracking whereas aging completely eliminated cracking.

Irreversible adsorption of human serum albumin to hydrogel contact lenses: a study using electron spin resonance spectroscopy.

Human serum albumin (HSA) was specifically spin labelled with 4-maleimido-tempo (MSL) at its cysteine 34 residue (HSA-MSL). The irreversible adsorption of HSA-MSL to hydrogel contact lenses (etafilcon A, tefilcon and vifilcon A) was investigated using electron spin resonance (ESR) spectroscopy. Changes in ESR spectral characteristics of adsorbed HSA-MSL as compared to HSA-MSL in solution displayed an additional immobilisation of the spin label due to the adsorption. This immobilisation of MSL corresponds to a large conformational alteration of the HSA-MSL near the modified Cys 34 residue. For both etafilcon A and tefilcon, the rate of irreversible adsorption was relatively slow compared with that of vifilcon A where the maximum state of immobilisation and hence conformational change occurred within the first hour of adsorption. Furthermore, tefilcon produced markedly different ESR spectra where a strong conformational change to a less mobile protein was apparent. This supported a model where the direct irreversible adsorption of HSA from solution dominated on tefilcon as opposed to conversion of the adsorbed protein from the reversible to the irreversible state on both etafilcon A and vifilcon A. HSA-MSL adsorption onto hydrophobic poly(methylmethacrylate) (PMMA) and hydrophilic poly(N-ter-butylacrylamide) (PTBAM) latex beads was also investigated. The spin label MSL was found to be less mobile when HSA was adsorbed onto PMMA compared with PTBAM beads. It was also found that the rate of irreversible adsorption of HSA is far higher onto PMMA surfaces than onto PTBAM surfaces.

Nitrous acid pretreatment of tendon xenografts cross-linked with glutaraldehyde and sterilized with gamma irradiation.

Collagenous xenografts made from kangaroo tail tendon cross-linked with glutaraldehyde have a potential application in the reconstruction of massive digital tendon deficits. However, a limitation to the clinical use of these xenografts has been the optimization of collagen cross-linking, and subsequent bio-incorporation and retention of mechanical properties following implantation. The purpose of this study was to evaluate the effect of nitrous acid on modulating the biologic and mechanical properties of tendon xenografts cross-linked with glutaraldehyde. Tendon xenografts were pretreated with 0.1 or 0.01 M nitrous acid solution, prior to cross-linking in 2% glutaraldehyde and sterilization by gamma irradiation. Xenografts were implanted intramuscularly in rabbits to examine biocompatability, and also used to repair ovine digital extensor tendon deficits to evaluate functional incorporation. Histologically, intramuscularly implanted nitrous acid pretreated xenografts in rabbits had a greater degree of diffuse cellular infiltration into interstitial splits in the graft than controls after 12 weeks. Xenografts implanted in an ovine extensor tendon deficit were evaluated after 26 and 52 weeks. Rate of failure of tenorrhaphies between host tendon and xenografts overall (15/21) was significantly greater (P < 0.05) than for autografts (1/21), suggesting that the holding power of sutures in xenografts was inferior to that obtained in autografts. Tensile failure stress of midsections of both nitrous acid pretreated and control xenografts was about 100 MPa prior to implantation (time zero). After 26 and 52 weeks, failure stress of both types of xenografts was significantly less than at time zero (P < 0.05). At 52 weeks, failure stress of nitrous acid pretreated xenografts (47.4 +/- 3.1 MPa) was significantly less than control xenografts (63.7 +/- 5.4 MPa); (P < 0.05). However, nitrous acid pretreated xenografts were similar to control xenografts in failure load (357 +/- 29 and 354 +/- 26 N, respectively), but they tended to have larger cross-sectional areas (7.6 +/- 0.5 versus 5.7 +/- 0.6 mm2, respectively) which were responsible for the lower calculated value for failure stress. Histologically, autografts maintained their normal tissue architecture and evoked a more limited cellular response in surrounding tissues than xenografts (P < 0.05). Both types of xenograft were surrounded by a thicker cuff of cellular response than autografts. However, compared to control xenografts, nitrous acid pretreated xenografts had more extensive fragmentation and splitting of collagen bundles, and more diffuse cellular and vascular infiltration into these interstitial splits, and these alterations were apparently contributing to the greater 'swelling' of these xenografts. It was concluded that pretreatment of tendon xenografts with nitrous acid modulated their biologic and material properties. Further studies are needed to elucidate the mechanism of these effects, and to determine if the protocol for tendon xenograft preparation could be optimized for improved clinical performance.

Lysozyme sorption in hydrogel contact lenses.

PURPOSE: To examine the processes involved in formation of protein deposits on hydrogel contact lenses. METHODS: The adsorption and/or penetration of lysozyme on or into three types of contact lenses, etafilcon A, vifilcon A, and tefilcon, were investigated in vitro using a radiolabel-tracer technique, x-ray photoelectron spectroscopy, and laser scanning confocal microscopy. RESULTS: Binding of lysozyme to high-water-content, ionic contact lenses (etafilcon A and vifilcon A) was dominated by a penetration process. The extent of this penetration was a function of charge density of the lenses, so that there was a higher degree of penetration of lysozyme in etafilcon A than in vifilcon A lenses. In contrast, the binding of lysozyme to tefilcon lenses was a surface adsorption process. The adsorption and desorption kinetics showed similar trends to those found in human serum albumin (HSA) adsorption on lens surfaces. However, the extent of lysozyme adsorption on tefilcon is much higher than HSA adsorption, probably because of the self-association of lysozyme on the tefilcon lens surface. Furthermore, either penetration or adsorption of lysozyme involved reversible and irreversible processes and were both time dependent. CONCLUSIONS: Binding of lysozyme to hydrogel lenses involves surface adsorption or matrix penetration. These processes may be reversible or irreversible. The properties of the lens materials, such as charge density (ionicity) and porosity (water content) of the lenses, determine the type and rates of these processes.

Interfacial bond strength of electrophoretically deposited hydroxyapatite coatings on metals.

Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO3)2 + 6(NH4)2HPO4 + 8NH4OH), could produce dense coatings when sintered at 875-1000degreesC. Single EPD coatings cracked during sintering owing to the 15-18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the "valleys" in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be approximately 12 MPa on a titanium substrate and approximately 22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since -316L (20.5 microm mK(-1)) > alpha-HAp (approximately 14 microm mK(-1)), resulting in residual compressive stresses in the coating, whereas alpha-titanium (approximately 10.3 microm mK(-1)) < alpha-HAp, resulting in residual tensile stresses in the coating.

Effect of charged groups on the adsorption and penetration of proteins onto and into carboxymethylated poly(HEMA) hydrogels.

A range of carboxymethylated poly(hydroxyethyl methacrylate) (CM-PHEMA) hydrogels with varying degrees of carboxymethylation was synthesized for a systematic study of the effects of ionized groups ('charge') on the uptake by hydrogel matrices of the proteins, lysozyme and human serum albumin (HSA). Using a radiolabel-tracer technique, X-ray photoelectron spectroscopy, and laser scanning confocal microscopy, we attempted to differentiate between protein molecules that were irreversibly adsorbed onto the hydrogel surface and those that penetrated into the hydrogel matrix. The effective pore size of the CM-PHEMA hydrogels was modelled and compared with the known molecular dimensions of the two proteins. The effects of the presence of varying amounts of ionized groups in the hydrogel matrix differed for the two proteins. For lysozyme, increased uptake was observed at higher carboxymethylation; this is interpreted as resulting from a combination of electrostatic attraction and increasing ease of penetration of the protein into the more porous hydrogel matrix. For HSA, on the other hand, the uptake was primarily by surface adsorption, with little diffusive penetration into the matrix.

Interdiffusion in short-fibre reinforced hydroxyapatite ceramics.

Sintering in air and hot isostatic pressing are production methods regarded as being capable of producing fibre-reinforced hydroxyapatite ceramics for biomedical applications. These composites may have the advantage of improved mechanical properties and be suitable for applications in areas where there are significant levels of load on the material. The use of pure hydroxyapatite is restricted to those free of dynamical load. Obtaining improved mechanical strength is a question of the bond between the matrix phase and the fibre-reinforcement phase. However, a chemical bond between both phases, indicated by large diffusion zones, might lead to the dehydration of the hydroxyapatite leading to undesired tricalcium phosphate in the matrix resulting in a weakening of the mechanical and biological stability of the composites. Composites with three fibre types, alumina, 316L-stainless steel and titanium were prepared and sintered in air or hot isostatically pressed. A reaction zone was noted around the titanium and stainless steel fibres, but not around the alumina fibres. The reaction zone was larger for stainless steel than titanium. Hot isostatic pressing also reduced the reaction zone markedly compared to sintering in air.

A technique for quantitation of protein deposits on rigid gas permeable contact lenses.

PURPOSE: The purpose of this study was to develop a method for quantitating protein on rigid gas permeable (RGP) lenses and apply it to worn lenses. METHODS: We built a video microscope and wrote software to measure light absorbance by contact lenses before and after protein staining with Coomassie brilliant blue. We corrected for the temporal stability and spatial uniformity of the system, and set the iris aperture so that both lens surfaces could be simultaneously focused. We examined four RGP lens types worn by 22 patients. Standard curves were prepared with plastic discs spiked with dialyzed Coomassie blue-stained bovine serum albumin. RESULTS: The method was linear (R2 = 0.99) from 14 to over 100 microg protein per image and independent of dioptric power from -6 to +14 diopters. Protein quantities on worn Equalens II, Advent, Quantum II, and Fluoroperm 92 lenses were not significantly different (123 +/- 36, 111 +/- 28, 110 +/- 23, and 83 +/- 15 microg/lens; means +/- SEMs, P > 0.7). Patients differed (P < 0.05) in protein deposition, independently of lens type, and fit a Poisson distribution. DISCUSSION: The method is adequate for quantitating protein on RGP lenses or for examining the efficacy of cleaning regimens or care systems. However, because of the non-Gaussian distribution of patient protein deposits, paired or cross-over experimental design and testing is recommended for studying protein deposition in clinical trials.

Resorbable and non-resorbable augmentation devices for tenorrhaphy of xenografts in extensor tendon deficits: 12 week study.

Resorbable (poly-L-lactide) and non-resorbable (polyethylene terephathalate) tendon augmentation devices (TAD) in conjunction with a pericardial adhesion barrier, were designed to strengthen tenorrhaphies and were evaluated in an ovine extensor tendon deficit model in a short term study. Fifteen centimetres of tendon were resected and replaced with kangaroo tail tendon xenografts that had been cross-linked with 0.075% glutaraldehyde (GA) at 4 degrees C for one or seven days. Compared with tenorrhaphies performed with Kessler sutures alone, both types of TAD were more effective at preventing tenorrhaphy dehiscence, and thus maintaining tendon function. Furthermore, tensile strength of TAD tenorrhaphies increased significantly between zero and twelve weeks. For xenografts cross-linked in GA for one day, the tensile strength of tenorrhaphies with the resorbable TAD rose from 38 +/- 9 N at time zero, to 116 +/- 46 N at twelve weeks, while non-resorbable TAD tenorrhaphy strength at time zero was 42 +/- 16 N and 99 +/- 27 N at twelve weeks. For xenografts cross-linked with GA for seven days, similar increases in tensile strength of tenorrhaphies, with the two types of TAD were found. As there was no significant difference in mechanical performance or tissue response between the two TAD types in the first 12 weeks, use of the resorbable poly-L-lactide device may be advantageous clinically. Tensile strengths of midsections of the tendon xenograft cross-linked for 7 days was not significantly diminished 12 weeks after implantation and these xenografts were partially remodelled around the periphery. However, the tensile strength of xenografts cross-linked for one day declined significantly between time zero (319 +/- 80 N) and twelve weeks (239 +/- 92 N), suggesting that this degree of cross-linking was inadequate for maintenance of mechanical strength. Evaluation of the performance of tenorrhaphy augmentation devices with xenografts, over a longer implantation period, is required to further understand their usefulness for reconstruction of traumatic tendon injuries.

Mechanical comparison of materials used for extra-capsular stabilisation of the stifle joint in dogs.

OBJECTIVE: The mechanical properties of three materials (No. 2 polypropylene, No. 5 polybutilate-coated multifilament polyester and 18, 27 and 36 kg test monofilament nylon leader material) commonly used for extra-capsular stabilisation of the stifle in dogs with cranial cruciate ligament insufficiency were determined. The ability of No. 5 polybutilate-coated multifilament polyester and 36 kg test monofilament nylon leader material, when placed as extra-capsular sutures, to mitigate cranial drawer was evaluated in hindlimbs of cadavers. DESIGN: An in vitro mechanical study. ANIMALS: Seven pairs of hindlimbs harvested from adult greyhound dogs recently euthanased for other reasons. PROCEDURE: Samples of each material, including samples of 27 kg test leader material that had been sterilised by one of three methods (ethylene oxide, one or five cycles in an auto-clave), were loaded to determine tensile and stress relaxation properties. The effect of cyclic loading on a No. 5 polybutilate-coated multifilament polyester and 36 kg test leader material was also determined. Using the harvested hindlimbs, cranial drawer was measured before and after transection of the cranial cruciate ligament and on the first and twelfth cycle following extra-capsular stabilisation with either No. 5 polybutilate-coated multifilament suture or 36 kg test leader material. RESULTS: Leader material was found to have the most suitable mechanical characteristics for use as extracapsular stabilisation of the cranial cruciate ligament deficient stifle. Of the sterilisation methods, ethylene oxide was found to have the least detrimental effects on the handling and material characteristics of the leader material. Stifles stabilised with 36 kg test leader material had significantly less drawer than those stabilised with No. 5 polybutilate-coated multifilament polyester suture. CLINICAL IMPLICATIONS: Monofilament nylon leader material would appear to have suitable mechanical properties for extra-capsular stabilisation of the cranial cruciate ligament deficient stifle. If possible the material should be sterilised using ethylene oxide.

Stability of hydroxyapatite while processing short-fibre reinforced hydroxyapatite ceramics.

Reinforcement by short fibres has been adapted from modern ceramic processing technologies to achieve an improvement of structural properties of hydroxyapatite. However, the influence of the reinforcement fibres on the thermochemical behaviour of the hydroxyapatite has yet to be clarified comprehensively. Titanium, alumina and 316L-stainless steel, all materials with a proven record as implant materials, were chosen as reinforcement materials. Short fibres of these materials were incorporated in a matrix of hydroxyapatite to toughen the hydroxyapatite. Composites were processed by sintering in air, hot isostatic pressing and a method combining sintering in inert gas atmosphere and hot isostatic pressing.

Human serum albumin adsorption on hydrogel contact lenses in vitro.

PURPOSE: To improve the understanding of the formation of protein deposits on hydrogel lenses. METHODS: A study of protein adsorption on three commercial hydrogel contact lenses of different materials, Etafilcon A (2-hydroxyethyl methacrylate [HEMA] polymer with sodium methacrylate and 2-ethyl-2-hydroxymethyl-1,3-propanediol trimethacrylate), tefilcon (poly[HEMA] cross-linked and copolymerized with ethylene glycol dimethacrylate), and vifilcon A (methacrylic acid polymer with ethylene glycol dimethacrylate, HEMA and N-vinyl pyrrolidone) was undertaken by using a single protein solution, human serum albumin (HSA), and a radiolabel-tracer technique. RESULTS: Static adsorption leading to multilayer adsorption was observed. Complete reversibility for adsorbed HSA on lenses did not exist. Some was tightly bound, whereas most was loosely bound and could be removed easily by rinsing in phosphate-buffered saline. Irreversible adsorption of HSA on the lenses was found to be time dependent and did not reach a maximum value even after 48 hours of adsorption. The amount of HSA adsorbed on the lenses-irreversibly as well as totally adsorbed protein-was in the order of vifilcon A > tefilcon > etafilcon A. Adsorption of HSA on the lenses increases with decreasing pH (range, 7.4 to 4) but always follows the above trend with respect to the different types of lenses. CONCLUSIONS: Irreversible binding of HSA on lenses is governed by the kinetics of protein denaturation. Electrostatic interactions may not play a major role in HSA adsorption on hydrogel lenses. Some other factors, such as hydrophobic dehydration, and special monomer units, such as N-vinyl pyrrolidone in the lens materials, may favor adsorption of HSA.

Shielding of augmented tendon--tendon repair.

Strength and function of autogenic and xenogenic reconstruction of digital extensor tendons was examined in an ovine model. In this study, tendon-graft junctions were formed by either suture augmented with a woven polyester tube (A), or augmented and shielded from surrounding tissues by chemically-treated bovine pericardium (S). By 12 wk, both A and S sheep had returned to full range of motion. Mechanical strength of both the autograft-host and xenograft-host repair sites was similar, with a pooled strength of 131 +/- 25 N (n = 15). Similarly, the mid-portion xenograft strengths were constant at approximately 366 +/- 97 N (n = 7). In contrast, mid-portion autograft strengths decreased from 380 +/- 110 N (N = 4) to 120 +/- 66 N (n = 4) if shielding was omitted. The loss in autograft strength was attributed to loss of function associated with adhesions. The use of the augmentation device coupled with an adhesion barrier gives higher initial reconstruction strength and improved function during the host repair period up to 12 wk.

Sintering effects on the strength of hydroxyapatite.

Mechanisms underlying temperature-strength interrelations for dense (> 95% dense, pores closed) hydroxyapatite (HAp) were investigated by comparative assessment of temperature effects on tensile strength, Weibull modulus, apparent density, decomposition (HAp:tricalcium phosphate ratio), dehydroxylation and microstructure. Significant dehydroxylation occurred above approximately 800 degrees C. Strength peaked at approximately 80 MPa just before the attainment of closed porosity (approximately 95% dense). For higher temperatures (closed porosity), the strength dropped sharply to approximately 60 MPa due to the closure of dehydroxylation pathways, and then stabilized at approximately 60 MPa. At very high temperatures (> 1350 degrees C), the strength dropped catastrophically to approximately 10 MPa corresponding to the decomposition of HAp to tricalcium phosphate and the associated sudden release of the remaining bonded water.

Biomechanical study of canine spinal fracture fixation using pins or bone screws with polymethylmethacrylate.

Five configurations of pins or screws interconnected with polymethylmethacrylate (PMMA) were applied to isolated canine lumbar spines (L2 to L5) in which a complete fracture-luxation had been produced at L3 to L4. Twenty-five repaired spines and five intact control spines were subjected to four-point bending and tested once to failure in ventral flexion. The purpose of this study was to determine the effects of pin number, pin angle, and use of 3.5-mm cortical bone screws instead of smooth 3.2-mm diameter pins on rigidity and ultimate strength of spinal fractures repaired by the implant-PMMA fixation technique. Bending moment versus the angular deformation curves were recorded. Rigidity, bending moment at 10 degrees angular deformation, moment at failure, and deformation at failure of each type of fixation were compared using analysis of variance. Spinal segments stabilized with eight pin-PMMA fixation had significantly greater rigidity and strength at failure than four pin-PMMA fixations (P < .05). Furthermore, spinal segments stabilized with eight pins angled away from the fracture failed at significantly greater bending moment than those with eight pins angled toward the fracture (P < .05). However, for four-pin fixation, greater strength was achieved by angling pins in the bone toward the fracture site (P < .05). Screw-PMMA fixations failed by screw bending and were less rigid and weaker at failure than the corresponding configuration of pin-PMMA fixation (P < .05).

Xenografts for tendon and ligament repair.

Collagenous materials, usually of bovine or equine origin, have been popular starting points for the development of xenograft prostheses for tendon and ligament repair. Xenografts are highly attractive as they carry small risk of infectious disease, do not compromise the patient's remaining tissues and may have the 'correct' structure as the component being replaced. Animal studies, on dog, rabbit and chicken, have shown tremendous potential for this use of xenograft material as a tendon replacement. Why, therefore, have xenografts been almost universally a total failure in clinical application? The reasons would appear to be two-fold: the animal models have not been appropriate to the intended clinical use and the cross-linking of xenograft materials has not been optimized. Our work on xenograft, heterograft and autograft tissues indicates that both aspects deserve more attention. Quantitative histology indicates that the extent and type of response to xenograft materials differs widely with degree of cross-linking (glutaraldehyde). Attention must also be given to the join of the graft to the host. For both tendon and ligament the join is a site of particular fragility. Even with adequate strength in the mid-substance, tendon and ligament grafts can, and do, fail at the join. We have investigated a variety of mechanisms for joining tendon to tendon and ligaments to bone. The failures of these methods present some insight into the biology of the repair process involved and into how failure may be avoided in future.