Showing papers in "Journal of Biomedical Materials Research in 1984"

Mechanical properties of bone cement: A review

Abstract: Many authors have examined the mechanical properties of bone cement and the various factors that affect its mechanical behavior. This article presents a comprehensive survey on the reported mechanical properties of bone cement. Variables that influence the mechanical properties, such as handling characteristics, strain rate, loading modes, additives, porosity, blood inclusion, in vivo environment, temperature, etc. have also been reviewed. The importance of specifying these variables in reporting test results on the mechanical properties of bone cement is pointed out. Previous attempts to improve the mechanical properties of bone cement are also summarized. Future research areas important for fully characterizing the physical properties of PMMA are also suggested.

Surface properties determine bioadhesive outcomes: Methods and results

Abstract: This investigation developed experimental evidence for the influence of different surface energy states on tissue incorporation of biomedical materials. Implants of two smooth metals, each with three different surface energy states, were placed in the subdermal fascial plane of the backs of New Zealand White rabbits and were allowed healing times of 10 and 20 days. The implant surfaces were thoroughly characterized by physical-chemical criteria prior to surgical placement and again following removal from the tissue capsules generated by the host animals. Quantitative histopathologic analysis, using standard morphometric criteria, of the adjacent tissues revealed up to a threefold increase of fibroblastic-fibrocytic cells against the initially scrupulously cleaned, high-surface-energy materials. The cells were flattened and active, producing tenacious bonds through a thin pre-adsorbed protein-dominated "conditioning" film, that could be broken only by cohesive failure in the tissue itself. In contrast, the lower-surface-energy materials typical of standard dental implants were "walled off" by a cell-poor, nonadhesive capsule with a fibrous interface separated from a thicker "conditioning" film by a lipid-rich mucus zone. The advantages of proper surface treatment to favor the desired degree of biological adhesion are apparent.

Direct electron microscopy studies of the bone-hydroxylapatite interface.

Abstract: The bone-hydroxylapatite interface has been examined directly in the transmission electron microscope (TEM). The bone-hydroxylapatite interface was characterized by using several electron microscopy techniques, including bright and dark field imaging, electron diffraction, high-resolution imaging, and energy dispersive analysis in the scanning-transmission electron microscope (STEM EDS). Mechanical grinding followed by argon-ion milling produced interface regions of unstained and undecalcified rat bone and hydroxylapatite that were transparent to electrons. Thus the exact location of the interface could be established and the bone at the interface studied. Conventional and high-resolution imaging in the TEM demonstrated direct chemical bonding between bone and hydroxylapatite. The bone at the ceramic surface was the same as normal bone away from the interface.

Applications and failure modes of percutaneous devices: A review

Abstract: Percutaneous devices (PD) are designed to serve a variety of clinical and biomedical research purposes. Characteristically they are objects that permanently penetrate through a defect in the skin. The histological aspects of the implant skin interfacial reactions are reviewed in this article. A short description is presented of common applications of PDs. The five presently identified interfacial failure modes are described histologically with the aid of schematic drawings. These failure modes are marsupialization, permigration , avulsion, infection, alone or in combination. Single or multiple etiological factors may be responsible for these failure modes. These factors can be surgically created skin defects around the penetrating foreign implant, epidermal healing characteristics that prevent the formation of a suitable seal at the implant-skin interface and mechanical forces that may disrupt dermal attempts to seal the interface. Eventually the interface becomes infected necessitating removal of the device. Terminology recommended for use in percutaneous device research is indexed and defined.

Toxic reactions evoked by glutaraldehyde-fixed pericardium and cardiac valve tissue bioprosthesis

Abstract: Bovine pericardial tissue and tissue-derived bioprosthesis fixed in glutaraldehyde and stored in either glutaraldehyde or formaldehyde can induce cytotoxic reactions even after prolonged washing due to the slow leaching of the chemicals used for crosslinking and sterilizing. Sequential rinsing for up to 60 min was still not sufficient to eliminate cytotoxic effects. On the other hand, satisfactory results were obtained when cardiac valves made from glutaraldehyde fixed pericardium were stored in a solution containing 0.02% of propyl-hydroxy-benzoate and 0.18% methyl-hydroxy-benzoate. The valves stored in this solution and rinsed three times for 1 min in normal saline showed few signs of residual cytotoxicity. Rinsing in a solution containing glycine was partially effective in neutralizing the cytotoxic effect, and this or similar approaches offer good possibilities. The use of Chang cells grown in culture provides an excellent quantitative assay for the assessment of residual cytotoxicity and for evaluating the host response to different methods of fixation, storage, and rinsing of tissue derived bioprosthesis.

Some aspects of macrophage behavior at the implant interface

Abstract: The macrophage plays a pivotal role in both wound healing and cellular response to implants, including percutaneous devices. Within twenty-four hours macrophages were found in close contact with the implant surface. Eventually fibroplasts and connective tissue proliferate, and finally the implant will be encapsulated. The presence of macrophages is essential for the activation of collagen synthesis by fibroplasts . Implant shape and surface can profoundly affect macrophage behavior. At rough implant surfaces macrophages with giant cells are present for many months with the possibility of chronic granulomatous reactions. Superior tissue compatibility should be associated with smooth, well contoured implants with no acute angles.

Property changes of UHMW polyethylene hip cup endoprostheses during implantation.

Abstract: In this study it is demonstrated that the combined chemical and mechanical influences of the implant situation cause property changes of ultra-high-molecular-weight polyethylene (UHMW PE) hip joint cups. Nearly 30 out of 48 loosened cups, retrieved 3 weeks to 11 years after implantation, were investigated. Density measurements show a density increase with implantation time and a dependence of these changes from implant position and loading conditions. The rate of extractable constituents also increases with course of time. An increased in vivo conditioned oxidation of the UHMW PE can be demonstrated by infrared (IR) spectrometry. The density increase can be explained by post-crystallization, which is the result of oxidative chain scission. This leads to a reduction of the average molecular weight of the PE and to an increased extractability of constituents. Since these changes have been recognized as the reasons for aging and failing of UHMW PE, the methods of material characterization used in this study for retrieved implants will help to develop suitable in vitro testing and simulating methods. They are the prerequisite for the necessary improvements of the material properties of UHMW PE.

The fatigue strength of porous-coated Ti-6%Al-4%V implant alloy.

Abstract: The fatigue behaviour of Ti-6Al-4V (extra low interstital) alloy coated with Ti-6Al-4V powder was investigated using rotating bending fatigue testing. It was found that the high cycle fatigue strength of porous coated specimens exhibited a substantial decrease compared to uncoated specimens of the same microstructure. Chemical analysis of the sintered surface revealed significant increases of interstitials compared to the bulk analysis, but it is concluded that this would not adversely affect the fatigue strength. Scanning electron microscopy revealed crack initiation close to particle/substrate contact interfaces and it is concluded that stress intensification due to these interface regions are major sources of weakness with respect to fatigue strength. Finally it was found that subjecting a polished Ti-6Al-4V specimen to the heat treatment required for sintering resulted in delineation of prior beta grain boundaries and it is suggested that this also contributes to the inferior fatigue strength of porous coated Ti-6Al-4V.

In vivo metal-ion release from porous titanium-fiber material

Abstract: Dense and porous Ti, Ti-alloy, and stainless steel specimens were implanted in canine trabecular bone. After 6 and 12 months the specimens were retrieved together with bone tissue immediately adjacent. The trace metal content in the tissue samples was determined using neutron activation analysis, differential pulse polarography, graphite furnace atomic-absorption spectrophotometry, electron microprobe analysis, and laser microprobe analysis. The results are discussed in view of (i) the release of Ti ions, which is larger for porous than for bulk specimens, (ii) the various artifacts arising in electron microprobe (EMP) and laser microprobe mass analysis (LAMMA) determination of compositional gradients of trace metal-ion content in bone tissue, (iii) the absence of measurable quantities of V in bone tissue, and (iv) the difference in local tissue accumulation between Ti, released from Ti specimens, and Ni, released from stainless steel specimens.

In vivo biocompatibility studies. V. In vivo leukocyte interactions with Biomer.

Abstract: A cage implant system was utilized to quantitatively and qualitatively characterize in vivo leukocyte interactions with cast Biomer. Scanning electron microscopy (SEM) in conjunction with cytochemical staining procedures were used to investigate the cellular events at the leukocyte/Biomer interface as well as in the inflammatory exudate over a 21-day implantation period. SEM was used to characterize leukocyte morphology on the Biomer surface and the cytochemical stains were used to differentially count leukocytes and to demonstrate intracellular alkaline and acid phosphatase activity. The results showed that the population density of leukocytes on the Biomer surface diminished with implantation time. The population density of multinucleated foreign body giant cells remained constant with time, while the numbers of nuclei per giant cell increased. The differential analysis revealed that macrophages preferentially adhered to the Biomer surface compared to other leukocytes in the exudate. The phagocytic capability of all adherent leukocytes, including giant cells, decreased with time and this corresponded to changes in leukocyte morphology observed with SEM.

Difference of bond bonding behavior among surface active glasses and sintered apatite

Abstract: Three types of surface active glasses and sintered apatite were implanted in femurs of rabbits for 8 and 16 weeks and subjected to the push-out test to measure the bone bonding strength. The apatite surface layers of these materials, which were formed under in vitro treatment, were studied using IR, NMR, and AES. The difference in the bonding strength among these materials was shown statistically. The results of in vitro experiments explained the differences. It was concluded that the crystal chemistry and formation rate of the surface apatite layer significantly influenced the bonding strength. Materials that formed a surface apatite layer having a bone-like crystal chemistry and fast formation rate showed high bone bonding strength.

Fatigue properties of carbon- and porous-coated Ti-6Al-4V alloy.

Abstract: A porous metal coating applied to a solid substrate implant has been shown, in vivo, to offer advantages over current polymethylmethacrylate cement fixation in orthopedic devices. These advantages may be lost, however, in devices requiring a sintering heat treatment to apply the coating since these treatments may have a detrimental effect on the substrate material mechanical properties. In addition, more biocompatible interface coating materials have come of interest with recent literature reports of metal ion release. These coatings may be of particular use in porous-coated systems since the surface area of implant in contact with the surrounding tissues is greatly increased. This study investigated the effects that both a porous Ti- 6Al -4V alloy coating and a ULTI carbon coating have on the fatigue properties of a Ti- 6Al -4V alloy substrate system. The fatigue properties of uncoated as-received, uncoated sinter heat treated and notched Ti- 6Al -4V material were also investigated. The results of this study revealed endurance limits for Ti- 6Al -4V alloy tested with a rotating beam system of 617 MN/m2 (uncoated as-received), 624 MN/m2 ( ULTI carbon-coated), 377 MN/m2 ( sinter heat treated), 220 MN/m2 (notched) and 138 MN/m2 (porous-coated). No effects on fatigue properties were observed when testing the material in saline compared with air. The slight increase in fatigue strength for the carbon-coated material is thought to be due to the increase in surface hardness resulting from the formation of titanium carbides on the surface. The low-endurance limit of the porous-coated material is due to both the transition from the as-received equiaxed microstructure to a lamellar microstructure upon sintering and to the notch effect created by the porous coating.

The glutaraldehyde-stabilized porcine aortic valve xenograft. I. Tensile viscoelastic properties of the fresh leaflet material

Abstract: The tensile viscoelastic properties of radial and circumferential strips of fresh porcine aortic valve leaflets have been examined and compared with the fiber architecture of the leaflets as seen in the scanning electron microscope. The leaflet material showed nonlinear viscoelasticity, largely independent of strain rate, and dependent on the degree of preconditioning by cyclic loading. Preconditioning to a stable stress-strain response could only be accomplished on 1-cm-long strips above a minimum width of 4 mm (circumferential) and 6 mm (radial). Preconditioning yielded a more elastic and extensible material with reduced hysteresis. The leaflets were markedly anisotropic. Circumferential strips were up to 8 times stronger and stiffer than radial strips, and displayed greater stress relaxation and less creep. The circumferential mechanical properties were due to well-aligned circumferential collagen bundles reinforcing the composite structure, while radial properties were due to a more random collagenous support throughout the leaflet. Despite the presence of a septal shelf on the right coronary leaflet, no mechanical differences could be discerned between leaflets.

The binding of metal salts and corrosion products to cells and proteins in vitro.

Abstract: The binding of metal ions from salts and from corrosion products of 316 LVM stainless steel and MP-35 to blood cells and serum proteins was studied in vitro. In the first series of experiments, metal salts were added to whole blood and then the blood separated into red cells, white cells, and serum. Nickel from nickel chloride or corrosion products of stainless steel bound in very small quantities to blood cells. Cobalt from cobalt chloride bound to both red cells and white cells. Chromium from chromic chloride (Cr3+) bound to cells in very small quantities whereas chromium from potassium dichromate (Cr6+) and corrosion products showed very high to binding to red cells and some binding to white cells. In a second series of experiments the blood was separated into its components and then the metal salts were added and the binding pattern was identical. In a third series of experiments serum which had interacted with the metal salts or corrosion products was separated into its components by isoelectric focusing on polyacrylamide gels. Almost all of the metal, whatever the source, was detected in the albumin region of the gels indicating strong binding to albumin. These studies on the cell and protein binding of the metals help to explain the dissemination of corrosion products from the site of the implant and subsequent systemic responses by some individuals.

The glutaraldehyde-stabilized porcine aortic valve xenograft. II. Effect of fixation with or without pressure on the tensile viscoelastic properties of the leaflet material.

Abstract: We have examined the tensile viscoelastic properties of circumferential and radial strips of porcine aortic valve leaflets following fixation in glutaraldehyde and formaldehyde, with or without pressure. After aldehyde treatment, the radial strips remained weaker and less stiff than circumferential strips and responded slightly differently to the treatment. After fixation, with or without pressure, the radial strips showed large changes in stress-strain and hysteresis responses due to initial loading, and there was a twofold reduction in tensile strength and final stiffness. For strips in both directions, fixation without pressure produced doubled extensibility and a ramping stress-strain curve. Permanent (plastic) deformation of 5-20% occurred as a result of cyclic loading, stress relaxation, and creep experiments. Pressure fixation, however, produced little change in stress-strain results other than a simple shift to lower strain and produced no plasticity. Both methods of fixation reduced stress relaxation and creep. Mechanical test results are consistent with a loss of ground substance matrix during fixation. Reductions in tensile strength after fixation may be due to "riveting" of collagen geometry, producing local stress concentrations.

A canine ex vivo series shunt for evaluating thrombus deposition on polymer surfaces.

Abstract: A new acute canine ex vivo femoral A-V series shunt experiment is described. Platelet and fibrinogen deposition on a series of up to ten different polymers may be tested in the same nonanticoagulated animal. The method reduces the time and expense associated with animal testing, and also allows for the simultaneous monitoring of platelet and fibrinogen deposition on a number of polymer surfaces. The series shunt technique was used to examine platelet and fibrinogen deposition on polyethylene, Silastic, polyvinylchloride, and oxidized polyethylene surfaces. Following an initial period of minimal deposition, platelet deposition increased dramatically to a peak by about 15-20 min of blood contact on all surfaces studied. The amount of adsorbed fibrinogen fell from initial levels to a minimum at about 5-10 min of blood contact and then increased to a peak at about the same time as observed for the platelet response. Oxidized polyethylene was the most thrombogenic surface studied, followed by polyethylene, polyvinylchloride, and Silastic. Peak platelet and fibrinogen levels were found to be inversely related to flow rate over the range studied. In this experiment it appears that the interaction of blood components with a foreign surface in vivo or ex vivo is localized to the interface with the flowing blood. Within experimental errors, no effect of segment position or any downstream effects were observed. These results suggest that a series shunt may be used to investigate the short-term interactions of blood with a number of test surfaces.

Isolation of serum protein organometallic corrosion products from 316LSS and HS-21 in vitro and in vivo.

Abstract: An investigation into blood-borne organometallic compounds that arise from the corrosion of metals used in orthopedic prosthetic devices was conducted using an in vivo rat model with an implantation time of 10 days and an in vitro human serum model with an incubation time of 5 days. Both models involved 316LSS and HS-21 in the spherical powder form of 55 +/- 5 microns microns in diameter at three different surface areas to body weight ratios. Gel chromatography on cross-linked dextran (G-200) was used to fractionate the serum proteins which bound the metal ions (chromium, cobalt, and nickel) released and identify them. Atomic absorption-spectrophotometry analysis measured the concentration of the metal ions in each serum protein peak as well as whole serum from both models, and red cell and tissue from the in vivo model. Within the serum proteins, the metal ions were bound to two of the principal serum protein peaks. Similar distributions of the metals among the serum protein peaks were not noted.

Design criteria for percutaneous devices.

Abstract: A theoretical model of a percutaneous device is described. The model is split into several components, each with its own function. Special structures such as horns, hair, feathers, fingernails, hoofs , teeth, and antlers are taken as examples where nature has solved the problems of "percutaneous devices." These structures have been regarded in relation to dimensional and structural differences of epidermis, dermis, and subcutis. Theoretical guidelines are described for the design of a prosthetic percutaneous device.

Correlation of tissue reaction to corrosion in osteosynthetic devices.

Abstract: This study evaluated the interaction of osteosynthetic plates to adjacent tissue. Eleven patients had 13 plates removed with simultaneous biopsies of the adjacent soft tissue. Four patients had pain localized to the area of the plate and 11 patients had routine removal or removal for fracture nonunion. Each plate was graded on a 0-5 point scale for the amount and severity of corrosion present at the screw-plate interface. The adjacent tissue was fixed in formalin and stained with hematoxylin and eosin. The tissue reaction was graded on a 0-5 point scale based on the inflammatory response. A positive correlation of corrosion and tissue reaction was found that was significant at p less than 0.005 in the asymptomatic group. The other good correlation showed that tissue reaction tends to decrease with time at p less than 0.005. There was no correlation of corrosion with tissue reaction in the symptomatic removal group. All patients with pain adjacent to the plates were relieved by implant removal. The findings suggest that stainless steel is minimally toxic to human tissue in most circumstances and that the toxic products are well tolerated. There was a significant group (4/11) that showed a different pattern of tissue response which did not appear to be toxic response. We do not recommend routine implant removal to prevent metal toxicity; however, there is a group of patients who have pain in the area of the implant that may be caused by an allergic reaction and is relieved by implant removal.

Compressive strength of implanted porous replamineform hydroxyapatite.

Abstract: Porous replamineform hydroxyapatite is a nontoxic, nonallergenic synthetic ceramic currently under investigation as an implant for restoration of atrophic edentulous ridges. Previous studies have demonstrated its capacity to permit the ingrowth of bone into its pores. Evaluation of the material was carried out to determine its eventual compressive strength following implantation. Bony penetration results in a significant increase in strength, judged to be sufficient for support of dentures.

Water sorption in a bis(GMA)/TEGDMA resin

Abstract: Some water sorption–desorption properties of a heat-cured copolymer of bisphenol-A-glycidyl methacrylate/triethylene-glycol-dimethacrylate [bis(GMA)/TEGDMA] were investigated during three sequential water sorption–desorption cycles at 60, 37, and 60°C. The results showed that the investigated polymer absorbed almost one molecule of water for each bis(GMA)/TEGDMA molecule, causing a volumetric expansion slightly smaller than the volume of the absorbed water. The determined mean value of the sorption and desorption diffusion coefficients for a specific cycle, here named the “true” diffusion coefficient, was about 1.5 × 10−8cm2s−1 at 60°C, decreasing to one-third of that value at 37°C. Although there were differences in leaching between the two sorption–desorption cycles at 60°C, no differences in true diffusion coefficients were found during the two cycles at that temperature. However, the sorption process proceeded slower than the desorption process during the first cycle, while the opposite occurred during the second cycle. These variations could be an effect of leaching occuring during the first cycle at 60°C and also the effects of induced swelling stresses on the diffusion process.

Determination of extractable methylene dianiline in thermoplastic polyurethanes by HPLC.

Abstract: Polyurethanes are finding increasing utilization in biomedical applications. Recently, the reported finding of methylene dianiline (4,4'-diaminodiphenylmethane, MDA) in the aqueous extracts of autoclaved 4,4'-diphenylmethane diisocyanate-based polyurethanes promoted our investigation of the origin and extent of extractable methylene dianiline in polyurethanes. A high-pressure liquid chromatography procedure using precolumn derivatization is utilized to selectively monitor the appearance of this diamine in the aqueous extracts of polyurethanes subjected to water immersion, heat aging, and various sterilization techniques. No MDA was found in the aqueous extracts of the treated polyurethane except for the case of prolonged steam autoclaving. The appearance of 3-5 ppb MDA in the extract under these conditions is attributed to hydrolysis of the polymer. The stability of the polyurethanes under most conditions renders these materials useful in biomedical applications.

Equilibrium adsorption of human serum albumin and human fibrinogen on hydrophobic and hydrophilic surfaces

Abstract: The adsorption of human serum albumin and human fibrinogen on flat surfaces was quantitatively determined by measuring the decrease in UV absorption in the adsorption solution. The applicability of the method is discussed for hydrophilic and hydrophobic materials. The values of equilibrium adsorption are presented--albumin on polyethylene, and fibrinogen on polyethylene, carbon, poly(2-hydroxyethyl methacrylate), and cellophane.

Long-term compressive creep deformation and damage in acrylic bone cements.

Abstract: Compressive creep tests were performed on five commercially available acrylic bone cements under conditions simulating in vivo usage. Measured creep strains are quite large, generally exceeding elastic strains. Large variations in creep response were noted among the various cements, with a carbon-reinforced cement by far the most resistant to creep. The empirical model epsilon = a exp(b sigma)tn was found to predict creep strains within about 10% of the measured values. Microscopic examination of some specimens after testing revealed significant cracking, resulting from long-term loading, that could be a contributing cause of time-dependent failure.

The activation of the complement system by polymer materials and their blood compatibility.

Abstract: The activation of the complement system by polymer materials and their blood compatibility. One of the negative effects of the clinical application of various blood-containing biomedical devices is the activation of the complement system induced by a foreign surface. A method of determining the hemolytic activity of human serum complement before and after contact with polymers was chosen in order to elucidate the relationship between polymer surface types and the degree of complement activation. The complement activation of each donor proved to depend both on his own complement reactivity and the type of polymer surface. The role played by each constituent was estimated using the rate constants for spontaneous (ksp) and induced (kind) complement activation. The negative correlation (-0,88, p less than 0,001) between the degree of irreversible adsorption of 131I-serum albumin and relative kind was determined. Thus, we propose the use of kind for the criterion of conformational alterations of protein macromolecules induced by the adsorption/desorption processes on blood/surface interface, leading to complement activation.

Modification of polyetherurethane for biomedical application by radiation induced grafting. II. Water sorption, surface properties, and protein adsorption of grafted films

Abstract: A series of polyetherurethane films grafted by means of gamma radiation with hydrophilic or reactive monomers (2-hydroxyethyl methacrylate, 2,3-epoxypropyl methacrylate, 2,3-dihydroxypropyl methacrylate, and acrylamide) and partially chemically modified were subjected to various physico-chemical investigation methods involving water sorption, contact angle, and protein adsorption measurements. From contact angle data the interfacial free energy gamma sw between grafted films and water was calculated. It was found that the water uptake of grafted films increases with grafting yield or, in the case of grafted and afterwards chemically modified films, with reaction yield; the diffusion coefficient of water in the modified films also increases with grafting yield. Contact angle studies revealed all grafted films to have surfaces more hydrophilic than the ungrafted trunk polymer. The degree of hydrophilicity--especially of HEMA-grafted films--strongly depends on grafting conditions. For some grafted samples with high surface hydrophilicity very low interfacial free energies approaching zero were measured. The study of the competitive adsorption of bovine serum albumin, gamma-globulin, and fibrinogen from a synthetic protein solution onto modified films showed that the adsorption of albumin increases markedly with increasing grafting yields, whereas the fibrinogen and gamma-globulin adsorption only slightly increases. A correlation between interfacial free energy and protein adsorption inmore » the sense of the minimum interfacial free energy hypothesis was found only for samples with grafting yields below 5%. At higher grafting yields the increased surface area complicates the analysis.« less

Creep of conventional and microfilled dental composites.

Abstract: The creep of microspecimens of two conventional and two microfilled composites was studied using a torsional creep apparatus. Small stresses below the materials' proportional limits were maintained for 3 h and recovery was monitored for 30 h. Creep curves were obtained at 21.5, 37, and 50 degrees C, and three torque levels. The composites exhibited linear viscoelastic behavior at low deformations. The magnitude of creep depended on the amount and type of resin in the composites. The materials did not recover their original shape after 30 h after the stress was removed. No transitions were observed in the temperature range employed. The shear moduli decreased with temperature and are in reasonable agreement with literature values obtained with other tests.

On the true wear rate of ultrahigh molecular weight polyethylene in the total knee prosthesis

Abstract: The objective of this investigation was to assess the magnitude of the true wear of the polyethylene components of several total knee replacements. Five different prostheses were tested by total joint simulation for the equivalent of 1 month of use. The true wear rates of the tibial components were measured by quantitative recovery of the polyethylene debris. After testing, the tibial components were examined in the scanning electron microscope, and the molecular weight distributions were analyzed. The wear rates were found to range from 0.3 to 1.8 mg per month. The soluble fraction molecular weights ranged from 179,000 to 393,000 with 53–78% soluble. The wear rates, significantly larger than those observed for total hip prostheses, are dominated by the high contact stresses in these prostheses. The wear results in dimensional changes, which are of the same order of magnitude as those due to creep. The debris had two components: fine fibrous particles, found in all cases, and coarse granules, found when the wear rate is relatively high. Evidence for fatigue cracking was found at the surfaces of the tibial component with the highest wear rate. This behavior is consistent with other investigations of the material itself and indicates that continuous deterioration of the polyethylene should be expected in this class of prosthesis.

Release of corrosion products by F-75 cobalt base alloy in the rat. I: Acute serum elevations†

Abstract: The release of corrosion products by implants has become a matter of concern. Using a microsphere model, the release of chromium, cobalt, and nickel, secondary to implantation of various surface area exposures of F-75, a cast cobalt-chromium alloy, was studied over a 30 day period in the rat. Dose related elevations were observed in the serum concentration of chromium and cobalt but not of nickel, with the maxima being achieved at 3 days after metal implantation followed by declines in concentration. The chromium elevation, approximately twelvefold for a surface area to body weight (SA/BW) ratio of 300 X is similar to that previously reported in patients receiving total hip replacement arthoplasties . However, the cobalt elevation, twentyfold for a SA/BW ratio of 300 X, has not been previously observed. These serum concentration changes are as yet unexplained, but are probably not due to fibrous capsule maturation or alloy repassivation .