bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wear characteristics of UHMW polyethylene: A method for accurately measuring extremely low wear rates
Authors: McKellop H. , Clarke I. C. , Markolf K. L. , Amstutz H. C. 
Published: December 2004

AbstractThe wear of UHMW polyethylene bearing against 316 stainless steel or cobalt chrome alloy was measured using a 12‐channel wear tester especially developed for the evaluation of candidate materials for prosthetic joints. The coefficient of friction and wear rate was determined as a function of lubricant, contact stress, and metallic surface roughness in tests lasting two to three million cycles, the equivalent of several years' use of a prosthesis. Wear was determined from the weight loss of the polyethylene specimens corrected for the effect of fluid absorption.The friction and wear processes in blood serum differed markedly from those in saline solution or distilled water. Only serum lubrication produced wear surfaces resembling those observed on removed prostheses. The experimental method provided a very accurate reproducible measurement of polyethylene wear. The long‐term wear rates were proportional to load and sliding distance and were much lower than expected from previously published data. Although the polyethylene wear rate increased with increasing surface roughness, wear was not severe except with very coarse metal surfaces.The data obtained in these studies forms a basis for the subsequent comparative evaluation of potentially superior materials for prosthetic joints.
In vitro corrosion of Ti‐6Al‐4V and type 316L stainless steel when galvanically coupled with carbon
Authors: Thompson N. G. , Buchanan R. A. , Lemons J. E. 
Published: December 2004

AbstractIn vitro corrosion experiments were conducted employing potentiostatic polarization techniques, a saline environment and candidate biomaterial alloy/carbon combinations. Corrosion currents and potentials of carbon/metal couples were predicted by mixed‐potential theory utilizing the polarization curves generated. The alloys examined were annealed ELI grade Ti‐6Al‐4V and cold‐worked 316L stainless steel while the types of carbon examined were LTI pyrolytic carbon and vapor‐deposited carbon. It was determined that galvanic couples of carbon to cold‐worked 316L stainless steel with carbon/metal area ratios of 10:1 to 100:1 produced coupled corrosion potentials in the range of the observed breakdown potential of the stainless steel. It was therefore predicted that localized corrosion in the form of pitting could occur on the cold‐worked stainless steel when coupled to rbon with area ratios of 10:1 or greater. The titanium alloy did not exhibit a breakdown potential up to a potential of 1.2 V. Therefore, accelerated corrosion was not predicted for the titanium alloy to carbon galvanic couples under these experimental conditions. Direct carbon/alloy coupling experiments were conducted to verify the corrosion currents and potentials predicted from mixed‐potential theory and polarization curve analysis. The experimental and theoretical values showed good agreement.
Application of auger electron spectroscopy for surface chemical analysis of avcothane
Authors: Sung C. S. P. , Hu C. B. 
Published: December 2004

AbstractThe effect of the exposure to air or to the substrate during the solvent casting process on the surface chemical composition of Avcothane, a blood compatible biomaterial, was studied by employing Auger electron spectroscopy. The surface layer of 10–15Å thickness was analyzed without sputtering, but for the studies probing a deeper layer, argon ion sputtering at a low enough voltage to prevent artifacts was utilized.It is found that the air facing surface which is the blood contact surface contains a greater amount of silicone polymer and a much lower amount of the urethane hard segment in the first 10–15Å‐deep layer than in the comparably thick layer of the substrate surface. However, the depth‐composition profile obtained by sputtering indicate that, probably at a deeper depth, the chemical compositions in terms of silicone polymer and hard segment is comparable both in the air side and the substrate side.
Direct anchorage of Al2O3‐ceramic hip components: Three years of clinical experience and results of further animal studies
Authors: Heimke G. , Griss P. , Jentschura G. , Werner E. 
Published: December 2004

AbstractThe biocompatibility of high‐purity dense Al2O3‐ceramics had been shown to open the possibility of direct cement‐free anchorage of joint endoprostheses. Three years of clinical experience with ceramic‐metal composite total hip prostheses confirm the biomechanical design criteria used for the acetabular components. They also allow for additional conclusions regarding the reaction of bone tissue towards a bioinert implant. Further research activities are directed towards a solution for the biomechanically stable anchorage of the femoral component of hip prostheses.
A method for toxicity screening of biomaterials using cells cultured on millipore filters
Authors: Wennberg A. , Hasselgren G. , Tronstad L. 
Published: December 2004

AbstractIn the present paper a tissue culture technique is described whereby the toxicity of setting and solid materials may be evaluated. A cell monolayer was established on a millipore filter which was placed on an agar medium, cell side down. Test specimens were placed on top of the millipore filter and were allowed to influence the cells through the filter for two hours. The cell reaction was assessed by incubating the cells, still adherent to the filter, for the demonstration of succinate dehydrogenase activity. Materials with a cytotoxic effect caused a zone of inhibited enzyme activity in the cell‐material contact area. The filters were examined macroscopically and scores from 0 to 3 were given to grade the severity of the cell response. Unset and set silicate cement, zinc phosphate cement and an acrylic resin were tested. The results obtained were consistent and in accordance with those of previous reports. The method was simple and rapid and appeared suitable for the assay of larger test series.
A study of the reaction of human tissue to proplast
Authors: Halstead A. , Jones C. Wynn , Rawlings R. D. 
Published: December 2004

AbstractThe femoral stems of Thompson prostheses coated with a polytetrafluoroethylene/carbon fiber composite (proplast) were studied using conventional histological examination, scanning electron microscopy and electron probe microanalysis in “successful” firm implants and in a “loose” clinically unsuccessful implant. Ingrowth was found throughout the coatings of the successful prostheses. In the most firmly fixed prosthesis the ingrowth consisted of fibrous tissue with abundant giant cells; however, no bone ingrowth was detected. There was less composite pore infilling in the unsuccessful implant. From both clinical, radiological and the studies described above, it is concluded that fibrous tissue ingrowth was a secondary stabilizing phenomenon in the proplast‐coated prostheses studied.
Monomer release from methacrylate bone cements during simulated in vivo polymerization
Authors: Schoenfeld C. M. , Conard G. J. , Lautenschlager E. P. 
Published: December 2004

AbstractThe release of monomer from methylmethacrylate bone cements was studied during immersion in an aqueous environment intended to simulate in vivo polymerization of the material. Monomer release from disk‐shaped specimens into an aqueous environment was assayed by gas chromatography. The simulated intracorporal polymerization was carried out under a variety of conditions intended to encompass possible clinical variables. The majority of monomer release occurred within the first 15 min of immersion. Under conditions generally recommended for commercial cements the release into aqueous media was always less than 3% of the total monomer weight. Clinically feasible options of delaying the time from onset of mixing of the cement to insertion into the host resulted in only a 0.7 wt % difference in the amount of released monomer. Measurements for a variety of monomer/powder ratios demonstrated a minimum in the amount of released monomer at a ratio of about 0.4 ml/g. In terms of unit area covered, thin specimens released less monomer than thick specimens.
Surface charge in foreign body carcinogenesis
Authors: Andrews Edwin J. , Todd Paul W. , Kukulinsky Nancy E. 
Published: December 2004

AbstractThe importance of surface charge in foreign body carcinogenesis was evaluated by implanting in C3H/HeJ male mice, bipolar polystyrene thermoelectrets formed in variously charged electrical fields. Charged electrets had tumor rates similar to control groups. The cumulative probability of tumor development was highest in the charged electret group being 0.58 at 133 weeks after implantation. The tumor rate for all charged electrets was 27% as compared to 17% and 6% for the control groups. The latent period of tumor induction varied little between groups and averaged approximately 700 days. No conclusions regarding the tumorigenic effect of electropositive versus electronegative (body) sides of the electret. An occasional tumor (2/25) arose on both sides of a single electret. The antigenicities of tumors tested by excise and challenge techniques were weak. The immunologic relationship between top and bottom growing tumors on a single electret could not be adequately determined because of the weak antigenicity.
Solution treatment behavior of Co‐Cr‐Mo alloy
Authors: Clemow A. J. T. , Daniell B. L. 
Published: December 2004

AbstractCurrent practice in the manufacture of Co‐Cr‐Mo alloy total hip prostheses is the use of a solution treatment to increase the ductility of the as‐cast alloy. This study is concerned with the reactions encountered during solution treatment at temperatures between 1165–1270°C. These reactions, including incipient melting, a carbide transformation from M23C6 to M6C and sigma‐phase formation, have bene examined using both qualitative and quantitative metallographci techniques, and are shown to influence the production of a single phase microstructure. As a res8lt, an optimum temperature for solution treatment of 1220°C has been determined. It is futher proposed that a reduction in the carbon content of this alloy would improve its solution treatment behavior.
In vitro deformation failure analysis of dental amalgams
Authors: Vaidyanathan T. K. , Schulman A. 
Published: December 2004

AbstractThe in vitro deformation failure behavior of the conventional and the recent high copper dental amalgams is studied under different strain rates. The conventional silver‐tin amalgams exhibited significant slow compressive flow at low strain rates, but failed catastrophically at the higher loading rates. On the other hand, amalgams containing highest copper contents showed no compressive flow and failed ctastrophically at all the loading rates. The slow compressive flow in the conventional dental amalgams indicate that dislocations may play an important role in the deformation process of the amalgams at the lower strain rates.
Bioevaluation of plasma polymerized films in skeletal muscle
Authors: Nichols Michael F. , Hahn Allen W. , Roger Easley J. , Mayhan Kenneth G. 
Published: December 2004

AbstractPlasma polymerized ethylene (PPE), styrene (PPS), and chlorotrifluoroethylene (PPCTFE) were synthesized by exposing the monomeric gases to an inductively coupled radio frequency “glow‐discharge” field. The polymer films were deposited on poly(dimethyl) siloxane (medical grade Silastic®), which was then surgically implanted in rat paravertebral muscle for periods up to 84 weeks. The biocompatibility of the plasma deposited films and uncoated Silastic® was evaluated by qualitative (graded inflammatory cell response) and quantitative (connective tissue capsule thickness) techniques as a function of time. The morphological features of the connective tissue capsule and the plasma polymerized films were examined by SEM after 75 weeks of implantation. Results showed that the acute inflammatory cell migration around PPS and PPCTFE was at a maximum in 2 weeks, decaying to control levels in 4 to 8 weeks. The PPE response was judged as less than the control response up to 4 weeks. After 8 weeks no qualitative difference could be detected between the plasma polymerized films and Silstic®. On the other hand, a quantifiable change in fibrous capsule response as a function of time and material was noted until 24 weeks. From these data we conclude that these types of films do not elicit an untoward foreign body reaction at a skeletal muscle implant site in rats.
Effect of an in vivo environment on the strength of bone cement
Authors: Rostoker W. , Lereim P. , Galante J. O. 
Published: December 2004

AbstractBar‐shaped polymethylmethacrylate test specimens removed from rabbits after implantation for times up to 26 months showed a significant change in fracture stress as determined by three‐point bending in the period between 12 and 26 months. There were no adverse findings in the tissue which developed around the bone‐cement test bars.
13C NMR spectroscopic analysis of poly(electrolyte) cement liquids
Authors: Watts David C. 
Published: December 2004

Abstract13C NMR spectroscopy has been applied to the analysis of carboxylic poly‐acid cement liquids. Monomer incorporation, composition ratio, sequence statistics, and stereochemical configuration have been considered theoretically, and determined experimentally, from the spectra. Conventionally polymerized poly(acrylic acid) has an approximately random configuration, but other varieties may be synthesized. Two commercial glass‐ionomer cement liquids both contain tartaric acid as a chelating additive but the composition of their poly‐acids are different. Itaconic acid units, distributed randomly, constitute 21% of the repeating units in one of these polyelectrolytes.
The influence of final mercury content on the characteristics of a high‐copper amalgam
Authors: Mahler David B. , Adey Jerome D. 
Published: December 2004

AbstractIn this study, specimens of a high‐copper amalgam, prepared at different final Hg contents, were examined in several different experiments. The results showed that as the Hg content is increased, a point is reached beyond which creep and the amount of Sn in γ1 exhibit a sudden increase. As the Hg content is increased further, γ2 can be detected. These phenomena can be explained by the hypothesis that insufficient Cu is present at higher Hg contents to combine with Sn to form Cu6Sn5.
Effect of implant surface chemistry upon arterial thrombosis
Authors: Van Kampen C. L. , Gibbons D. F. , Jones R. D. 
Published: December 2004

AbstractA series of poly(α‐amino acid)s with controlled chemical variations were investigated in order to assess the effect of different chemical moieties upon arterial thrombosis. The gross implant surface properties ranged from hydrophobic to hydrophilic, ionic and nonionic. The materials were tested by implantation within canine femoral and carotid arteries. Results were compared with the response to the polyurethane Biomer.The changes in implant surface chemistry elicited a range of response that varied from intense thrombosis and rapid vessel occlusion to minimal thrombosis and endothelialization. The results showed that no simple relationship exists between a gross surface property, such as hydrophobicity, and the degree of thrombosis resistance. Some hydropobic and hydrophilic materials were found to have good thrombosis were shown to play and hydrophilic materials were found to have good thrombosis were shown to play an important role in both initial thrombosis and endothelialization. The major difference between materials that progressed to to rapid vessel occlusion and materials that remained patent was the degree of direct leukocyte adherence and spreading on the implant surface prior to extensive platelet aggregation (<30 min). It was consistent for both hydrophobic and hydrophilic materials that the lack of direct leukocyte adherence to the implant surface was associated with intense thrombosis and rapid vessel occlusion. Conversely, the presence of numerous leukocytes directly adherent to either hydrophobic or hydrophilic surfaces appeared to have a moderating effect upon thrombosis and vessels with these implants remained patent. In instances when thrombosis was nonocclusive, the surfaces of the thrombi became endothelialized, primarily through the transformation of mononuclear leukocytes into endothelial cells. This article includes a hypothetical model representing the sequence of events and alternative pathways occurring at the blood‐material interface, with special attention given to the involvement of leukocytes in arterial thrombosis.
Transient in vivo protein adsorption onto polymeric biomaterials
Authors: Ihlenfeld Jay V. , Cooper Stuart L. 
Published: December 2004

AbstractThe adsorption of albumin, γ‐globulin, and fibrinogen was measured on three ex vivo polymeric shunt surfaces [polyvinyl chloride (PVC), Silastic, and segmented polyether urethane (Biomer)] exposed to flowing heparinized, canine blood in vivo. Small amounts of radiolabeled proteins were infused into anesthetized mongrel dogs and the deposition of radioactivity on the walls of femoral arteriovenous shunts was followed with time for two hours following initial blood‐polymer contact.Previously, transient in vivo platelet and fibrin deposition onto PVC, Silastic, and Biomer was measured by a similar technique in the absence of anticoagulant. A time‐dependent phase of thrombus deposition followed by thromboembolism was observed on the PVC and Silasticshunt surfaces but not on the Biomer surface. In the studies reported here on PVC and Silastic, fibrinogen adsorption was found to predominate initially, though it subsequently desorbed somewhat and was replaced by albumin and γ‐globulin. On Biomer, the adsorption of all three proteins increased with time following initial blood contact and fibrinogen was less prominent initially. The PVC surface was found to become passivated with respect to further thrombogenesis after 60‐min exposure to flowing blood, at which time a higher fraction of albumin was present on the surface compared to that at earlier blood contact times. These results indicate that rearrangement of adsorbed protein species occurs with time on polymer surfaces exposed to flowing blood in vivo. Early and predominant fibrinogen adsorption appears to be an important factor in the thrombogenic and embolic events observed on the PVC and Silastic shunt surfaces in vivo.
Grafting of proteins onto polymer surfaces with the use of oxidized starch
Authors: Ikada Y. , Iwata H. , Mita T. , Nagaoka S. 
Published: December 2004

AbstractA study has been carried out on the coupling of proteins onto crosslinked poly(vinylalcohol) hydrogel membranes and ethylene‐vinyl alcohol copolymer(EVA) films pre‐viously grafted with oxidized starches having many pendant aldehyde groups. The coupling reaction of proteins is based on the Schiff's base formation between the amino groups of proteins and the aldehyde groups of the oxidized starches which have been grafted onto the substrate membrane or film through acetalization of the aldehyde of starch with hydroxyl groups of the substrate polymers. The grafting of oxidized starches onto the EVA films seems to be restricted to the film surface, since no detectable change is observed in the weight and the attenuated total reflection infrared spectrum of the grafted films. The amount of grafted protein, determined by the ninhydrin method, reveals that, at least, plasma proteins such as serum albumin and fibrinogen are grafted to the film surface in a monomolecular layer without undergoing a marked denaturation. The α‐amylase grafted onto the EVA film showed a distinct enzymatic activity in hydrolysis of amylose and starch, but the activity was very low compared with that of the ungrafted, soluble α‐amylase.
Characteristics of tissue growth into proplast and porous polyethylene implants in bone
Authors: Spector M. , Harmon S. L. , Kreutner A. 
Published: December 2004

AbstractOne objective of this study was to determine why fibrous tissue, not bone, forms in internal pores of Proplast implants even though the material is labeled as having pore characteristics compatible with bone ingrowth. A second objective was to assess the suitability of the fibrous tissue in Proplast implants for supporting load‐bearing prostheses. Thirty cylindrical rods of Proplast were implanted through the lateral diaphyseal cortex of eight dogs for periods of 1 to 20 weeks. Porous high density polyethylene was used as a „control”︁ in the study since it is a low modulus polymer which does undergo bone ingrowth. Twenty rods of porous polyethylene (400 μm average pore size) were implanted in the experimental animals along with the Proplast. Postmortem specimens were prepared for microradiography and histological evaluation. Optical point‐counting techniques and mercury intrusion porosimetry were used to determine the pore characteristics of the materials. Microradiography and histological evaluation revealed bone growth throughout the porous polyethylene implants. In contrast, bone growth was only occasionally observed in surface pores of the Proplast. However, bone completely filled Proplast specimens which were teased to purposely enlarge the pores of the material prior to implantation. This observation, along with the pore analyses which revealed an average pore size of only 75 μm and interconnecting pores less than 50 μm in diameter, led to the conclusion that fibrous tissue, not bone, forms in Proplast specimens because of the small pore size of the material. Further, the results demonstrated that there was no collagen continuity of the fibrous tissue in the pores of the material with surrounding bone (e.g., no Sharpey' fibers) suggesting that the load‐bearing support which can be afforded by Proplast implants is limited by the incomplete bone ingrowth along the margins of the material and the tensile strength of Proplast.
Behavior of three high‐Cu amalgams
Authors: Mahler David B. 
Published: December 2004

AbstractAmalgams made from three single‐composition high‐Cu alloys of the same nominal composition were investigated for differences in creep behavior. The curves of creep vs. final Hg content for all three alloys showed a sudden creep increase (jump) at approximately 46% final Hg content. Previous studies have shown this creep jump to be associated with the initiation of the SnHg phase (γ2). The anticipated final Hg content in clinical restorations for two of these alloys is below the creep jump and γ2 would not be expected. On the other hand, the clinical Hg content for the third alloy was above its creep jump and γ2 would be expected. The effect on clinical behavior of this finding requires further investigation.
SEM fractorgraphy studies of porous vitreous carbon: A candidate biomaterial
Authors: Tarr Richard R. 
Published: December 2004

AbstractA new porous vitreous carbon material under development for use in orthopedic applications was investigated. Specimens were machined to appropriate sizes and fractured in one of the following modes: compression, cantilevered bending, or axial torsion. Scanning electron microscopy (SEM) was used to examine surface and internal features. Characteristics of a brittle, glassy material were noted. Findings included internal voids which appeared as craters, patches of whiskerlike fibrils, and edge impurities. Numerous microcracks caused by mechanical shaping and handling were the most remarkable structural defects. Pore channels which would allow bony in growth ranged in size from 50–500 μm with the majority between 200 and 300 μm. This study of porous vitreous carbon points to the need for stricter quality control in manufacturing, alternative methods for shaping and handling, and careful consideration in design and usage of a brittle material with marginal limits of safety for biomedical applications.