bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite element temperature analysis of a total hip replacement and measurement of PMMA curing temperatures
Authors: Swenson Lyle W. , Schurman David J. , Piziali Robert L. 
Published: December 2004

AbstractAnalytical and experimental studies were performed to examine some characteristics of poly(methyl methacrylate) bone cement in the context of total hip replacement. Proceeding from fundamental principles of balance of energy and heat conduction, three simulation models of total hip replacement, using the finite‐element method of numerical analysis, were used to predict the temperature response in the femoral prosthesis, cement, cancellous bone, and bone‐cement interface. When cement collars are a centimeter or less in thickness, the models predict little likelihood of permanent bone thermal necrosis. In addition, laboratory experimental results indicate that peak temperatures attained in Simplex‐P and Palacos‐R cement specimens are nearly identical and that adding 0.5 and 1.0 g of the antibiotic gentamicin to Palacos‐R has negligible influence on peak temperature. Experimental results also indicate that cooling cement specimens to 8°C extends the set time, which in turn could significantly increase the likelihood of stemcement loosening during surgery.
Piezoelectric ceramic implants: in vivo results
Authors: Park J. B. , Kelly B. J. , Kenner G. H. , von Recum A. F. , Grether M. F. , Coffeen W. W. 
Published: December 2004

AbstractThe suitability of barium titanate (BaTiO3) ceramic for direct substitution of hard tissues was evaluated using both electrically stimulated (piezoelectric) and inactive (nonpolarized) test implants. Textured cylindrical specimens, half of them made piezoelectric by polarization in a high electric field, were implanted into the cortex of the midshaft region of the femora of dogs for various periods of time. Interfacial healing and biocompatibility of the implant material were studied using mechanical, microradiographical, and histological techniques. Our results indicate that barium titanate ceramic shows a very high degree of biocompatibility as evidenced by the absence of inflammatory or foreign body reactions at the implant‐tissue interface. Furthermore, the material and its surface porosity allowed a high degree of bone ingrowth as evidenced by microradiography and a high degree of interfacial tensile strength. No difference was found between the piezoelectric and the electrically neutral implant‐tissue interfaces. Possible reasons for this are discussed. The excellent mechanical properties of barium titanate, its superior biocompatibility, and the ability of bone to form a strong mechanical interfacial bond with it, makes this material a new candidate for further tests for hard tissue replacement.
The quasistatic and fatigue performance of the implant/bone‐cement interface
Authors: Raab S. , Ahmed A. M. , Provan J. W. 
Published: December 2004

AbstractLoosening is a major cause of failure in total arthroplasties. The efficacy of the fixation systems depends not only on the bulk properties of the components but also on the interfaces through which they interact. This study was initiated to examine the implant/bone‐cement interface for four of the most commonly used implant materials, CoCrMo, Ti6Al‐4V, 316SSLVM and ultrahigh molecular weight polyethylene (UHMWPE). The surface preparation, specimen design, joining, and testing techniques were studied and then standardized in a manner which accurately represents current clinical procedures. The interfaces were tested for both their quasistatic and fatigue properties. Finite‐element and fracture toughness analyses of the quasistatic shear specimens were performed in order to provide results of an absolute nature which could be subsequently compared to bulk material properties of bone cement. The interfaces were tested “dry” (i.e., at room temperature and 50% R.H.) and in physiological saline at 37°C. The interfaces demonstrated both fracture toughness and fatigue properties far inferior to those of bone cement. A predominantly interfacial type failure was observed using SEM fractography. The ultimate compressive strength (U.C.S.) of bone cement was measured after prolonged exposure to saline at 37°C and showed no decrease in U.C.S. suggesting that the reasons for the interface strength reductions were interfacial rather than bulk in nature. The “wetting'” ability of bone cement was measured using contact angles at various cure times on the four implant materials. These measurements showed that intimate interfacial contact is impossible with current clinical methods. This study indicates that failure of the implant/bonecement interface is likely only a short period after implantation and therefore may be a major contributor to implant loosening.
Pressurized polymerization for reaction casting of poly(2‐hydroxyethyl methacrylate)
Authors: Pinchuk Leonard , Eckstein Eugene C. 
Published: December 2004

AbstractHomopolymers of the hydrogel poly(2‐hydroxyethyl methacrylate) are produced with no observable bubbles trapped in the lattice by performing the free radical initiated polymerization reaction under pressure (700 kPa). Implantable hydrogel structures of intricate and exact geometry, such as nipples for ureteral anastomoses in the prosthetic urinary bladder, can be made using this technique.
Mechanical properties of poly(methyl methacrylate) bone cements
Authors: Robinson R. P. , Wright T. M. , Burstein A. H. 
Published: December 2004

AbstractSamples of low viscosity poly(methyl methacrylate) (PMMA), graphite reinforced PMMA, and graphite reinforced low viscosity PMMA were evaluated for their compression strength and fracture toughness. These results were compared with two currently used plain PMMA bone cements. There were no statistically significant differences in compression strength between the five cements. Graphite reinforcement of plain cement produced a 32% increase in fracture toughness over plain cement. Graphite reinforcement of low viscosity cement also produced a significant increase in toughness (31%) over low viscosity cement with fiber reinforcement. However, low viscosity cement demonstrated significantly less fracture toughness than plain PMMA.
Effect of radiation sterilization and aging on ultrahigh molecular weight polyethylene
Authors: Roe Ryong‐Joon , Grood Edward S. , Shastri Ranganath , Gosselin Cynthia A. , Noyes Frank R. 
Published: December 2004

AbstractThe mechanical properties of polyethylene components used in prosthesis are altered after fabrication by the sterilization procedure and by the environmental and mechanical aging which occurs after implantation. To assess the importance and extent of these alterations, ultrahigh molecular weight polyethylenes from two sources, Hercules 1900 and RCH 1000C, were subjected to gamma‐ray irradiation and aging in serum and argon environments. Changes induced by these treatments in the structural and mechanical parameters have been determined by a variety of experimental techniques. The effect of irradiation is to introduce crosslinks and to increase the degree of crystallinity resulting in changes in the tensile properties in the direction of higher stiffness and reduced ductility. Aging for six months produced similar changes with subtle differences. The results suggest that the initially low degree of crystallinity which results from the sluggish mobility of the very long chain molecules offers the opportunity for significant changes in the properties during use in the long run.
Biological and mechanical behavior of autologous pericardium used for tricuspid valvular replacement in dogs
Authors: Dureau Georges , Kepenekian Georges , Heynen Yves , Paul Jacqueline , Tabib Alain , Clendinnen Guy , Belleville Jean , Eloy Rosy 
Published: December 2004

AbstractThe fate of autologous pericardium when used to replace a tricuspid valve leaflet has been investigated in dogs. Changes have been studied by means of macroscopic, mechanical, histological, scanning electron microscopy, and in vitro culture techniques. In each of nine experiments the valve failed and death occurred within the first 15 post‐operative days. Retraction, thickening of the cusp, fibrinous deposition and/or tissue rupture were associated with a decrease of resistance to traction tests, decrease of elasticity and increase of viscosity of the implanted tissue. The early behavior of autologous pericardium was characterized by precocious inflammatory reaction on the valve leaflets, focal disruption of the collagenous structure of the leaflets, absence of fibroblastic cell infiltration as confirmed by in vitro culture of implanted pericardium and the lack of endothelial‐like cell surface at the 10th–15th postoperative day.
Surface spectroscopic studies of avcothane
Authors: Graham Susan W. , Hercules David M. 
Published: December 2004

AbstractAvcothane is a commercially available copolymer of polyether, polyurethane, and polydimethylsiloxane; it is used primarily in aortic balloon pumps. The pumps consist of three segments which are cemented or fused together to form the balloon. The objective of this work is to characterize the surfaces, inside and outside, of the three balloon pump sections. By using x‐ray photoelectron spectroscopy (ESCA), ion scattering spectroscopy (ISS), and secondary ion mass spectrometry (SIMS) a detailed analysis of the Avcothane surfaces can be performed and comparisons between various surfaces made. Previous workers have reported ESCA and Auger electron spectroscopy (AES) measurements of Avcothane and comparisons with their results will be presented. SIMS and ISS are useful analytical tools for studying polymeric biomaterials because these techniques are usually more surface sensitive than either ESCA or AES. SIMS and ISS data indicate that a thin fluorine‐rich film (probably a fluorocarbon polymer) is present on the Avcothane surface. Signals from the fluorine‐rich layer are more intense from the inside of the balloon pump and the intensity generally decreases from top to bottom. The outside sections of the aortic balloon pump also show the presence of fluorine, but the signals are far less intense than from the inside. One possible explanation for the fluorine‐rich layer is that a fluorine‐containing compound is deposited on the balloon pump during molding and preparation. Another possibility is that the layer is deposited during preparation of the Avcothane itself, but is essentially removed from the outside during sterilization.
Effect of hydrophilic and hydrophobic microdomains on mode of interaction between block polymer and blood platelets
Authors: Okano Teruo , Nishiyama Shoji , Shinohara Isao , Akaike Toshihiro , Sakurai Yasuhisa , Kataoka Kazunori , Tsuruta Teiji 
Published: December 2004

AbstractABA‐type block copolymers composed of 2‐hydroxyethyl methacrylate (HEMA), a hydrophilic monomer, and styrene (St), a hydrophobic monomer, were synthesized by the coupling reaction of telechelic oligomers used as prepolymers. These block copolymers may be represented as microphase‐separated structures. It is therefore possible to change the balance between hydrophilicity and hydrophobicity in the level of an assembled order of macromolecules. In response to the relative composition of the copolymers, three typical morphological patterns were observed in electron microscopic photographs: dispersed domains of continuous St chains in the region of HEMA chains, alternate HEMA and St lamellae and finally, dispersed phases of continuous HEMA chains in the region of St chains. The effect of the hydrophilic and hydrophobic microdomains of the copolymers on the mode of interaction between polymers and platelets was studied by the microsphere column method. In the case of homopolymers and random copolymers, a significant degree of platelet adhesion and aggregation was observed. However, the degree of platelet adhesion and deformation was suppressed on the surfaces of the block copolymers containing 0.608 and 0.347 mole fractions of HEMA whose microdomains were hydrophilic‐hydrophobic lamellae and isolated hydrophilic islands in hydrophobic areas, respectively. These results show that the microphase‐separated structures were antithrombogenic and prevented platelet adhesion and deformation. On the basis of the results obtained, the interaction between platelets and polymer surfaces was described in terms of the effect of hydrophilic and hydrophobic microdomains.
Permanent set and stress relaxation in elastomeric impression materials
Authors: Cook Wayne D. 
Published: December 2004

AbstractThe permanent set of a range of elastomeric impression materials, used in dentistry, was investigated as a function of the materials′ age and the duration and level of the deformation. The permanent set appears to be primarily controlled by the rate of polymerization at the time of deformation. However, stress relaxation experiments revealed that, for condensation silicone and in particular polysulfide elastomers, bond interchange reactions produce additional permanent set. The rate of recovery of the elastomers from deformation was very rapid and was consistent with the influence of entanglements in the network.
Friction and wear properties of polymer, metal, and ceramic prosthetic joint materials evaluated on a multichannel screening device
Authors: McKellop H. , Clarke I. , Markolf K. , Amstutz H. 
Published: December 2004

AbstractA 12‐channel wear screening device was used to compare the wear properties of a variety of prosthetic joint materials. Two types of tests were run: (1) Ultrahigh molecular weight (UHMW) polyethylene bearing against metal or ceramic counterfaces and (2) various polymers bearing against 316 stainless steel as a standard counterface. Wear was quantified by weighing the polymer specimens, with presoaking and control‐soak specimens used to minimize the error due to fluid absorption. The specimens were lubricated with bovine blood serum. Friction and polyethylene wear was very low with each of the metals (316 stainless steel, cobalt‐chrome alloy, multiphase alloy, and titanium 6–4 alloy) such that the differences in wear rate would not be significant in terms of choosing a material for clinical application. However, titanium 6–4 alloy was found to be especially susceptible to abrasive wear by particles of acrylic cement. Nitrided titanium 6–4 counterfaces were impervious to acrylic abrasion. Polyethylene wear against highly polished, fully dense ceramics (Sialon, Alumina, Macor, and pyrolytic graphite) was as low as that with the metal counterfaces. Wear increased slightly with increasing ceramic surface roughness. The coefficient of friction of polyethylene against pyrolytic graphite was two to three times higher than with the metals or other ceramics. All of the alternate polymers underwent more wear than UHMW polyethylene. Teflon and polyester, two polymers that have proven unsuccessful in prior clinical use, had wear rates 1600 and 830 times greater than polyethylene, respectively, an indication that the laboratory wear test provided a quantitative prediction of the behavior of the materials in vivo. However, it was difficult to assess the clinical significance of the less extreme wear rates since the ability of the tissues encapsulating a prosthesis to accomodate wear debris is not known on a quantitative basis.
Development of a silica‐free silicone system for medical applications
Authors: Ashar B. , Ward R. S. , Turcotte L. R. 
Published: December 2004

AbstractFiller‐free silicones are believed to be more blood‐compatible than those containing fillers. An ultrapure silica‐free room temperature vulcanizing silicone system was prepared and characterized using a swelling experiment, an infrared spectrometer, an x‐ray spectrometer, a scanning electron microscope and neutron activation analysis. The polymer was found to be suitable for medical applications needing an extremely smooth surface.
Adsorption of proteins from plasma to a series of hydrophilic‐hydrophobic copolymers. II. Compositional analysis with the prelabeled protein technique
Authors: Horbett Thomas A. 
Published: December 2004

AbstractPlasma protein adsorption is an important initial event in the response of tissue to foreign materials. Little is known about the way in which the chemical properties of materials influence the nature of the adsorbed layer and thus the later cellular responses. In this study, the amounts of fibrinogen, immunoglobulin G, albumin, and hemoglobin adsorbed from plasma to a series of HEMA‐EMA random copolymers varying in hydrophilicity was measured. The adsorption of each protein varied in a characteristic way with copolymer composition probably reflecting a different affinity of the proteins for the various copolymers. A complex variation in the composition of the adsorbed protein layer on polymers varying in hydrophilicity was thus evident. Surface enrichment of the proteins, calculated as the ratio of the surface and bulk fraction of each protein, also varied with copolymer composition, and indicated substantial differences in the composition of the surface and bulk phases. Surface area variations among the copolymers, preferential adsorption of 125I proteins, and the possibility of structural degradation of 125I proteins in plasma were investigated but did not appear to influence the adsorption results. The ability of polymers to fractionate plasma proteins and concentrate them at their surface is concluded to be a key factor in the complex processes which determine the compatibility of polymers in vivo.
Blood compatibility of hydrophilic polymers
Authors: Ikada Y. , Iwata H. , Horii F. , Matsunaga T. , Taniguchi M. , Suzuki M. , Taki W. , Yamagata S. , Yonekawa Y. , Handa H. 
Published: December 2004

AbstractBlood compatibility has been studied for hydrophilic polymers such as poly(vinyl alcohol) (PVA), its derivative, and polyethylene grafted with water‐soluble monomers. The surfaces in contact with electrolyte solutions have been characterized by measuring the zeta potentials. The study of plasma protein adsorption on these polymers has revealed that bovine serum albumin as well as bovine serum fibrinogen adsorbs to a lesser extent as the hydrophilicity of the polymers increases. Platelet deposition and fibrin formation, examined using platelet‐rich plasma, have been found to take place less significantly on PVA as well as sodium acrylate‐ and acrylamide‐grafted polyethylene than on nongrafted and acrylic acid‐grafted polyethylene. Ex vivo experiments with canine whole blood have shown that formation of thrombus on PVA is less than on siliconized glass but increases upon heat treatment which reduces the hydrophilicity. When PVA tubes of about 1 mm diameter are anastomosed to the carotid artery of rat, the patency rate is found to depend strongly on the anastomotic technique. From the results on the zeta potential and the experiments in vitro and ex vivo it can be concluded that the material having a surface from which solvated, neutral chains are extended into the outer aqueous phase may exhibit excellent resistance to thrombus formation.
The effect of carbon fiber reinforcement on contact area, contact pressure, and time‐dependent deformation in polyethylene tibial components
Authors: Wright T. M. , Fukubayashi T. , Burstein A. H. 
Published: December 2004

AbstractTo study the mechanical behavior of a commercially available UHMWPE reinforced with carbon fibers, measurements of contact area, contact pressure and time‐dependent deformation were made on tibial components from a contemporary total knee replacement loaded to physiological levels. For comparison, similar measurements were performed on identical components manufactured from plain UHMWPE. Contact area and pressure results reflected the increased stiffness of the carbon‐UHMWPE material, with smaller contact areas and generally higher contact pressures versus the plain UHMWPE at the same load. Stresses in both materials under the contact area approached or exceeded the yield stresses for the materials when the physiological load was high or the radius of the femoral component indenter decreased (similar to flexion of the knee). Time‐dependent deformation over a 24 h period was reduced significantly in the carbon‐UHMWPE components for a high physiological load.
Investigations on the galvanic corrosion of multialloy total hip prostheses
Authors: Lucas L. C. , Buchanan R. A. , Lemons J. E. 
Published: December 2004

AbstractTotal hip prostheses combining cobalt and titanium alloys in direct physical contact are currently being used. The purpose of this paper was to investigate the possibility of an accelerated corrosion occurring due to the coupling of these alloys. Electrochemical corrosion studies based on mixed potential and protection potential theories were used to study thein vitroeffects of coupling the titanium and cobalt alloys. Verification of these studies was made by direct coupling experiments. Macroscopic examination of surface features of four retrieved total hip prostheses ranging from 0–6 years implantation were conducted. The electrochemical studies predicted coupled corrosion potentials of ‐0.22 V and low coupled corrosion rates of 0.02 μA/cm2. Direct coupling experiments verified these results. Cobalt‐titanium interfaces on the implants were macroscopically examined, and no instances of extensive corrosion were found. Overall, thein vitrocorrosion studies and the examination of retrieved prostheses predicted no exaggeratedin vivocorrosion due to the coupling of these cobalt and titanium alloys.
Determination of partition coefficients of acrylates, methacrylates, and vinyl monomers using high performance liquid chromatography (HPLC)
Authors: Fujisawa Seiichiro , Masuhara Eiichi 
Published: December 2004

AbstractRetention times (Rt) for acrylates, methacrylates, and vinyl monomers were measured with two different columns (C18 Corasil and C8 LiChrosorb) using reverse‐phase HPLC in order to obtain their partition coefficients between 1‐octanol and water (log P). The log P values of test compounds were determined from the regression curves between RT and log P values of a number of standards using C8 LiChrosorb. The log P values obtained in this manner agreed closely with the log P values observed in previous studies. However, the peaks of these compounds were not sharp and some compounds were eluted for more than 10 min. Thus, the measurement of accurate Rt values is tedious. C18 Corasil was therefore used for this experiment in a mobile phase (methanol : water = 85 : 15). The Rt of some methacrylates with P values over 4 were delayed due to the hydrophobic interaction between these compounds and the C18 packing material. However, in the measurable region of the log P values (about −1 to +4), log P correlated linearly with log Rt following two different regression curves: one for aliphatic and aromatic compounds with the functional groups (r = 0.92), and the other for compounds without these groups (r = 0.99). It is concluded that log P values of methacrylates widely used in dentistry can be determined easily and accurately by HPLC.
Anticoagulant activity of a synthetic heparinoid in relation to molecular weight and N‐sulfate content
Authors: Sederel L. C. , van Der Does L. , van Duijl J. F. , Beugeling T. , Bantjes A. 
Published: December 2004

AbstractAddition of chlorosulfonyl isocyanate to CC bonds in cis‐1,4‐polyisoprene and reaction of the adduct with NaOH resulted in the formation of a water‐soluble polyelectrolyte with N‐sulfate and carboxylate groups. The polyelectrolyte showed anticoagulant activity and it was found, just as with heparin, that the activity was related to molecular weight and N‐sulfate content.