bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of bioglass fixation of hip prostheses
Authors: Hench L. L. , Pantano C. G. , Buscemi P. J. , Greenspan D. C.
Published: December 2004

The analysis of the bonding interface between hip prostheses and bone after functional use in animals was carried out. Scanning electron microscopy (SEM) with energy dispersive analysis (EDX), and Auger electron spectroscopy were used to evaluate the bonding interface. Various methods of postsacrifice sample preparation were used to evaluate the effect of such different methods on the analysis of the bonding interface. Comparison of the results with several rat tibia implant experiments is also presented.
Influence of the heat treatment of commercial amalgam alloys on the phase composition of the alloys and the creep of the resulting amalgams
Authors: Vrijhoef M. M. A. , Jensen S. J.
Published: December 2004

The influence of heat treatment of dental alloys at several temperatures on the phases present in the alloy and the creep of the resulting amalgam as well as the correlation between phase changes and the creep was investigated. A dependence of the creep on the temperature of the heat treatment of the alloy was established. Substantial phase changes were observed after the different heat treatments. No correlation was detected between the creep rate and the changes in phases present in the dental alloys. A thermodynamically oriented explanation of the relation between the creep of the amalgam and the state of (non‐) equilibrium of the corresponding amalgam alloy was proposed and discussed.
Studies on dental self‐curing resins. XV. Application of nitrene to reactive adhesive with a tooth
Authors: Nakabayashi Nobuo , Hayata Shigeru , Masuhara Eiichi
Published: December 2004

Effectiveness of p‐azidobenzoyloxyethyl methacrylate on the adhesion of a tooth was studied. This methacrylate, dissolved in suitable monomer solvents such as 2‐hydroxyethyl methacrylate, was painted on ivory‐ or acid‐etched enamel and the surface was irradiated by ultraviolet light. Photolysis of the azide produced a nitrene which was reactive with polypeptides in the tooth. As the treated surface must have affinity with methyl methacrylate (MMA) and poly (methyl methacrylate) (PMMA), it was joined with a PMMA bar by the self‐curing resin. The adhesive strength was 100 kg/cm2 with ivory or 65 kg/cm2 with enamel. Graft copolymerization of methyl methacrylate onto collagen may take place by the nitrene prepared in situ by photolysis of the azide. Subject to satisfactory biologic evaluation, this coupler may be useful in the development of adhesive dental filling materials and fissure sealants.
Biodegradability and tissue reaction of random copolymers of L‐leucine, L‐aspartic acid, and L‐aspartic acid esters
Authors: Marck K. W. , Wildevuur Ch. R. H. , Sederel W. L. , Bantjes A. , Feijen J.
Published: December 2004

A series of copoly(α‐amino acids) with varying percentages of hydrophilic (l‐aspartic acid) and hydrophobic monomers (l‐leucine, β‐methyl‐l‐aspartate, and β‐benzyl‐l‐aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr.

The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction.
Development of semicrystalline poly(vinyl alcohol) hydrogels for biomedical applications
Authors: Peppas Nikolaos A. , Merrill Edward W.
Published: December 2004

Swollen crosslinked poly(vinyl alcohol) (PVA) networks were developed and tested as potential biomaterials. They were prepared by electron‐beam irradiation of aqueous PVA solutions at various temperatures and doses of irradiation. These materials were characterized by low mechanical properties and especially by low elongation at break and ultimate tensile strength. Reinforcement was achieved by a two‐stage dehydration‐annealing process, introducing crystallites in the polymeric network. Improved mechanical properties were achieved due to the presence of this crystalline PVA phase. Due to their structure, these hydrogels are proposed to be used as biomembranes for selective transport of macromolecules and as biomaterials for synthetic articular cartilage applications. Surface heparinization was accomplished by reacting heparin to the hydroxyl groups of the PVA surface, through covalent acetal bridges.
The strength of LTI carbon dental implants
Authors: Shim Hong S.
Published: December 2004

In vitro mechanical tests have been performed on a variety of LTI pyrolytic carbon blade‐type dental implants, and the test results have been analyzed using an analytical model. Tensile stresses at fracture were calculated to be about 5 × 104 psi and 8 × 103 psi in the LTI carbon coating and the graphite substrate, respectively. These values are close to their respective fracture strengths. The fracture loads predicted by the model are in good agreement with data obtained from the mechanical tests and are higher than forces expected in mastication.
Porosity in the base metal removable partial denture casting alloys relative to observable metallographic features
Authors: Lewis Arthur J.
Published: December 2004

A series of tensile test pieces of the dimensions stated in the American Dental Association Specification No. 14 were produced using both nickel‐base and cobalt‐base removable partial denture casting alloys. Normal dental casting techniques were employed. Appropriate sections from each specimen were sectioned to half of their original thicknesses, embedded in heat‐ and pressure‐cured conducting mounts, and polished for metallurgical examination. A double electrolytic etching technique was used, employing serially two solutions, in order to maximize the amount of metallographic detail visible. The method proved particularly valuable in the case of the nickel‐base alloy as it indicated the presence of considerable interdendritic segregation. The incidence of porosity was evaluated throughout all sections of the specimens and, although found to be especially prevalent in those regions where gross shrinkage effects might be expected to occur, it was also shown to have a diffuse intergranular and interdendritic distribution.
Tolerance of mouse macrophages in vitro to barium sulfate used in orthopedic bone cement
Authors: Rae T.
Published: December 2004

Barium sulfate, used as a radio‐opaque marker in some orthopedic bone cements, has been shown to escape into the surrounding tissues. This may present a potential hazard. In particular, phagocytic cells may be exposed to relatively high internal levels of barium once the particles have been phagocytosed.

Mouse peritoneal macrophages exposed to barium sulfate for periods up to 144 hr showed a marked cytoplasmic vacuolization from which they recovered only partially. Barium sulfate did not appear to damage the cell membrane as judged by lactic dehydrogenase release.

In the relatively low doses and with the periods of exposure described here, barium sulfate does not appear to present a serious toxic hazard in the short term. It is possible, however, that longer exposures and larger doses may result in the death of phagocytic cells which have ingested barium sulfate.
Presence of adipose fat as a criterion of implant compatibility
Authors: Kaminski Edward J. , Shenk Michael W. , Oglesby Richard J.
Published: December 2004

An analysis of the tissue sections from previous implant studies was performed to define additional criteria which could be considered in determinations of biocompatibility of implant materials.

Adult albino rabbits were implanted with biomaterials in the sacrospinalis muscle for periods of 2, 6, 18, and 54 weeks. Fourteen different implant materials were used in this study. The tissues were examined histologically for the appearance of adipose fat cells within the membrane surrounding the implant as an important criterion of tissues implant compatibility. The results were compared with other previously used criteria in judging biocompatibility of implant materials. For the most compatible nonreactive materials, adipose tissue formation within the pseudomembrane began at 6 weeks and was quite extensive at 54 weeks. The reactive materials studied by us did not exhibit this phenomenon.
A percutaneous implant using a porous metal surface coating for adhesion to bone and a velour covering for soft tissue attachment: Results of trials in pigs
Authors: Fernie G. R. , Kostuik J. P. , Lobb R. J. , Pilliar R. M. , Wong E. , Binnington A. G.
Published: December 2004

A percutaneous implant for the attachment of an artificial limb has been designed and tested in 14 pigs. Firm fixation to beone was achieved with the porous‐surface layered metal intramedullary stem design in some cases. Dacron velour was used at the soft tissue interface. Evidence of soft tissue ingrowth was seen. However, the velour was unable to maintain adequate epithelial adhesion to form an anatomical seal and a barrier to bacteria.
An approach to the soft tissue/synthetic material interface
Authors: Bagnall Robert David
Published: December 2004

It is argued that chemical modification of soft tissue implants in the hope of obtaining an associated tissue response is unlikely to succeed as a method for studying the fundamentals of implant/tissue interactions. An alternative approach is proposed which places greater emphasis on the interfacial interactions (such as protein adsorption) which occur after implantation, in a manner paralleling current advances in knowledge of the blood/material interface. From simple arguments, it is proposed that the observed similarities in soft tissue response of hydrophobic materials may result from irreversible protein adsorption, and that if unusual tissue responses are possible they are likely to be found only with hydrophilic implants. The possibility of a critical hydrophilic/hydrophobic character which an implant must possess for essentially irreversible protein adsorption is also discussed.
Biocompatibility testing of polymers: In vitro studies with in vivo correlation
Authors: Rice Robert M. , Hegyeli Andrew F. , Gourlay Stuart J. , Wade Clarence W. R. , Dillon James G. , Jaffe Howard , Kulkarni R. K.
Published: December 2004

An in vitro method has been developed for screening of candidate biomaterials in an early phase of their development. The test is based on L‐929 mouse fibroblast cultures and their response to powdered polymer samples. It applies microscopic observation for the detection of morphological changes, uses dye exclusion testing for cell viability determination, and utilizes estimation of population doublings as an end point. The test is shown to be reliable and reproducible and is compared to in vivo implantation studies in rats, previously reported.
Protein sorption on polymer surfaces measured by fluorescence labels
Authors: Brynda E. , Drobník J. , Vacík J. , Kálal J.
Published: December 2004

Fluorescence labeling can be used in studying protein sorption on various surfaces with a sensitivity of about 10−8 g/cm2, commensurate with radioactive labeling. Fluorescamine proved to be the most suitable compound for studying protein sorption on hydrophilic gels, because, unlike fluoresceine isothiocyanate and dansylchloride, free fluorochrome does not interfere with measurements. Sorption properties of labeled serum albumin were tested on poly(2‐hydroxyethyl methacrylate), on the copolymer of 2‐hydroxyethyl methacrylate with methyl methacrylate, and on polyethylene. Labeling does not cause aggregation of the protein, but, as expected, it shifts and somewhat broadens its electrophoretic band while at the same time slightly raising its affinity toward hydrophobic surfaces.
Experimental bladder substitution using a biodegradable graft of natural tissue
Authors: Novick Andrew C. , Straffon Ralph A. , Koshino I. , Banowsky Lynn H. , Levin Howard , Kambic Helen , Nosé Y.
Published: December 2004

A controlled canine experimental study has been performed to test the application of a biodegradeable graft to vesical augmentation. The graft, after providing initial bladder enlargement, is progressively reabsorbed while serving as a foundation for the regeneration and healing of the layers of the bladder remnant. Follow‐up studies at 1 year revealed no urinary infection, calculi, extravasation of urine, or rejection of the material. Normal bladder capacities were maintained throughout the study and the reconstructed bladders functioned normally. The biodegradable graft was equally successful when applied either to a histologically normal bladder remnant, or to a pathological bladder of intramural fibrosis. These results suggest that this material may be well suited to clinical bladder substitution in humans.
Effect of simplex liquid methyl methacrylate monomer on cells
Authors: Welch Ardyce B.
Published: December 2004

The effect of methyl methacrylate monomer used for polymerization of surgical bone cement on phagocytosis, blood cells, tissue cells in culture, and bacteria was investigated. A concentration of 0.5% monomer reduced the ability of macrophages in vitro to phagocytize cultures of Staphylococcus epidermidis effectively. In vivo, 0.03 ml injected into mice also reduced the capacity of peritoneal macrophages to phagocytize bacteria. Extent of cellular damage to blood cells varied with concentration of monomer used and time of contact but, in general, 0.5% was sufficient to alter morphology and viability of blood cells and tissue cells in culture. Polymorphonuclear neutrophils sustained more damage than other types of blood cells. Only minor alterations were detected from cooled, polymerized cement. These studies support the concept that the monomer, as well as mechanical and thermal factors, may be responsible for some of the tissue changes seen at the site of implant of bone cement following total joint arthroplastic surgery.
Surface chemical analysis of avcothane and biomer by Fourier transform IR internal reflection spectroscopy
Authors: Sung C. S. Paik , Hu C. B. , Merrill E. W. , Salzman E. W.
Published: December 2004

During the solvent casting process, one side of the polymer film is exposed to air while the other side is in contact with a substrate, used as a mold. We have studied the effect of this difference in exposure during casting on the chemical composition of two types of segmented polyurethane,5 Biomer

Biomert™, Ethicon Corp., Somerville, N.J.

and Avcothane,

Avcothanetm™, Avco‐Everett Co., Everett, Mass.

by using Fourier transform IR internal reflection spectroscopy. Also, a depth‐composition profile was obtained by placing a thin barrier film between the reflection plate and the polymer film.

In Avcothane, the air side, which is the blood‐contact side, contains a greater amount of the soft segment than the substrate side, and this is more pronounced in the layer closer to the surface. The anisotropy in composition is more drastic when the silicone content is compared. In a layer about 1.5 μ thick, one can detect a greater amount of silicone in the substrate side than in the air side. However, when one averages the concentration in a layer of about 0.8 μ, the trend is reversed; i.e., the greater amount of silicone is now present in the air side than in the substrate side. In Biomer films, the anisotropy in chemical composition is less pronounced. Only a modest increase in the relative content of the soft segment/hard segment is observed in the air side when a depth‐composition profile is obtained.
Adhesion of synthetic organic polymer to soft tissue. III. Effect of some monofunctional compounds
Authors: Wang P. Y. , Llewellyn‐Thomas E.
Published: December 2004

Previous work in this series has shown that some aromatic and n‐alkyl isocynates can significantly improve the adhesion of a fast‐setting polyurethane prepolymer to internal tissue. In the present study, several acyl or aroyl anhydrides, chlorides, and a triaryl chloroalkane have been found to effect various degrees of improvement in the adhesion of fast‐setting prepolymer to tissue. To determine the influence of minor structural changes on adhesion, the isomers of methyl phenyl isocynate and chlorobenzoyl chloride were investigated. The isomers were found to give the same extent of improvement in adhesion of the prepolymer as the parent compound without the methyl or chloro substituents. Among all the reactive monofunctional compounds studied, benzoyl chloride and its chlorobenzoyl derivatives are the most effective. When primed on tissue or admixed as little as a 3% additive in some polymer preparations, these aroyl chlorides can promote the adhesion of many ordinary adhesives to internal tissue. The effectiveness is attributed to the modification of hydrophilic tissue surface by the hydrophobic benzoyl group attached to tissue after reaction. The prosthetic benzoyl group makes the tissue/polymer interface more compatible and the compatibility results in good adhesion.
Antibiotics in acrylic bone cement. In vivo studies
Authors: Welch A. B.
Published: December 2004

In vivo experiments were performed to study elution rates of antibiotics combined with Surgical implex bone cement and efficacy in controlling bacterial infections. Cylinders of bone cement were implanted in animals and at the same time the surgical areas were infected with large numbers of bacteria. Gentamicin and Keflin were eluted from the cylinders in sufficient quantities to completely eliminate or markedly reduce the number of bacteria recovered from infected areas. Animals were also treated with an anti‐inflammatory drug, hydrocortisone, prior to implantation of cylinders and infection. The antibiotics in the bone cement effectively destroyed the bacteria in these animals with impaired inflammatory responses as compared with control animals.
Corrosion behavior of structural phases in high copper dental amalgam
Authors: Marek M. , Okabe T.
Published: December 2004

The effects of crevice corrosion on the major structural phases of a high copper dental amalgam were studied in vitro. Three kinds of samples were used: (1) amalgam prepared from a high copper, single composition alloy, (2) annealed ingots of the Ag3Sn and Cu3Sn phases, and (3) high copper, single composition alloy tablets electroplated with mercury. Specimens were examined in a scanning electron microscope before and after the exposures to a corrosion environment.

The Ag3Sn and Cu3Sn phases were least affected by corrosion. The Ag‐Hg‐Sn phase (γ1) slowly deteriorated, but the attack was nonuniform. The Cu6Sn5 phase exhibited good corrosion resistance, better than that of the γ1 phase. Particles of a tin rich phase of uncertain origin were observed on some of the samples after long exposures.
A study of the normal range of strain, strain rate, and stiffness of tendon
Authors: Herrick W. C. , Kingsbury H. B. , Lou D. Y. S.
Published: December 2004

This paper describes the result of an investigation of strains and strain rates which normally occur in the tendons of the equine foreleg and presents stress‐strain curves and moduli for the tendons at these rates.

It has previously been demonstrated that resistance to flexion of the joints of the distal part of the equine foreleg is provided by a passive system of tendons and ligaments. It is therefore possible, using a large displacement, high‐rate testing machine, to duplicate in the laboratory the strain rates and forces which are normally produced in the tendons of the foreleg of the running horse.

To carry out tendon tests, legs were mounted in the test machine. The superficial flexor tendon was exposed and fitted with an extensometer and a buckle‐type force transducer. Stress‐strain curves were obtained for 13 tendons.

It is shown that strains to 12% and strain rates to 200%/sec occur normally in the superficial flexor tendon. Stress strain curves and tangent modulus are presented for strains from 0 to 10% at rates from 5 to 100%/sec. Tendon modulus is found to be essentially rate independent in this range.
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

The 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

In 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

The 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

The 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

In 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

The 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

The 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

The 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

Current 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

The 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

Plasma 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

Bar‐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

13C 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

In 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

A 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

The 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

A 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

One 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

Amalgams 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

A 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.
Midroelectrode studies of stress‐generated potentials in four‐point bending of bone
Authors: Starkebaum W. , Pollack S. R. , Korostoff E.
Published: December 2004

A microelectrode technique has been developed to enable the study of stress‐generated potentials (SGP) in bone to a spatial resolution of 5 μm. The technique has been used to measure the electrical potentials as a function of bone micromorphology in four‐point bending. Electric fields ranging from 30 to 103 times greater than is measured by conventional macroscopic methods have been discovered at the Haversian canals for human and bovine cortical bone. The amplitude and direction of the electric field in the osteons depend specifically upon the amplitude and the sign (i.e., compression or tension) of the stress. The implications of this finding with regard to the origin of SGP and their possible physiological significance are considered.
Microelectrode study of stress‐generated potentials obtained from uniform and nonuniform compression of human bone
Authors: Iannacone W. , Korostoff E. , Pollack S. R.
Published: December 2004

By use of a previously developed microelectrode technique, the effect of nonuniform stresses on the stress‐generated potentials (SGP) in bone were studied to a resolution of 5 μm. Comparison was made between uniformly and nonuniformly applied compression of human cortical bone. It was found that the radial electric fields for osteons in a specimen under uniform compression were equivalent, and such specimens possessed no macroscopic SGP; for nonuniform compression, the electric fields of osteons differed, and a macroscopic SGP was measured. The magnitude of the macroscopic SGP thus appears to be dependent upon local stress differences and, hence, on the SGP of local regions.
Degradation resistance of some candidate composite biomaterials
Authors: McKenna G. B. , Bradley G. W. , Dunn H. K. , Statton W. O.
Published: December 2004

The degradation resistance of matrix, fiber and composite systems which we have been studying as candidate orthopedic materials has been examined in two appropriate environments. Both resistance to steam sterilization in an autoclave environment and resistance to a simulated physiologic solution have been studied. In the autoclave study, samples were placed in a pressure cooker at 123°C for differing amounts of time and tested for retention of mechanical properties. Results indicate that most of the materials tested could be autoclaved several times, as along as autoclave times did not exceed 1 hr. Longer autoclave times result in an accelerated degradation and loss of strength of all materials except the polypropylene. Polysulfone degrades after even the shortest autoclave duration. Resistance to the simulated physiologic environment was tested by measuring retention of mechanical properties after immersion times in pseudo‐extracellular fluid (PECF) at 37°C for as long as three years. None of the materials showed any significant changes in properties after immersion in the PECF.
Bone ingrowth and stress shielding with a porous surface coated fracture fixation plate
Authors: Pilliar R. M. , Cameron H. U. , Binnington A. G. , Szivek J. , Macnab I.
Published: December 2004

The extent of bone remodelling under metal fixation plates attached to bone by (i) normal screw fixation and (ii) bone ingrowth into a porous metallic surface underlayer sintered to the metal plate was investigated. Extensive bone remodelling was observed under the integrally bonded porous surface layered plate. This remodelling could be attributed to the more extensive stress transfer from bone to metal plate because of the good bone‐to‐implant bonding. The importance of stress shielding with high stiffness implants is demonstrated.