bluuebunny/crossref_metadata_2025_split huggingface dataset:
The redistribution of mercury as observed in the phase transformations in amalgams
Authors: Reynolds C. L. 
Published: December 2004

AbstractAn investigation has been conducted to observe the effect of heat treatment on mercury loss and structural transitions in clinically used amalgams, as well as the individual phases composing dental amalgam. Pure Ag2Hg3 readily loses mercury and transforms to the β1 phase while the remaining amalgams are somewhat more stable. Since essentially no weight loss is observed in clinically used alloys, the mercury, liberated by the γ1 decomposition, reacts with excess Ag3Sn to form a self‐perpetuating reaction, explaining the increases in the β1 and γ2 phases in the Ag3Sn and “True Dentalloy” amalgams. That is, the mercury has redistributed itself within the amalgam.
Studies related to the fracture of partial dentures—fractography of cobalt‐chromium alloys
Authors: Bates J. F. , Scott J. 
Published: December 2004

AbstractThe fracture surfaces of specimens of a cobalt‐chromium alloy fractured in a conventional testing machine have been compared with similar specimens fractured by fatigue. Notched bar impact tests were also carried out and the surfaces of the specimens compared to those fractured in tension and by fatigue. Results show a brittle failure in all cases, although some change in the rate of crack propagation was evident in the fatigue specimens. Clinical evidence suggests that failure of partial dentures is due to bad castings, but some evidence is produced to show that fatigue cannot be eliminated as a cause of failure.
Some observations on the dielectric properties of cardiovascular implant materials
Authors: Milligan Herbert L. , Cleminshaw William T. , William Edmark K. 
Published: December 2004

AbstractBioelectric charge transfer between blood and the vascular wall appears to play a significant role in maintaining vascular homeostasis. Since the surface charge characteristics of the vessel wall are a function of the dielectric properties of the material, a study was made of the dielectric characteristics of various ion permeable materials and their relationship to electrokinetic phenomena and thrombogenicity. The dielectric properties of the ion permeable materials and of animal tissue were determined and found to be strikingly similar. Several models of electrodiffusion phenomena are reviewed with respect to dielectric properties. The electro‐osmotic characteristics of animal tissue and ion permeable materials were investigated, and it was found that animal tissue exhibited electro‐osmotic characteristics to a greater degree than did any other man‐made materials. The propensity of a material to electro‐osmose could not be predicted from the dielectric properties. In addition, no correlation could be found between thrombogenicity and dielectric properties. Dielectric relaxation phenomena is reviewed, and its possible contribution to nonthrombogenicity through the generation of a uniform, constant wall surface charge is presented. It is concluded that to mimic the ion content and mobility characteristics of animal tissue, as determined by dielectric properties, is insufficient to preclude thrombus formation.
An electrical resistance study of the precipitation reaction in a gold‐platinum‐iron alloy
Authors: Sims Julius R. , Blumenthal Robert N. , O'Brien William J. 
Published: December 2004

AbstractThe aging reaction of a 90 wt‐% gold, 10 wt‐% platinum alloy with nominal iron concentrations of 0.04, 0.08, and 0.16 wt‐% iron has been studied using electrical resistance measurements. The electrical resistance was measured as a function of temperature from 300 to 750°C. A decrease in electrical resistance was observed occurring at 350 to 450°C, when heating the solution treated and water quenched specimens containing iron. Subsequent heating and cooling curves follow the gold‐platinum standard. Isothermal electrical resistance measurements were made as a function of time. The data from the specimen containing a nominal iron concentration of 0.16 wt‐% iron was analyzed using the Johnson‐Mehl equation. The shape parameter n was found to vary as a function of aging temperature from n = 0.6 to n = 1. These results have been rationalized in terms of a model involving precipitation of FePt3 at dislocations (400°C) and FePt3 in the shape of a rod at 500°C.
Water and hydrogels
Authors: Jhon Mu Shik , Andrade J. D. 
Published: December 2004

AbstractThe apparent biocompatibility of many synthetic and natural aqueous gel materials has encouraged their study and testing for a wide variety of biomedical device applications. Many of the physical and in particular the interfacial properties of such gels are highly dependent on the organization of water within and on the surface of the hydrogel. Water is an important component of such gels, varying from about 30 to nearly 100 wt‐%, yet the role of water in the gels has been virtually ignored. This paper briefly reviews the nature of water structure in pure bulk water, in solutions, and at interfaces. Polywater or anomalous water is also briefly reviewed. Evidence is presented that the water in many hydrogel systems can exist in at least three different, structurally distinct forms. A hypothesis is presented which can be used to evaluate and study the nature of water in bulk hydrogels. Consideration is also given to the role of organized water at the hydrogel surface on the interfacial properties of such systems.
The in vivo and in vitro corrosion products of dental amalgams
Authors: Otani Hiroshi , Jesser William A. , Wilsdorf Heinz G. F. 
Published: December 2004

AbstractThe purpose of this investigation is to clarify the role of the component phases of dental amalgam in a corrosive environment and to analyze the corrosion products at various stages of formation predominantly by means of x‐ray diffraction methods and energy dispersive x‐ray spectroscopy. The study encompassed in vivo as well as in vitro experiments.Sn, which came from only the γ2 phase, was found to be the sole or main constituent that contributes to the formation of the corrosion products. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SnO} \cdot {\textstyle{1 \over 2}}{\rm H}_2 {\rm O} $\end{document} constituted the majority of the corrosion products formed in the early stages. SnO appeared in corrosion products more than 14 days old.
Adhesion of synthetic organic polymer on soft tissue. I. A fast setting polyurethane adhesive
Authors: Llewellyn‐Thomas E. , Wang P. Y. , Cannon J. S. 
Published: December 2004

AbstractConventional polyurethane prepolymers have been shown to adhere to living biological tissues. However, their setting is not sufficiently expedient to permit convenient applications in vivo. A prepolymer prepared from the highly reactive 6‐chloro‐2,4,5‐trifluoro‐1,3‐phenylene diisocyanate, castor oil, and a trace of pyridine has afforded an adhesive which sets in about 2 min in vivo. The fast setting has resulted in poor adhesion on biological tissue. The bonding has been improved by the inclusion of tolylene diisocyanate in the composition without affecting the fast curing rate of the prepolymer. The dispersion of the adhesive and its cohesion after solidification have been adjusted by other minor additives. Preliminary evaluation on animals indicates that this adhesive is most useful as a hemostatic coating in hepatic lacerations.
Diffusion of anti‐tumor drugs through membranes from hydrophilic methacrylate gels
Authors: Drobník J. , Špaček P. , Wichterle O. 
Published: December 2004

AbstractPermeation parameters of four anti‐tumor drugs across membranes prepared from hydrophilic methacrylate gels were measured and compared with the permeation of NaCl. It was found that by increasing the ratio of butyl methacrylate (BMA) to hydroxyethyl methacrylate (HEMA), the rate of diffusion can be lowered to practically zero at 20% BMA. However, this decrease is different with various drugs due to the interaction of the drug with the gel. Differences by a factor of two were found in our set of drugs. Therefore, each new drug should be tested in this way. In addition a routine testing of dialysing devices by an NaCl solution is suggested as a method for detecting technological imperfections and calibrating the deviations from standard parameters. A chemical modification of the membrane is recommended as the best way for controlling the permeation rate.
Aeration of medical plastics
Authors: Tock Richard M. , Chen Yang Chin 
Published: December 2004

AbstractBecause the metabolic reaction that gives ethylene oxide its sterilizing qualities also takes place with human protein, it is imperative that any residual gas be removed before the sterilized material is used on the patient. This paper presents a method of estimating aeration time required following sterilization of polyvinyl chloride (PVC) to reduce toxic residues to a desired level. The method proposed involves calculation of the coefficient of diffusivity, and the use of a simplified diffusion equation to estimate aeration time.
Adhesion of red cells to foreign surfaces in the presence of flow
Authors: Mohandas N. , Hochmuth R. M. , Spaeth E. E. 
Published: December 2004

AbstractA controlled surface shear stress produced by laminar flow in a rotating disk or parallel plate flow system has been used to study red cell adhesion to glass, siliconized glass, polythylene and Teflon. The results indicate that the shear stress at the surface must exceed a minimum critical value before cells will detach, and that this minimum critical shear stress increases as the time of cellsurface contact is increased. The results also indicate that the minimum critical shear stress for detachment from clean surfaces correlates with the critical surface tension of the material for the four materials studied. Studies with proteincoated surfaces indicate that albumin causes a moderate reduction in the strength of adhesion. The magnitude of the effect was found to be influenced significantly by the substratum material.
A combined metallurgical and histological study of tissue‐prosthesis interactions in orthopedic patients
Authors: Williams D. F. , Meachim G. 
Published: December 2004

AbstractMetallurgical and histological examinations of implants and adjacent tissue removed from orthopedic patients have been performed in a series of 190 cases. The results have been correlated with clinical findings where possible. The two major factors to emerge from this study were that many stainless steel implants corrode in the body and that titanium implants release titanium into the local tissue, which may become discolored.Severe cases of corrosion in stainless steel implants were attributed to faulty manufacturing technique and poor implant usage. This corrosion was frequently associated with crystal‐like “microplates” in the tissue and lead to clinically significant effects in some cases. Less severe cases of corrosion were almost invariably associated with interfaces between components. Susceptibility to this corrosion may be minimised by improvements in design and materials specification.Titanium levels in excess of 2,000 ppm were found in the tissue in 3 cases out of 19 analysed, no specimen of a control series showing greater than 100 ppm. Histological sections showed accumulations of intracellular particles of exogenous origin. The evidence that such titanium release and particle accumulation causes clinically significant effects is only minimal but it is possible that systemic distribution of titanium and remote hypersensitivity effects could arise.
Tissue reaction to metallic wear and corrosion products in human patients
Authors: Winter George D. 
Published: December 2004

AbstractTissues from around surgical implants have been examined by optical microscopy and electron microscopy and by electron diffraction and x‐ray spectrographic techniques. The presence of small alloy fragments and carbides worn from cobalt‐chromium total joint replacements was confirmed. These foreign bodies had been phagocytosed by macrophages and there were no indications that the tissues were damaged by their presence. In 13 of 44 specimens there were granulomatous foci related apparently to the presence of numerous minute particles of unknown composition which had elicited vigorous macrophage reactions.In tissues near stainless steel joints too there were particles of the naked alloy taken up by macrophages and again the fibrous tissue appeared unaffected.Typically the tissues near to stainless steel implants are affected by cytosiderosis. It is deduced that the iron released by corrosion from stainless steel is processed by macrophages locally and there is formed a mixture of hydrated ferric oxides similar to hemosiderin. This may be looked upon as a detoxication mechanism. There is evidence that in some specimens the limit of tissue tolerance for stored iron has been exceeded locally with consequent pathological changes.Another common deposit around stainless steel implants occurs in large plaques. It attracts giant cells and there is evidence that it is fibrotic and cytotoxic.
Transcutaneous implants: Reactions of the skin‐implant interface
Authors: Winter George D. 
Published: December 2004

AbstractOne method of providing an artificial limb for an amputee might be to attach the external prosthesis directly to the skeleton but a major problem is the behavior of the tissues at the point where the prosthesis penetrates the skin surface. Preliminary experiments have been carried out using small flexible implants in porcine skin to study the principles involved. It is confirmed that the epidermis grows down into the dermis around the nonporous materials and the implant‐skin junction is unstable and readily becomes infected. It was found that polytetrafluorethylene with pores of 10 μm diameter and hydron sponge with pores of 40 μm diameter became invaded by fibrous tissue and this appeared to prevent the migration of epidermis alongside the implants and a stable ring of epidermal tissue was formed near the skin surface. A review of other situations where epidermal migration is taking place suggests that epidermis is able to migrate through damaged collagenous tissue, possibly with the help of leucocytic enzymes, but that epidermal cell movement is halted when the epidermal sheet is confronted by heathly collagen bundles.
The role of porous polymeric materials in prosthesis attachment
Authors: Sauer Barry W. , Weinstein Allan M. , Klawitter Jerome J. , Hulbert Samuel F. , Leonard Ralph B. , Bagwell Joseph G. 
Published: December 2004

AbstractPolymeric materials are becoming increasingly popular as prosthetic materials in orthopedic surgery. One of these materials, polyethylene, is capable of being fabricated in a porous form suitable for tissue ingrowth. Porous polyethylene appears to be well suited for prosthesis attachment when bonded to its solid form of other prosthetic materials. Extensive bone growth into porous cylindrical specimens implanted in the canine femur has occurred as early as four weeks. Ingrown tissues appear normal and there is minimal inflammatory response. Mechanical strength of the porous material, though not as great as that of the solid material, does appear to be sufficient for certain orthopedic applications. Current research is directed toward determining interfacial strengths and the mechanical properties of the porous polyethylene‐bone composite.
Study of early sheath development using static nongliding implants
Authors: Hunter James M. , Steindel Carl , Salisbury Roger , Hughes David 
Published: December 2004

AbstractClinical studies will permit only small sections of tendon sheaths to be removed for biopsy at restricted levels as the sheaths were to be used for tendon grafting. In active gliding programs, biopsy has been limited to small sheath sections in immediate relation to the distal or proximal anastomosis where gliding motion may be induced or minimal. In the passive gliding programs, biopsy has been limited to the most proximal segments where considerable folding of the sheath occurs or cul‐de‐sac buckling of the implant may produce irritation.As these were the only practical clinical sources of sheath sections for biopsy and study, the authors felt that a comparison study of sheath development in animals would broaden our understanding in humans. With this objective in mind, three canine laboratory studies were carried out where, for pure purposes of investigation, entire sheath sections were removed at designated time intervals for study.The flexible implants were well accepted, affording the opportunity to observe development of early sheaths in a controlled connective tissue environment, free from the stress of joint motion.The semi‐rigid implants showed equal acceptance in side‐by‐side tissue level of the same dog as the flexible implant. This influenced changes in artificial tendon development from extrusion to the more exacting mold fabrication. It seemed evident that the degree of increase in stiffness of the new artificial tendons to gain a superior surface for gliding and increased strength would not change tissue acceptance providing flexibility was maintained.The cellular response in this study did not seem to represent a foreign body phenomena but an orderly acceptance of the soft tissue environment to the smooth surface of the inert implant.It is concluded that this study confirmed in animals the clinical findings of Mayer, Bunnell, Milgram, and Carroll.The consistent orderly development of the new sheaths formed in response to the static implants is impressive. The authors believe the appearance of these histologic sections are likely correlations with the development of new sheaths around the Hunter Tendon Prosthesis during the three–four week postoperative period when the hand is resting in a functional dressing.
Sheath formation in response to limited active gliding implants (animals)
Authors: Hunter James M. , Subin David , Minkow Frederick , Konikoff John 
Published: December 2004

AbstractExperiments were conducted to further the understanding of tendon reconstructive surgery.A series of 20 dogs was used for replacement of the forepaw extensor carpi radialis tendon (a single tendon only is present in the dog) with active gliding tendon implants. The implants were attached distally and proximally so that new tendon prosthetic designs could be studied as well as new sheath development under gliding conditions.The results, recorded in this paper, show that a “gliding implant” can convert a nonspecific bed of connective tissue or scar into a specific living envelope comparable to a tendon sheath system. This system has been shown to be capable of lubricating and supporting a gliding artificial implant while augmenting normal tendon function. Degrees of active and passive gliding can take place for indefinite periods, providing the mechanical and dynamic capabilities of the new system are understood and controlled. The mature sheath will show a predictable physiologic response to unfavorable stimuli.Further evidence that the new gliding system functions as a physiologic sheath is borne out by the fact that the implant can be replaced in Stage II by a long free tendon graft. The graft is apparently supported in part by fluid nutrition and filmy adhesions between the distal and proximal anastomosis.
Physical characteristics of setting of acrylic bone cements
Authors: Lautenschlager E. P. , Moore B. K. , Schoenfeld C. M. 
Published: December 2004

AbstractAn investigation was conducted to determine the general physical characteristics of self‐curing acrylic resin systems in terms of their potential utilization in total hip arthroplasty.Exothermic temperature, working and setting times were monitored with thermocouples placed in acrylic masses insulated via a Teflon mold. Mechanical strengths were run in an Instron testing machine. The same trends were noted in all systems studied.As thickness or mass increased, the maximum temperature and the setting time increased. As the powder to liquid ratio increased (thereby relatively less liquid), the maximum temperature, set times and dough times decreased, while the working time was essentially unaffected. As the ambient temperature decreased, the maximum temperature decreased while the dough, working and setting times increased.The mechanical strengths of the systems cured at one atmosphere are low compared to high temperature and pressure curing. Flowability of the materials decreases quickly as final set time is approached.Although trends are similar in many self‐curing acylic systems minors shifts in complex proprietary compositions can produce a wide span or working and setting times. Because the surgical team controls such parameters as the mass employed, the amount of liquid introduced, and the ambient temperature it is important that they continuously re‐evaluate their handling procedures particularly if new acrylic cements would be introduced.
The potential for poly‐α‐amino acids as biomaterials
Authors: Anderson J. M. , Gibbons D. F. , Martin R. L. , Hiltner A. , Woods R. 
Published: December 2004

AbstractPoly‐α‐amino acids have been investigated for possible use in a wide variety of biomedical applications. These range from dialysis membranes to artificial skin substitutes to degradable sutures. The large number of available α‐amino acids potentially provides an extremely large number of poly‐α‐amino acids. The majority of materials investigated to date are copolymers composed of two components, one of which usually provides the desired property for the given application.This paper deals with the further examination of a series of γ‐benzyl‐L‐glutamate‐L‐leucine copolymers. Evidence is provided on the effect of these copolymers on the biological environment as determined by implantation in rats up to 200 days. In vitro tests were also performed and the effect of these tests on the stress‐strain properties of one of the copolymers is presented.Preliminary evidence on biodegradable copolymer films is also included. These materials have free γ‐carboxyl groups on the glutamate components.
Pyrolytic biocarbon materials
Authors: Olcott Eugene L. 
Published: December 2004

AbstractCarbon is one of the most attractive biomaterials in many respects. Recent developments in high strength carbon materials for the aerospace industry have led to new forms of carbon which have good structural properties. Several of these, based on a vapor‐de‐posited pyrolytic graphite matrix, are described. A needle‐like silicon‐carbide strengthened pyrolytic graphite has been implanted in rabbits and chimpanzees with encouraging results. Applications are being sought.
Multiphase MP35N alloy for medical implants
Authors: Younkin C. N. 
Published: December 2004

AbstractThe biomaterials engineer of today has an extremely limited choice of approved metallic implant alloys with which to conduct his studies. There is essentially no incentive for larger companies to initiate basic research in the biomaterials field. New alloys which would have the best chance of developing as biomaterials would be “spin‐off” alloys from somewhat related industries and currently in production. MP35N is just such a spin‐off alloy with a background of years of in‐vitro testing and use in corrosive environments. When compared to the desired implant material requirements, the material properties required of MP35N for present applications readily indicate its potential use as a biomaterial.It is a castable alloy which exhibits good as‐cast ductility. In the wrought condition, yield strength levels from 60,000 to over 310,000 psi are possible with accompanying good ductility characteristics. Excellent stress corrosion cracking resistance and improved fatigue strength over present cast implant material are also characteristic of MP35N. Results, to date, from in‐vivo tests indicate tissue compatibility of MP35N at least comparable to HS‐21 (Vitallium).Possible medical applications for MP35N would include hip and knee joints, bone plates, heart pacer electrodes, suture wire and clips, and Endosseous blade implants.