bluuebunny/crossref_metadata_2025_split huggingface dataset:
The elastic constants of the constituent phases of dental amalgam
Authors: Grenoble Dale E. , Katz J. Lawrence 
Published: December 2004

AbstractThe pressure variations of the elastic constants of the constituent phases of dental amalgam (γ–Ag3Sn, γ1–Ag2Hg3, and γ2–HgSn7–8) were investigated in the 0–50 kilobar range. The velocities of propagation of longitudinal and transverse ultrasonic waves were measured using an ultrasonic interferometer and a solid media pressure apparatus. Computer analysis yields the pressure dependence of the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio; atmospheric pressure values are obtained by back extrapolation from the high pressure measurements. The values of these elastic constants are related to the crystallographic structures of the individual alloys. The possibility of high pressure first order polymorphic transitions in γ and γ2 is also discussed.
Elemental carbon as a biomaterial
Authors: Benson Jim 
Published: December 2004

AbstractAdvanced forms of elemental carbon were identified as potential implantable prosthetic materials and a study was conducted to determine specific applications. A survey of the carbon industry established material sources and specifications on available types of material. Specimen materials were supplied to several research organizations for in‐vivo evaluation and produced acceptable results. Specific designs have been generated for a broad range of implantable prosthetics and prototypes have been provided for preliminary evaluation. The feasibilty of an organic mechanical attachment between cortical bone tissues and elemental carbon has been successfully demonstrated.
Porous titanium surgical implant materials
Authors: Hirschhorn Joel S. , McBeath Andrew A. , Dustoor Manek R. 
Published: December 2004

AbstractPorous pure titanium and titanium‐6% aluminum‐4% vanadium alloy materials, made by several powder metallurgy techniques, have been studied for potential use as surgical implant materials. Tissue ingrowth into open porosity and favorable physical properties have been found. Tensile strength and ductility data are presented as a function of density. Microscopic observations include scanning electron microscope pictures of the surface of specimens prior to implantation in animals, photomicrographs of the internal pore structure, macrophotographs of surfaces before and after polishing, and histological photomicrographs illustrating the nature of the tissue ingrowth found.
Skeletal extension of limb prosthetic attachments–problems in tissue reaction
Authors: Mooney Vert , Predecki Paul K. , Renning James , Gray James 
Published: December 2004

AbstractThe skeletal attachment of a limb prosthesis approaches two specific and separate problems in tissue reaction to prosthetic materials: Skeletal fixation and trancutaneous interface.The skeletal fixation problem must be looked upon as a method to distribute the stress concentration of prosthetic material in such a manner so that living tissue is not embarrassed by prolonged excessive pressures. One must consider the functional mechanical stresses separate from the toxicological reaction of living tissues to prosthetic materials. Our current experience identifies the fact that vitreous carbon is extremely benign from the standpoint of living tissue reaction. Moreover, when placed in the configuration of irregular surfaces, it apparently encourages bone growth contiguous with the material. To this point, however, the reaction of living material to broad surfaces contiguous with vitreous carbon has not placed under concentration of functional stresses. Porous ceramic to this date has not supplied an appropriate answer to this problem.Transcutaneous perforation is available in the clinical sense only when a method can be presented which requires no specific hygiene and dressing. No drainage at all must be the rule at a transcutaneous perforation. Vitreous carbon in our experience so far has made contiguous epithealization feasible down the neck of a skin perforation. Four millimeters, from our experience, seems to be an appropriate location of epithelial downgrowth before transition into non epithealized connective tissue is available. The use of fixation skirts is felt to be necessary to provide stable, transcutaneous perforation.This paper presents evidence of the favorable tissue reaction both from a skeletal and cutaneous standpoint to vitreous carbon materials. A specific design for the successful skeletal fixation limb prosthesis is as yet not currently available and must await further clinical experience with human skin reaction to transcutaneous devices.
Ceramics in surgery
Authors: Welsh R. P. , Macnab Ian 
Published: December 2004

AbstractA study has been made of the ceramic‐epoxy composite “Cerosium.” Experiments were conducted to evaluate the tissue reaction to such material and the extent of bonding established between ceramic and the tissues in which it was implanted. It was found that this material was well tolerated by the body and obtained definite fixation within the tissues when implanted into both bone and tendon. This occurred, however, not by the active infiltration of tissue but by fibrous encapsulation and it is recommended that for more meaningful stabilization, material of larger pore size is required.When Cerosium was implanted into the knee joints of rabbits, it was found to be unsuitable for intra‐articular use because of the abrasive effect on the opposing cartilage and bone surfaces and the susceptibility of the material itself to abrasive wear. Furthermore, a full mechanical evaluation of standard specimens of Cerosium showed it to be degraded within the body due to a breakdown of the impregnating polymer.Ceramic‐epoxy composites require a strong matrix and a totally stable impregnating material. While mechanically suited to replacing weight bearing surfaces, a smooth surface glaze is essential to avoid abrasive effects upon the opposing bone surface. Further investigation is required before these materials can be fully accepted into the armamentarium of the implant surgeon.
Problems related to the maintenance of chronic percutaneous electronic leads
Authors: Miller Jo , Brooks C. Emerson 
Published: December 2004

AbstractThe maintenance of percutaneous cables for physiological monitoring or for the introduction of power to artificial organs is an attractive concept, but two problems interfere with their long‐term survival. The exit sites regularly become infected, and the preparation is subject to disruption by the animal.These two problems can be solved by the design of a suitable skin outlet fixture of Teflon and velour fabric. The skin margins proliferate and adhere to the velour, producing a dry bacteria‐proof seal which prevents the development of infection. The skin outlet fixture is shaped so that it is immobilized in relation to the surrounding skin, preventing excessive strain from being applied to the fabric‐skin interface.Skin outlet fixtures of porous ceramic offer theoretical advantages, but there has been little success in attempts to induce the skin margins to proliferate into the porosities of the ceramic.
Development of ceramic and ceramic composite devices for maxillofacial applications
Authors: Driskell T. D. , O'Hara M. J. , Sheets H. D. , Greene G. W. , Natiella J. R. , Armitage J. 
Published: December 2004

AbstractCeramic and ceramic composite materials and devices were developed for specific maxillofacial applications. These applications included: (1) Replacement of hard tissue voids in low stress areas with a phosphate‐bonded alumina‐foamed ceramic and a calcium aluminate‐bonded alumina foam; (2) development of porous ceramic‐coated metallic devices for stabilization of mandibles with avulsed segments; (3) development of implantable ceramic tooth roots onto which more or less conventional crowns may be mounted.Efforts to date have been rewarding. Using the rhesus monkey for all experimental implant work, incorporation of porous ceramic foam prostheses to eliminate maxillary defects has been accomplished. Also, we have succeeded in stabilizing the mandible where segments of from 3 to 8 mm were removed. Bridging of the gap with new bone occurred within 6 weeks resulting in a total regeneration of the resected area with restoration of normal mandibular function. Finally, implantable tooth roots were developed. Three different surface treatment techniques have been used on a basic high‐density alumina core. The first is a high‐density matt finish which can only permit a fibrous tissue attachment or bony approximation but no ingrowth. The second is a porous alumina coating intended to permit bone ingrowth. The third is a rough surface consisting of particles of alumina sintered to the surface to maximize the bone/ceramic interface shear strength potential. Implantations of both anterior and posterior tooth roots with all three surface configurations have been successful for periods of up to six months.
Ceramic metal composites for surgical implants
Authors: Cook William E. , Manning Charles R. , Hurt John C. , Taylor Duane F. 
Published: December 2004

AbstractThe mechanical properties of a series of ceramic‐metal composites have been evaluated to determine their potential as implant materials. Hot pressing procedures were developed for the preparation of wire reinforced, calcium‐aluminate matrix composites. Hot pressed composites containing 5% tungsten fiber were found to exhibit flexural strength equivalent to that of bone, and approximately ten times that of the unreinforced ceramic.
Porous methyl methacrylate as an implant material
Authors: Taylor Duane F. , Smith Frederick B. 
Published: December 2004

AbstractRecent experience with a variety of materials in biomedical applications has demonstrated the importance of material form and shape in determining tissue response to implants. An investigation was made of the effect of pore size on the response of loose connective tissue to porous methacrylate implants. With appropriate pore size, vascular penetration and collagen deposition within the implants were observed to proceed rapidly.
Co‐permeant enhancement of drug transmission rates through silicone rubber
Authors: Most Clark F. 
Published: December 2004

AbstractIn vitro transmission rates of benzocaine were measured to determine the feasibility of augmenting the permeability of silicone rubber implants by introduction of co‐permeant plasticizers into the systems. It was shown that permeation can be enhanced or inhibited depending on the co‐permeant used, including increased mass transfer of methylene blue, previously reported to be a non‐permeant. Factors influencing such potentiation or diminution are thought to be solubility relationships among all components present, diffusivity, molecular volumes and mobilities of the co‐permeants, hydrogen bonding capabilities, and potential for internal segmental motion of polymeric plasticizers.
Hypoeutectic gold‐cobalt alloys for dental castings
Authors: Gettleman Lawrence , Harrison James D. , de S. Brasunas Anton 
Published: December 2004

AbstractHypoeutectic alloys of the Au‐Co system were studied for use in dental castings. Microhardness and tensile data were determined for annealed and aged alloys of compositions from 0.5 to 10 at. % Co in Au. Maxima for this alloy of HK 119, elongation 23% in 10 mm, yield strength of 185 MN/m2 (0.2% offset) and tensile strength of 257 MN/m2 occurred following aging at 350°C for 15 min. The system is considered promising for use as a dental casting gold alloy.
Glass ceramic bone implants. A light microscopic study
Authors: Greenlee T. K. , Beckham C. A. , Crebo A. R. , Malmorg J. C. 
Published: December 2004

AbstractGlass ceramic implants containing 45% SiO2 with a Ca/P ration of 5 become firmly fixed to bone when placed in a cortical defect of an intact rat femur. The addition of fluoride ions to the implant prevents this fixation. The most significant difference between the two compositions is in their solubilites. The presence of high local concentractions of Ca and PO4 ions at the interface of the soluble non‐fluoride containing implant, could account for the deposition of bone at its surface.It is not felt from these studies, however, that this model will be usable as a mass screening tecunique for evaluating materials variables. It is felt that other less laborous in vitro systems need to be devised.
A thoracic percutaneous lead system: Development and evaluation
Authors: Al‐Nakeeb Shaheen , Pearson Phillip T. , Cholvin Neal R. 
Published: December 2004

AbstractA thoracic percutaneous lead system was designed for use in present and future cardiac research in Biomedical Engineering. The lead system was fabricated of Teflon and silicone rubber and was implanted at the junction of the middle and upper third of the left sixth intercostal space of 24 mongrel dogs and observed for variable periods of time. Minimal inflammation was elicited in the skin and subcutis of 17 dogs, but infection and other complications developed in 7 dogs. The reaction of the ribs to the Teflon conduit was characterized by extensive periosteal new bone formation. The pulmonary and pleural reaction to silicone rubber tubing was also studied.
Comparison of the in vitro and in vivo tarnish of three gold alloys
Authors: Burse A. B. , Swartz M. L. , Phillips R. W. , Dykema R. W. 
Published: December 2004

AbstractNumerous laboratory studies have been conducted in an effort to determine the susceptibility of dental alloys to tarnish and corrosion.1–8 These investigations have embodied a variety of storage media, storage times and the influence of variables such as the presence of dissimilar metals. However, there is little in vivo data to establish the validity of the various in vitro tests with respect to their efficacy in predicting the susceptibility of the respective alloys to tarnish in the oral environment.It was the purpose of this research to compare the tarnish of three gold alloys as assessed by an in vitro test with the in vivo tarnish of the same alloys.
Environmental fatigue testing of silastic finger joint prostheses
Authors: Weightman B. , Simon S. , Rose R. , Paul I. , Radin E. 
Published: December 2004

AbstractHeat vulcanized silicone elastomer (Silastic‐Dow) has been in clinical use as a prosthetic replacement material for over a decade. When subjected to operating stress in body fluids, as in cardiac poppet‐valves, failure has occurred. Fractures of silastic finger‐joint prosthesis have also been experienced.Chemical and fractographic analyses of such failed finger‐joint prostheses raise the suspiciaon of failure. Severe discoloration of the implant at the point of maximal stress concentration, the presence of significant amounts of triglyceride and cholesterol on the fractured prostheses, and the pattern of fracture markings indicate that fracture was due to a combination of chemical surface deterioration and stress concentration.Study of the method of surgical insertion of these prostheses suggests failure to completely excise the volar plate and other palmar joint structures could create a step off and sufficiently increase the stress in the bending element of the device to cause fracture. In vitro cyclic testing at 37°C in serum failed to cause fracture of these devices after 10 million cycles, but did produce gradual discoloration of the entire prosthesis which began and was most noticeable at the point of bending. Although the prostheses adsorb lipid, which may produce surface deterioration, it is anticipated that properly inserted, the service life of these devices should be more than adequate for full clinical application.
Investigation of three‐surface properties of several metals and their relation to blood compatibility
Authors: DePalma V. A. , Baier R. E. , Ford J. W. , Gott V. L. , Furuse A. 
Published: December 2004

AbstractOrganic‐free specimens of 5 metals were prepared and characterized by parameters indicating their relative surface charge, surface texture, and surface energy prior to evaluation of their degree of thromboresistance. For the materials studied, there was no predictive correlation between the pre‐implatation electrical rest potentials and ultimate thromboresistance when standard prosthetic rings were placed in the canine inferior vena cava. Surface textural inhomogeneities greater thatn a micrometer or so made thrombus formation a certainty. There was a positive postimplantation correlation between the presence of a thin, labile, proteinaceous deposit on the prosthetic ring lumens and the passivation of the “high‐energy” materials towards thrombus accumulation. The metals which did consistently passivate, 316 Stainless Steel and Stellite 21, did so dynamically by acquiring an organic film within 2 hr after implantation. During continued residence in fresh, flowing blood these metals ultimately became dominated by an apparently monodisperse protein component of low critical surface tension. These findings were confirmed when thromboresistant pyrolytic carbon having initial surface properties similar to the metals but lacking reactivity and corrosivity was used as a comparison standard.
Development of blood compatible elastomers. II. Performance of avcothane blood contact surfaces in experimental animal implantations
Authors: Nyilas E. 
Published: December 2004

AbstractA family of materials referred to as Avcothane elastomers has been developed. These materials have displayed a considerable degree of blood compatibility both in vitro and in vivo, althous they do not contain any added anticoagulant and are not equipped with any suface charges in any manner.A member of this family the Avcothane‐51 elastomer, has rortinely delivered Lee‐White clotting times whose mean is close to 60 min. Long‐term aortic implantations of tubular prostheses made from this elastomer did not induce any pathological effects in swine. Results obtained in canine vena caval implantations and replacement appear to be consistent with the nonthrombogenic properties observed in vitro. This elastomer was utilized as the blood contact surface of the AERL Circular Assist Device which did not induce any significant intraluminal or intravascular thrombosis in acute implantations. An experimental model of a Left Heart Bypass Pump employing Avcothane‐51 surfaces throughout was tested in completely nonanticoagulated dogs for bypass periods ranging from 2 to 24 hr. Hematologic studies performed during these bypass periods indicated no prohibitive changes in blood composition. In the form of tri‐segmented Intra‐Aortic Balloon Pumps, the elastomer was chronically implanted in swine. The combined effects of the material and pumping of this device did not cause any significant thromboembolic or hemolytic effects which demonstrated its safe applicability to human implantations.
The epitaxy of Poly‐L‐alanine on L‐quartz and a glass‐ceramic
Authors: Hartwig B. A. , Hench L. L. 
Published: December 2004

AbstractThe effect of surface contamination on the morphology and orientation of poly‐L‐alanine on a glass‐ceramic and the (1010) and (1011) crystal faces of L‐quart is dealt with both microscopically and graphically. “Cleaning” with an r. f. plasma cleaner and contamination with pure nitrogen results in a change in the number of active sites with a corresponding change in the relative orientation of the polymer and the strength of bonding.
Thromboresistance of stellite 21: The role of an adventitious waxy contaminant
Authors: Baier Robert E. , Gott Vincent L. , Dutton Robert C. 
Published: December 2004

AbstractThromboresistance of the alloy most often used in artificial heart valves depends upon a hitherto unrecognized erosion resistant hydrocarbon coating. Contact angle measurements show the actual surface to be dominated by closely packed methyl groups as occur with adlineated aliphatic chains. The likely source for this layer is a tallow‐based compound from which adventitious components become tightly bound at the metal/air interface during final polishing. Here, as in other systems, the exposure of CH3 terminal groups correlates with significant blood compatibility.
Velour‐lined silicone rubber as an artificial bladder material
Authors: Stanley Theodore H. , Lattimer John K. 
Published: December 2004

AbstractAn ideal material for an artifical urinary bladder has not yet been designed. In order to study the effects of long‐term exposure of urine to velour‐lined Silastic silicone rubber, seven 80% cystectomized sheep had their natural bladders replaced with a Dacron velour‐lined, Silastic prosthesis. Animals were sacrificed 1 week, 3, 6, 9, and 18 months postimplantation of their prosthesis.While the luminal surface of the prosthesis one week after implantation had small isolated patches of epithelium on it none of the remaining animals had any evidence of tissue growth on this surface. No stones or calcifications were found on the luminal surface of the prostheis in any of the animals except the 18‐month survivor who had microscopic evidence of early calcification.The convex (serosal) surface of all the artifical bladders was covered with a thick connective tissue layer. At 9 months a muscle layer was seen in this tissue and it was clear the prosthesis was acting as a scaffold around which regeneration of the natural bladder was taking place. At 18 months after implantation regeneration of the natural bladder was complete and the prosthesis remained as a functionless, crumpled, hard foreign body in the lumin of the new bladder.It appears that velour‐lined Silastic silicone rubber though not ideal may be an effective artificial bladder material as long as it remains functional.
An immunospecific microbalance
Authors: Shons Alan , Dorman Frank , Najarian John 
Published: December 2004

AbstractA piezoelectric quartz crystal microbalance has been modified for the determination of antibody activity in solution. Antigen precoated crystals are exposed to antisera of varying concentration and specificity. Only antisera specific for the antigen precoat will form an additional protein layer on the crystal. The thickness of the antibody layer, measured by thefrequency shift of the crystal, is proportional to the concentration of specific antibody in solution. The technique provides a rapid qualitative and quantitative assay of antibody activity.
Perm‐selective dialysis membranes. II. Films based on acrylic acid‐n‐butyl methacrylate copolymers—a critical comparison with cellulose films
Authors: Muir W. M. , Gray R. A. , Courtney J. M. , Ritchie P. D. 
Published: December 2004

AbstractNew synthetic anionic membranes have been developed as replacements for the cellulose membranes currently used to remove blood toxins and water in hemodialyzers. The membranes are solvent‐cast on to polyethylene sheets from copolymers of acrylic acid with various alkyl methacrylates. Membranes from copolymers of acrylic acid and n‐butyl methacrylate show most promise as alternative hemodialysis membranes. The copolymers are prepared using modified emulsion copolymerization techniques with sequential monomeric additions in order to yield homogeneous polymers with the high molecular weight necessary for good film‐forming characteristics. Permeability of the synthetic membranes to blood components, rates of water removal by ultrafiltration, and mechanical properties of membranes are measured and compared with standard 150 and 300PT cellulose films. Results for cellulose films confirm previous conclusions that permeability is principally proportional to the inverse molecular volume of the diffusing solute, while new anionic synthetic membranes show selectivity to basic blood solutes and operate by an “assisted diffusion” mechanism. A method is reported of improving mechanical properties while maintaining high permeability rates for blood solutes and high water ultrafiltration rates, by treating membranes with ethylene oxide gas, a clinical sterilizing agent.