bluuebunny/crossref_metadata_2025 huggingface dataset:
The pressure dependence of the elastic constants of dental amalgam
Authors: Grenoble Dale E. , Katz J. Lawrence
Published: December 2004

The pressure dependence of the elastic constants of dental amalgam has been examined in the 0–50 kilobar range using a solid media, pressure apparatus coupled with an ultrasonic interferometer. Computer analysis of the measured longitudinal and shear ultrasonic wave velocities yields the pressure dependence of the bulk, shear and Young's moduli and Poisson's ratio. Samples were prepared with varying compositions from micro‐cut and spherical dental alloys. The elastic behavior of these samples can be directly related to the sample structure and composition as well as to the manipulation during preparation. In addition, an estimate can be made of the volume concentration of porosity.
The elastic constants of the constituent phases of dental amalgam
Authors: Grenoble Dale E. , Katz J. Lawrence
Published: December 2004

The 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

Advanced 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

Porous 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

The 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

A 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

The 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

Ceramic 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

The 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

Recent 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

In 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

Hypoeutectic 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

Glass 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

A 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

Numerous 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

Heat 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

Organic‐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

A 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

The 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

Thromboresistance 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

An 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

A 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

New 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.
Controlled release of testosterone using silicone rubber
Authors: Shippy Ronald L. , Hwang Sun‐Tak , Bunge Raymond G.
Published: December 2004

This study was undertaken to find a means for a long lasting and uniform release of the male hormone, testosterone. The rate of release of testosterone was determined over periods up to 4 months. The factors which affect the rate of testosterone release were studied and a mechanism for the release of testosterone was proposed.

The first means providing a constant release of testosterone was the use of silicone rubber membrane around testosterone cylinders. It was found that a constant rate of release was reached after an initial unsteady state period ranging from 1 to 2 weeks.

It was theorized that a water layer had formed between the membrane and testosterone cylinder. This layer caused the concentration inside the capsule to be that of saturated water.

Several testosterone cylinders were coated with especially prepared membranes. These membranes were made by dissolving testosterone and silicone rubber in a mixture of tetrahydrofurane and toluene. It was hoped that an amount of testosterone might be incorporated into the silicone rubber matrix. The samples were run and the permeabilities determined. The permeability showed little or no increase over the range of 10–30% testosterone.

Next, a membrane was prepared by mechanically mixing testosterone and silicone rubber. The amount of testosterone ranged between 5 and 200%, by weight. A definite increase in the permeability was observed with an increase in the percentage of testosterone.

The second method of obtaining a uniform rate of release of testosterone was by mechanically mixing testosterone and silicone rubber and molding a sheet. After an initial unsteady state a constant rate of release was obtained and such rate of release increased with higher percentages of testosterone in the sheets.
Biological tolerance of poly(N‐substituted acrylamides)
Authors: Kopeček J. , Šprincl L. , Bažilová H. , Vacík J.
Published: December 2004

The biological tolerance of poly(N‐substituted acrylamides) implanted subcutaneously to rats and pigs was investigated. Besides a macro‐ and microscopical evaluation of the implant and its surroundings, the surface changes of the implants were determined by means of a Stereoscan electron‐optical microscope;the results obtained confirmed the very good in vivo stability of the polymers used.

The histological analysis showed that all the polymers under investigation are very well tolerated by the organism and do not provoke any unfavorable reaction. The implants become surrounded with a granulation tissue which is gradually replaced by fibrocytes and collagen fibers situated in the basic substance staining positively with the alcian blue and PAS. In contrast with some authors we did not find a thicker capsule surrounding the implant on the sharp edges but on the flat planes. No calcification could be observed within the intervals investigated. The surface changes, which were studied electronoptically, were insignificant and connected with the way in which the implant was treated. No indications of malignant growth were observed.
Resorption rate, route of elimination, and ultrastructure of the implant site of polylactic acid in the abdominal wall of the rat
Authors: Brady John M. , Cutright Duane E. , Miller Robert A. , Battistone Gino C. , Hunsuck Ervin E.
Published: December 2004

This experiment describes resorption rate, light and electron microscopic appearance of the implant site, and tissue distribution and route of elimination of radioactivity from carbon‐labelled polylactic acid implants. Fifty‐six rats received abdominal implants and were serially sacrificed at 28, 56, 84, 112, 140, 154, and 168 days. Urine and fecal output was measured for radioactivity, along with implant site and several tissues at the time of sacrifice. Tissue distribution of activity was negligible. Resorption rate of the implant was linear with 63.2% remaining after 168 days. Elimination of radioactivity was via respiration, approximately 29.4% by this route. Histologically, the implant was invaded rapidly along septal defects or slowly on broad fronts. Invading cells were characterized either by large double‐walled vacuoles or by large accumulations of mitochondria and microvesicles adjacent to the implant surface. The long duration of this type of implant may be an important consideration in surgical applications.
Diffusion of pyrimethamine from silicone rubber and flexible epoxy drug capsules
Authors: Fu J. C. , Kale A. , Moyer D. L.
Published: December 2004

The rate of diffusion of pyrimethamine, a pyrimidine‐based antimalarial drug, from silicone rubber is compared to the diffusion of this drug from a flexible epoxy. Specific amounts of drug were mixed into the epoxy resin prior to the addition of an aliphatic diamine curing agent in the reparation of the epoxy‐drug capsules and into the silicone rubber prior to vulcanization with stannous octoate in the preparation of silicone drug capsules. These capsules, in the form of discs, were separately immersed in water which was replenished at regular time intervals. The amount of drug released was determined spectrophotometrically (λ max = 275 mμ). Silicone rubber discs with 20 mg of drug incorporated/disc showed a much higher initial release rate than epoxy discs with an equivalent amount of drug incorporated. The rate of drug release is shown to be a nonlinear function of the amount of drug initially incorporated. The amine functional groups on pyrimethamine, and the possibility of its participation in the curing of the epoxy is noted. In silicone rubber, such interaction is not expected. The addition of a silica filler to the epoxy drug mixture is associated with greater uniformity in the observed drug release rates of capsules made from the same batch of polymer drug mixture. The Shore A durometer hardness of these drug capsules are 30 and 70 for silicone rubber and epoxy, respectively.
Transport through crosslinked poly(2‐hydroxyethyl methacrylate) hydrogel membranes
Authors: Ratner Buddy D. , Miller Irving F.
Published: December 2004

The transport of urea and other biologically interesting solutes in aqueous solution across poly(2‐hydroxyethyl methacrylate) (p‐HEMA) hydrogel membranes has been studied. The results show that p‐HEMA membranes have a high permeability to urea due to a strong interaction between the polymer and urea, and, in addition, they are consistent with a pore flow model in which solute transport takes place through water‐filled regions essentially unaffected by the surrounding polymer matrix. The results indicate that such p‐HEMA membranes might be suitable for hemodialysis applications.
Poly(vinyl alcohol) hydrogels for synthetic articular cartilage material
Authors: Bray James C. , Merrill Edward W.
Published: December 2004

As part of a program to develop a synthetic articular cartilage material for use in reconstructive joint surgery, this paper is concerned with the desiderata for such a material and with the properties of poly (vinyl alcohol) hydrogels reinforced by crystallinity as developed for this purpose. Reference is further made to the ultimate preparation of cationic PVA hydrogels to provide the low‐friction lubrication necessary in a cartilage prosthesis when in contact with natural synovial fluid.
Preparation of dental alloy by splat cooling
Authors: Johnson Lewis B.
Published: December 2004

Splat cooling has been used for the preparation of dental alloy in the form of ribbons of 5–25 μm in thickness. The powdered alloy was produced by shaking the ribbons with a dental pestle in a mechanical amalgamator. One minute shaking produced a powder all of which passed a standard 400 mesh sieve. Only phases expected at room temperature have been produced thus far.
Porous segmented polyurethanes—possible candidates as biomaterials
Authors: Wilkes Garth L. , Samuels Sam L.
Published: December 2004

A systematic series of chemically well defined, segmented polyurethane‐polyether copolymers and their mixtures are shown to develop predictable and controlled morphologies. Changes in compositions and casting histories allow the preparation of polymer films with various types of morphological structures including uniform nonporous, coalesced spherulitic nonporous, spherulitic porous, and “Swiss cheese‐like” structures with uniform (but alterable) pore sizes.

The desirability of producing biocompatible materials with controlled morphologies provides incentive for further investigation of these and similar urethane copolymers.
Development of a toxicity evaluation program for dental materials and products. II. Screening for systemic toxicity
Authors: Lawrence W. H. , Malik M. , Autian J.
Published: December 2004

A series of systemic toxicity tests for various types of compounds are presented with illustrative data and discussed in regard to their relevance as potential screening tests for dental compounds and products. In developing and marketing a new dental material, it is important not only to ensure safety for the patient but also for the dentist, dental assistant, and laboratory worker who routinely handles and uses the product. Data are presented on a number of commercially available dental products as well as various chemical entities, which were tested by one or more of the methods described.
Plastics and inflammation: An in vivo experimental study
Authors: Rigdon R. H.
Published: December 2004

A significant variation occurred in the inflammatory response to polyethylene and polyurethane when embedded subcutaneously in experimental animals. This variation apparently is related to the composition of the plastic and adsorption of proteins. The attraction of polymorphonuclear leucocytes by plastics apparently is related to the electrostatic and/or electrokinetic imbalance that occurs at or near the site of implantation.

Polyurethane and polyethylene were selected for this study since preliminary observations had shown a variation in inflammatory response when they were embedded subcutaneously in the mouse. From this study it is evident that: (1) variations occurred in the inflammatory reaction in the subcutaneous tissue of mice and rabbits following the embedding of polyethylene and polyurethane; (2) polymorphonuclear leucocytes began to emigrate within hours after these two plastics were implanted, reaching their maximum number within 24 to 48 hr; (3) polymorphonuclear leucocytes usually were absent after the 6th experimental day in mice with polyurethane, but were present for 232 days in mice with polyethylene; (4) polymorphonuclear leucocytes were present in the rabbit for only a few days following subcutaneous implantation of polyethylene and polyurethane; and (5) leucocytes around the implanted polyurethane in the rabbit began to degenerate within 48 hr. The mechanism for this degeneration is not known.
A quick screening test of biomaterials by means of chick embryo techniques
Authors: Hulbert S. F. , Klawitter J. J. , Bartles D. M.
Published: December 2004

Many types of materials are being used as biomaterials, and there is a continuing search for more and better materials for specific pur poses. In this investigation, a new method was employed in screening materials in an effort to cut costs, save time, and have a worthwhile indication of the prospect of a new material. Samples of twenty gauge wires of stainless steel 316, stainless steel 304, Titanium 40, Vitallium, and copper were introduced into leg or wing muscles of 18‐day‐old chick embryos.

This was accomplished by opening the egg shell with a dental drill, implanting the material, and reclosing the shell. The chicks were allowed to hatch and were later sacrificed after eleven days, giving a total implant time of 14 days. This time period allowed for the acute inflammation that occurred during wound healing to subside. The sections were retrieved, embedded in epon 812, sectioned with a diamond saw, and histologically evaluated.

Copper was used for the negative control and showed the greatest adverse tissue response. Titanium 40 showed almost no response and stainless steel 316 showed very little. Stainless steel 304 exhibited a somewhat greater response than the stainless steel 316. All of the materials except wrought Vitallium used in this experiment gave predicted results.
Biocompatibility of poly(2,4‐pentadiene‐1‐ol)
Authors: Ulbrich K. , Šprincl L. , Kopeček J.
Published: December 2004

In our earlier papers1–4 we reported on the biocompatibility of esters and substituted amides of methacrylic and acrylic acids which are suitable for the development of specific biological functions.5 The results described in these papers1–4 enabled some relationships to be formulated which exist between the chemical and physical structure of the implants, on the one hand, and the process of their healing‐in and calcification, on the other.6.

A number of biological applications require materials having rubber‐like mechanical properties. With this aim we started in our laboratory the development of hydrophilic elastomers based on dienes containing hydrophilic groups. Poly(2,4‐pentadiene‐1‐ol)7 was the first polymer of this type obtained which had mechanical properties suited for biomedical applications. Its biocompatibility with living tissue is reported in this paper.
Formation of platelet aggregate emboli in a prototype hollow fiber membrane oxygenator
Authors: Dutton Robert C. , Edmunds L. Henry
Published: December 2004

We examined the formation of platelet aggregate emboli and factors that affect platelet aggregate formation and embolization in prototype hollow‐fiber membrane oxygenators used to perfuse dogs. Platelet aggregates formed on the inlet surface of the oxygenator. Many aggregates subsequently formed emboli which passed through the fibers and sometimes lodges in them. Aggregates also developed on the outlet surface. Aggregates that adhered to the oxygenator surfaces contained tightly packed platelets having multiple pseudopodia extracellular granules, and occassional fibrin strands and white cells. The number of platelet aggregate emboli found downstream to the oxygenator varied between 0 and 4 emboli/ml blood. These emboli did not contain fibrin and extracellular granules. Platelet aggregate formation and embolization was reduced or eliminated by increasing the dose of heparin or by using a circuit with a large priming volume of albumin solution and a large surface area oxygenator.
Metallographic examinations of retrieved intramedullary bone pins and bone screws from the human body
Authors: Gray R. J.
Published: December 2004

Substantial improvements have been made by the surgical manufacturing industry in the development of implants and by the orthopedic surgeon in the use of prosthetic appliances. In spite of these advancements, some prosthetic devices completely fail of do not provide satisfactory performance. Hostile environmental conditions of the human body are highly influential in limiting the service life of the implants, so the material selection and the design and fabrication must be made with extreme care. Examinations we have made of intramedullary pins retrieved from femurs reveal examples of fretting and/or crevice corrosion and in‐service failures that nucleated in microscopic surface gouges. Self‐tapping screws, essential for securing bone implants, failed due to fractures originating in the thread roots. Failures by merely exceeding the ultimate strength of the material and by the more involved process of stress corrosion cracking are shown.

An evaluation laboratory for failure analyses of prostheses is recommended.
Histochemical responses at a biomaterial's interface
Authors: Hench L. L. , Paschall H. A.
Published: December 2004

A series of nonporous glasses and glass materials designed with controlled surface ion activities to allow chemical bonding to bone are described. Surface reactivities of these materials in vitro are correlated with biological activities in vivo and in tissue culture. Direct chemical bonding of the materials to bone is demonstrated. The mechanism for development of this bond is through the production of an amorphous ion surface gel on the bioglass. This gel induces osteogenesis by a chemotactic response of osteoblasts.
Principles governing biomolecule interactions at foreign interfaces
Authors: Hoffman Allan S.
Published: December 2004

The adsorption, conformational changes, and desorption of biological molecules at foreign interfaces are effected by both kinetic and thermodynamic factors. The thermodynamic factors which drive the biomolecule/foreign interface system towards equilibrium include the enthalpy and entropy changes occurring during each step in the adsorption process. The principles governing interaction of proteins with nonwettable (nonpolar) and wettable (polar) foreign interfaces are discussed in terms of these thermodynamic parameters. Some examples to illustrate these arguments are presented are presented for plasma‐protein interactions on Silastic and radiation‐grafted hydrogel/Silastic interfaces.
Effect of stress on tissue ingrowth into porous aluminum oxide
Authors: Hulbert S. F. , Matthews J. R. , Klawitter J. J. , Sauer B. W. , Leonard R. B.
Published: December 2004

A study of the tissue compatibility of aluminum oxide implants under different stress conditions in rabbits was performed over four‐ and eight‐week implantation periods. The specific objectives were to examine endosteal bone ingrowth into aluminum oxide coneshaped plugs in amputated tibiae, while additional pellet‐shaped implants in the tibiae and femora of rabbits with amputated and nonamputated limbs were studied to determine: (1) if the degree of loading placed on the amputated limb was sufficient to promote bone activity, (2) the degree of inertness and/or toxicity of the aluminum oxide implants, and (3) a possible cause of bone spurs.

The results of the radiographic, histologic and microradiographic analyses of the in vivo implants demonstrated that there was little mineralized bone ingrowth into the coneshaped aluminum oxide implants in the amputated tibiae. The study also showed that the aluminum oxide pellet implants in the tibiae and femora of the nonamputated limbs demonstrated excellent mineralized bone ingrowth into surface and internal pores. By comparing these results with the incomplete ingrowth into corresponding pellet implants in the tibiae and femora of amputated limbs, it was determined that a lack of weight bearing and damage to the musculature and vascularity following amputation were interfering with the normal bone activity and therefore bone ingrowth.

Angiographs and radiographs of the amputated tibiae demonstrated that bone spurs were present and that they originated at the site of the periosteal damage. Their cause was believed to be associated with an increase in the vascularity of the adjacent tissues.
Surgical sutures and infection: A biomaterial evaluation
Authors: Edlich Richard F. , Panek Patricia H. , Rodeheaver George T. , Kurtz Leonard D. , Edgerton Milton T.
Published: December 2004

A standardized readily reproducible experimental model has been developed to assess the relative importance of the chemical and physical configuration of sutures as determinants of early infection in contaminated wounds. The chemical structure of the suture appeared to be the most important factor in the development of surgical infection. The incidence of infection in contaminated tissues containing either polypropylene sutures or nylon sutures was lower than the infection rate of tissues subjected to any other nonabsorbable suture. Among the absorbable sutures, polyglycolic acid (PGA) sutures evoked the least inflammatory response. The infection rate of contaminated tissues containing the PGA sutures was not significantly different from the incidence of infection of tissues subjected to the least reactive nonabsorbable sutures. The physical configuration of the suture played a relatively unimportant role in the development of early infection. The infection rate of contaminated tissues containing monofilament nonabsorbable sutures did not differ significantly from the incidence of infection of tissues subjected to multifilament sutures made from the same material. Coating the multifilament suture with either silicone, wax, or Teflon did not alter the incidence of early infection in the contaminated tissue. Finally, the presence of even the least reactive suture in contaminated subdermal tissue potentiated the development of infection.
Morphologic observations of neosheath development of undifferentiated connective tissue development around artificial tendons
Authors: Salisbury Roger E. , McKeel Daniel , Pruitt Basil A. , Mason Artur D. , Palermo Nicholas , Wade Clarence W. R.
Published: December 2004

The management of severe flexor tendon injuries of the hand has been dramatically improved by tendon sheath reconstruction with an artificial tendon, followed by conventional tendon grafting. The purpose of this study was to investigate the nature of neosheath formation.

In 25 chickens, the flexor tendons and sheaths in a toe were excised and replaced with a United States Army artificial tendon. An artificial tendon was also placed in the back, and four weeks later, tendons and surrounding tissue as well as normal tendon sheaths were excised and submitted for light, transmission electron microscopy and scanning electron microscopy.

In all instances, neosheaths formed around the silastic coated artificial tendon. The neosheaths formed in the foot and back were similar to normal sheath, having the same cellular and fibrous composition. Reconstruction of the normal anatomy with an artificial tendon explains why this surgical technique gives superior results to other less physiologic procedures in patients with severe hand injuries.
The mandibular staple implant for the atrophic mandible
Authors: Small Irwin A. , Metz Herbert , Kobernick Sidney
Published: December 2004

The mandibular staple is an endosseous implant that will permit the attachment of a lower deture in cases of severe alveolar bone atrophy. It is placed through a submental incision and inserted into seven parallel holes drilled into the mandible. A curved bar containing seven pins is inserted in the holes and is place against the inferior border of the mandibular symphysis. The two lateral most pins project into the mouth and the five retentive pins remain completely buried in bone. Two fasteners are screwed down on the threading of the intraoral pins. Later a bridge containing Dalbo attachments is cemented to the fasteners which allow attachment to a lower denture. A series of 25 patients have been completed with 20 successful patients for survival rate of 80%. The longest case has been in for five years and the average case has been in for 3 years. Stainless steel, titanium and ceramic coated titanium has been with apparently equal success. Patient acceptance has been excellent.
The present status of endosteal oral implants
Authors: Cranin A. Norman , Dennison Thomas A. , Schnitman Paul
Published: December 2004

This paper presents a review of 338 metallic endosteal oral implants of six designs that had been in situ for periods of up to seven years as observed by members of the Brookdale Group. Of the 338 impervious alloplastic endosteal implants studied, none but the endodontic endosteal implant demonstrated positive long range findings. It would appear that the eventual demise of endosteal implants is predictable on a basis of time.