bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vivo degradation of silicone rubber poppets in prosthetic heart valves
Authors: Cuddihy Edward F. , Moacanin Jovan , Roschke E. John , Harrison Earl C. 
Published: December 2004

AbstractDynamic shear modulus G′ was measured throughout the volume of three nonvariant silicone rubber poppets which were recovered from aortic prosthetic heart valves that had been implanted for 4 days, 52 days, and 8 years. Similar measurements were obtained for two unused silicone rubber poppets. Although the recovered poppets exhibited no obvious physical evidence of damage, the silicone rubber had undergone in vivo degradation throughout the poppet volume as indicated by decreases in modulus. The measurements also indicate that the poppet surface degrades at a rate faster than the core. Further, comparison with data reported in the literature suggests that the surfaces of variant poppets degrade at a rate faster than the surfaces of nonvariant poppets.
Prefabricated silicone subdermal mandibular implants: Observations and problems related to their application
Authors: Habal Mutaz B. , Chalian Varoujan A. 
Published: December 2004

AbstractSuccess in the use of custom‐fabricated Silastic implants in patients with facial contour defects led us to utilize this method in reconstructing mandibular defects. However, mandibular reconstruction with alloplastic material is quite difficult because of the presence of continuous stress and motion in that region. The evolution in the use of the mandibular implant from the commercially available one to the K‐wire reinforced, prefabricated, silicone implant was largely dependent on the availability of silicone and the ultimate result obtained.In the past few years, about 30 subdermal implants were inserted. Some of those implants were placed immediately into patients undergoing resection for tumor. The implant was prefabricated prior to surgery from x‐ray measurements of the anticipated segment to be resected; it was then used to reconstruct the defect prior to the final closure of the operative wound. Other implants were manufactured 6–18 months after resection for tumor or for deformity as a result of trauma. The implants were used to reconstruct the facial defects and to correct the functional abnormality, such as drooling or deviation of the affected side by the unstable mandibular segment. Patients with severe congenital malformation have soft tissue deficiency in association with their bony malformation. Therefore, implants in such conditions were doomed to failure.Patient selection is the key to successful implantation.
Oxidized orlon as a blood interface
Authors: Ross J. N. , Wright J. T. M. , Eskin S. , von Koch L. , Normann N. A. 
Published: December 2004

AbstractPolyacrylonitrile fabric (Orlon) may be oxidized by heating in air, when it becomes black and carbonized. During the heat treatment, the fibers shrink; this shrinkage allows components such as diaphrams to be shaped around molds. Oxidation reduces the tensile strength by about 25% and also reduces the stiffness of the material.The oxidized Orlon was screened in tissue culture for possible cytotoxic effects. Finding none, patches of the material were sutured into the right atrium of dogs and examined after 48 hr. Because of encouraging results, 10 atrial patches, consisting of Dacron velour and oxidized Orlon side‐by‐side, were implanted into the right atrium of dogs. Five patches were backed with Silastic to render them impervious, and five with segmented polyurethane. The atrial patches were examined after 48 hr, and in all instances the oxidized Orlon part of the patch was coated with a thinner and smoother fibrin layer than was the Dacron velour half.A left ventricular bypass pump was fabricated from oxidized Orlon and spraycoated on the nonblood surface with segmented polyurethane. After 48 hr implantation in the chest cavity of a calf, pumping without systemic anticoagulation, the pump was found covered by a thin, smooth, firmly attached layer of fibrin.
Poly(methyl methacrylate)–aqueous phase blends: In situ curing porous materials
Authors: de Wijn J. R. 
Published: December 2004

AbstractA potential implant material has been developed which combines the advantages of curing in situ and an open porous structure. This paper deals with synthesis and characterization of the material, which is a modification of the well‐known acrylic bone cements. Some early results of animal experiments are mentioned.
Biomaterials and collagen synthesis
Authors: Cohen I. Kelman , Diegelmann Robert F. , Wise William S. 
Published: December 2004

AbstractA highly reactive biomaterial (clay) and a relatively nonreactive substance (silicone) were implanted separately in primarily closed incisions on the backs of rats. Collagen synthesis was determined in biopsies from each test site after 8 days. The biochemical measurements of collagen synthesis showed a significant correlation with the gross pathologic and histologic findings.
Development of blood‐compatible elastomers. V. Surface structure and blood compatibility of avcothane elastomers
Authors: Nyilas E. , Ward R. S. 
Published: December 2004

AbstractThe Avcothane 51 elastomer, a member of a series of proprietary materials best characterized as polyurethane/poly(dialkylsiloxane) block copolymers, displays considerable hemocompatibility without any incorporated anticoagulants. In the form of intra‐aortic balloons, the elastomer was implanted in several thousands of cardiac patients without intolerable hematologic effects. Hemocompatibility has been assumed to result from a predominantly dispersion‐type surface force field whose intensity fluctuates within small domains, maintaining adsorbed blood proteins in an unstable state. The relative hemocompatibility of films, which were obtained from a prepolymer solution cast on substrates impenetrable to the solvent, is a function of the effective surface molecular structure. This can vary as a function of preparative conditions (temperature and rate of evaporation), and has been correlated with an anisotropic distribution of the silicone component in cured films. The concentration of this component in surface layers was quantified independently by IRATR spectroscopy and electronmicroprobe analysis, giving consistent results. An IRATR index, which is computed from the ratio of absorptivities measured at 13.00 and 12.62 μ and is inversely proportional to the relative silicone content of surface layers, was found to correlate with the apparent hemocompatibility determined by different in vitro methods. Optimized reproducible hemocompatibility is attained by strict process controls.
Interaction of living cells with polyionenes and polyionene‐coated surfaces
Authors: Rembaum A. , Senyei A. E. , Rajaraman R. 
Published: December 2004

AbstractPolyionenes have been shown recently (A. Rembaum, Appl. Polym. Symp. No. 22, 299, 1973) to produce the following biological effects: (1) bactericidal action, (2) formation of insoluble complexes with DNA and heparin, (3) neuromuscular blocking action, (4) cell aggregation and lysis, and (5) cell adhesion.In the present study, polyionenes of various structures (mainly I3,3, I6,10) were used as molecular probes to gain an understanding of the cell surface phenomena of adhesion on glass‐ and polyionenes‐treated surfaces. Since tumor cells show different surface cell properties, including an increase in the anodic mobility, they bind preferentially to polyionene‐treated surfaces. Normal human diploid WI‐38 cells were found to adhere at a lower rate than SV‐transformed WI‐38 cells. However, cell spreading was accelerated in both cases.A study of the interaction of polyionenes in solution in vitro and in vivo and polyionenes covalently bound to polymeric microspheres with leukemic murine EL 4 cells and normal thymocytes showed specific cytotoxity towards the leukemic cells.
Histological reaction to various conductive and dielectric films chronically implanted in the subdural space
Authors: Loeb G. E. , Walker A. E. , Uematsu S. , Konigsmark B. W. 
Published: December 2004

AbstractThirty different test patches of various thin film materials were chronically implanted in the subdural space of cats to determine their suitability as components for proposed neuroprosthetic devices. In particular, materials employed by the microelectronics industry were screened, and reactions were found to be quite dependent on specific formulations or surface preparations of otherwise similar materials. A nonspecific but severe complication of pressure necrosis under thin films that spontaneously roll and curl in vivo was noted.
A new antithrombogenic heparinized polymer
Authors: Miyara Hajime , Harumiya Noriho , Mori Yuichi , Tanzawa Hiroshi 
Published: December 2004

AbstractA new antithrombogenic polymer was synthesized by photoinduced graft copolymerization of both a hydrophilic polymer and a cationic polymer to hydrophobic poly (vinyl chloride) copolymer, and by quarternizing and heparinizing the obtained graft copolymer.For polymers of various compositions obtained by the method described above, chemical composition, water absorption, membrane potential, and quantity of adsorbed heparin were determined and antithrombogenicity evaluated in vivo. Thus, it has been found that the polymer of excellent antithrombogenicity has a negative membrane potential, a moderate elution rate of heparin, adsorbs heparin in a quantity of approximately 15 wt‐%, and has a degree of water adsorption of about 30 wt‐%. Also, measurement of membrane potential was very useful for the estimation of the quantity of the adsorbed heparin and its change with time.
Polytetrafluoroethylene–N‐Vinylpyrrolidone graft copolymers: Affinity with plasma proteins
Authors: Boffa G. A. , Lucien N. , Faure A. , Boffa M. C. , Jozefonvicz J. , Szubarga A. , Mandon P. , Larrieu M. J. 
Published: December 2004

AbstractN‐vinylpyrrolidone was grafted onto films, grains, and tubes of polytetrafluoroethylene (PTFE) using a radiation procedure. By controlling the experimental conditions, it was possible to obtain an analogous grafting percentage on films and grains. Kinetic grafting onto a tube might be used under certain conditions to preserve both size and water tightness. Poly(vinylpyrrolidone) (PVP)‐grafted material became hydrophilic and slightly swollen according to the grafting percentage obtainedA scanning electron microscope (SEM) analysis of polymer surfaces showed preferential polymerization sites at a low radiation dose. A regular, velvet‐like surface was obtained for a high grafting percentage induced at a low radiation intensityBiological properties of PTFE were compared before and after PVP grafting. PTFE appeared to be a nonreactive polymer with respect to the blood‐clotting proteins. No significant change was observed using different granulometric sizes of PTFE grains, and its noteworthy inertness was preserved after PVP graftingInteractions between polymer surfaces and human plasma proteins were analyzed using 125I‐isolated proteins. Fibrinogen and immunoglobulins have a high affinity for PTFE; on the other hand, albumin was weakly adsorbed on the polymer surfaceMarked changes in protein adsorption were observed after PVP grafting. Hydrophilic group grafting induced an increase of albumin adsorption and a decrease of fibrinogen adsorption. Prothrombin affinity was not significantly affected by modified PTFEStudies of serum protein adsorption using solid‐phase radioimmunoassays were developed with monospecific and polyvalent antisera. After incubation of the whole serum protein and polymer, immunoglobulins were found to exhibit the major part of bound protein radioactivity on the polymer surface. No evidence of increasing adsorption of immunoglobulins from rabbit serum after immunization by PTFE or PTFE/PVP was observed. The immunoglobulin adsorption was submitted to a copetitive effect with the other serum proteins. It was possible to postulate the competitive action of albumin, particularly after biological property change induced by chemical grafting.
Fabrication of large arrays of cortical electrodes for use in man
Authors: Klomp G. F. , Womack M. V. B. , Dobelle W. H. 
Published: December 2004

AbstractTechniques are described for fabrication of electrode arrays for stimulation and/or recording from a human cerebral cortex. These arrays may be neurosurgically inserted (with or without a Penrose drain) in the course of a conventional craniotomy or craniectomy, and are easily removed without reopening the ineision. Termination of the connecting wires in a special percutaneous pedestal has also permitted chronic implantation. The contacts and connecting wires are made of pure platinum embedded in a Teflon ribbon‐cable matrix. The choice of materials combines biological acceptability, electrochemical stability, and integrity of the insulation, but imposes special fabrication procedures.
Porous acrylic cement
Authors: Rijke A. M. , Rieger M. R. , McLaughlin R. E. , McCoy S. 
Published: December 2004

AbstractThe use of acrylic bone cement has a number of shortcomings, viz., high curing temperatures that can cause thermal necrosis, release of toxic monomer, and a less than perfect cement‐to‐bone bond. However, by modifying the cement composition through the addition of a soluble, nontoxic filler such as sucrose or tricalcium phosphate which does not impair the workability of the material during surgery, a significant improvement in the performance of the cement can be achieved.Because the filler replaces part of the acrylic components, less heat is generated during curing while the filler itself acts as a heat sink. Also, less monomer, proportional to the amount replaced by the filler, diffuses from the implant site.Upon elution of the filler, a porous cement will be obtained provided that a critical minimum percentage loading is exceeded so that the filler crystals will make physical contact with each other. The value of this percentage depends on both crystal modification and size. In the 125–175 μm sucrose crystal size range, the critical minimum percentage lies in the range of 20–28 wt % loading. Above 30%, the interconnecting pore size increases sharply to a value which allows good tissue ingrowth into the pores.The introduction of filler and pores causes a drop in strength, but the diametral tensile strength of modified cement containing up to 40% pores and sucrose lies between .7 and 1.5 kg/mm2, respectively, which is still in the same range as that of bone.
Human platelet and fluorochemical interaction
Authors: Kmetzo James J. , Peter Stein T. , Wallace Herbert W. 
Published: December 2004

AbstractSince the fluorochemicals have become of interest for the development of artificial red blood cells, oxygenators, liquid breathing, and as a radiographic contrast medium, their interaction with biological substances is of importance. Fresh human platelets were placed in contact with four different fluorochemicals for a period of 50 min. The platelet function as measured by aggregation was determined before and after fluorochemical contact. Appropriate controls were also evaluated. No significant differences were found between the aggregation of platelets contacted with fluorochemicals and the aggregation of platelets from the same donor unexposed to fluorochemicals.
Clinical influences on bone cement monomer release
Authors: Bayne Stephen C. , Lautenschlager Eugene P. , Greener Evan H. , Meyer Paul R. 
Published: December 2004

AbstractMonomer losses for two self‐curing acrylic cements were similar via laboratory serial weighing experiments. Both the P/L ratio and mixing duration substantially influenced subsequent monomer losses, but ambient temperature variation during mixing had little effect. Greater losses were encountered during the mixing and setting intervals than during the molding interval. Patient potential exposure to monomer occurs during the molding and setting intervals; therefore, handling procedures reducing losses in these intervals are important to the surgeon.The least monomer loss during both molding and setting occurred at the manufacturers' recommended P/L ratio, which strongly indicated the need to mix all contents supplied. Mixing loss increased with amount of spatulation. However, once the mass was well mixed (about 300 steady spatulations), no further decreases in the molding and setting interval losses were promoted by overmixing. Because of the lower monomer loss rate during the molding interval, postponed cement insertion may not be warranted in light of losing mechanical locking efficiency. The actual ramifications of a threefold reduction in potential patient exposure (3.5 down to 1.2 wt % of total monomer) via modified handling techniques have not yet been clinically evaluated.
Histologic response to porous PMMA implant materials
Authors: Nathanson Dan , Gettleman Lawrence , Schnitman Paul , Shklar Gerald 
Published: December 2004

AbstractPoly(methyl methacrylate) as used in polymer replica tooth implants was fabricated into 6 × 6 mm cylindrical specimens and cured in either an air oven, pressure pot, autoclave, or microwave oven. Polymer porosity was achieved by means of either (1) intrinsic foaming agents, or (2) compacting different sizes of large beads with a minimum of monomer, with dense PMMA used as a control. Specimens were then implanted in the long bones of baboons.Histology of thin‐sectioned and ground specimens from the sacrificed animals revealed complete tissue ingrowth into implanted material made of medium and large PMMA beads, very superficial ingrowth into material containing foaming agents and anorganic bone chips, and no ingrowth into dense PMMA implants.None of the implants were rejected or caused chronic inflammation. The effect on histologic response of the different curing methods could not be distinguished.
The biocompatibility of materials for internal fixation of fractures
Authors: Brown Stanley A. , Mayor Michael B. 
Published: December 2004

AbstractSurgically produced fractures of rabbit tibiae were internally stabilized with in tramedullary rods of stainless steel (316LVM), titanium (6A1,4V), polyacetal (Delrin), and polyamide (Nylon 101). Periodic radiographs were taken until sacrifice at 16 weeks after fracture. Structural properties of the tibiae were determined in torsion with the rods in situ, and then the tissue was prepared for histology or microradiography.The results demonstrated that fracture remodeling was adversely affected by the metal rods. New bone was seen to have formed over the ends of the metal rods, and cortical bone resorption was observed in the fracture region, suggestive of transfer of mechanical stress to the rods, resulting in stress shielding of the diaphysis. Negligible osseous response to the polymeric rods was observed; fracture callus remodeling was extensive. The torsional test results demonstrated that fractures with polymeric rods were significantly stronger and tougher than those with metallic rods. With the exception of titanium, the strength of healed fractures was inversely related to the elastic moduli of the implant materials.
Neurocranial reconstruction using an elastomer‐coated cloth mesh and bone grafting
Authors: Leake D. , Habal M. , Maniscalco J. , Freeman S. 
Published: December 2004

AbstractThe purpose of this report is to present our 5‐year experience in reconstructing large bony defects in the cranial vault of 16 patients. The method employs an alloplastic implant device made of elastomer‐coated cloth mesh, used in conjunction with bone grafting [D. L. Leake and M. Habal, J. Biomed. Mater. Res., 10, 555 (1976)]. The cranial defects ranged in size from 6 × 6 cm to 15 × 17 cm. The defects were in the frontal, temporoparietal, and occipital regions. Particularly challenging was the frontal‐orbital region involving the superciliary ridges. The alloplastic implant provides controlled contour of the bone graft material while providing strength and stability during healing. The implant has adequate but not complete rigidity, allowing adaptability in the operating room. The elastomer used is a polyetherurethane. Any biocompatible cloth mesh can be used, but Dacron [poly(ethylene terephthalate)] was chosen because of its extensive implant history.Contrasted with reconstruction using only bone, where as many as half of the cases had uneveness and were found to be aesthetically unsatisfactory, the technique described here has resulted in aesthetically excellent results and an intact neurocranium in the 16 patients studied thus far.
Stress relaxation of dental amalgam alloys
Authors: Huget Eugene F. , De Simon Laszlo B. , Hertert Robert S. 
Published: December 2004

AbstractShort‐term stress relaxation of four dental amalgam alloys was studied. Test materials included two conventional lathe‐cut restoratives, a spherical alloy, and a dispersed phase product. Specimens were 24‐hr‐old 4 × 8‐mm cylinders. The specimens were compressed and held at constant strain on development of a stress (S0) of 28 MN/m2. Subsequent stress relaxation (Dt) was recorded for 60 sec. Data were obtained at eight nominal temperatures between 0 and 55°C.Over the experimental temperature range, fractional stress losses at 60 sec (Dt/S0/60) for specimens made from lathe‐cut alloys increased from 10% to 58%. The spherical material and the dispersed phase alloy showed fractional stress losses (Dt/S0/60) ranging from 9% to 47% and 9% to 31%, respectively.It would appear that particle morphology and alloy composition affect stress‐relaxation behavior of dental amalgam. Stress decay patterns enhance significantly the mechanical characterization of amalgam alloys.
Surface texture and strength of vitreous carbon–poly(methyl methacrylate) dental implant materials
Authors: Hodosh Milton , Gettleman Lawrence , Shklar Gerald , Povar Morris 
Published: December 2004

AbstractA study has been carried out on the surface texture and the strength of several dental implant materials composed of vitreous carbon microballoons (6, 24, and 48 wt %) and poly(methyl methacrylate). Two sizes of microballoons were used—particle size less than 100 μm and particle size greater than 100 μm. Square wafers of the materials (10 × 10 × 1 mm) were studied with the surface sandblasted in half of the specimens. SEM studies revealed a rough porous surface with scattered moderately sized deep cavities in the 6% and 24% specimens with an increase in the number of cavities in the 24% specimens. The 48% specimens revealed a rough, porous surface composed of large shallow craters.Prepared specimens of the materials, processed by a gas‐fired air oven and by a microwave oven, were tested for compressive strength and tensile strength using an Instron Universal Testing Machine. Compressive strengths of the various mixtures were similar, but mixtures using VC particle size over 100 μm demonstrated somewhat reduced compressive strength. Tensile strengths of the mixtures decreased significantly as the amount of VC increased, with a 20% reduction at 24 wt % and a 45% reduction at 48 wt %.
Adsorption of plasma proteins on hydrophobic surfaces. II. Fibrinogen and fibrinogen‐containing protein mixtures
Authors: Bagnall Robert David 
Published: December 2004

AbstractThe adsorption of fibrinogen from single solution and from mixed solution with albumin and γ‐globulin has been followed at the air–buffer, isooctane–buffer, and methylene iodide–buffer interfaces by the pendant drop technique. Fibrinogen is shown to form substantial coherent films on isooctane and methylene iodide, suggesting considerable unfolding and lateral association. From this, a novel hypothesis has been proposed to account for the dominance of fibrinogen adsorption from mixed solutions on certain hydrophobic surfaces, in which the spreading pressure of rapidly unfolding fibrinogen molecules is sufficient to desorb other plasma proteins.