bluuebunny/crossref_metadata_2025_split huggingface dataset:
Slow crack growth in acrylic bone cement
Authors: Beaumont Peter W. R. , Young Robert J. 
Published: December 2004

AbstractSlow crack growth in Perspex acrylic sheet (PMMA) and Simplex acrylic bone cement in air and water has been studied from a fracture mechanics viewpoint. It has been found that the crack velocity, V, for each material depends upon the intensification of stress at the tip of the crack. Experimental measurements have been made of V as a function of the stress intensity factor, K, at the crack tip, and a derived V, K relationship has been used to predict the times‐to‐failure of components made from PMMA and Simplex cement. Direct measurements of time‐to‐failure for PMMA have shown that the predicted values give a conservative estimate of the structural lifetime of the material.
Thermodifferential analysis of ceramic implants
Authors: Cini L. , Pizzofferrato A. , Trentani C. , Sandrolini S. , Paltrinieri M. 
Published: December 2004

AbstractCeramic pelletes (in Al2O3 92% and in calcium aluminate) implanted into the muscles of rabbits for varying periods of time, and samples of similar material, not implanted but mixed with organic substances, have been analyzed by means of thermal differential analysis (TDA).Which hydrated calcium aluminates are formed from implants after contact with the tissure fluid, has been established.It has also been ascertained that the ceramic implants absorb organic substances from the tissue fluid, which, from a first evaluation, seem to be composed of simple molecules.The results of this initial inquiry have provided positive indications of the utility of TDA to assist in elucidating the phenomena that occur between implant and tissue.
Viscoelastic properties of human dentin
Authors: Korostoff Edward , Pollack Solomon R. , Duncanson Manville G. 
Published: December 2004

AbstractStress relaxation measurements were performed on thick‐walled cylinders of radicular human dentin. The experimentally measured relaxation moduli were used to obtain an approximation to the logarithmic distribution functions of relaxation times. This distribution function was used to predict the behavior of other viscoelastic properties. In particular, the prediction of the strain and strain rate dependence of the modulus was determined and compared with experimental results.
An ultrastructural study of the biocompatibility of poly(2‐hydroxyethyl methacrylate) in bone
Authors: Murray David G. , Dow Jo‐Anne Sessa 
Published: December 2004

AbstractBecause of the unique properties for swelling in a fluid medium and variable modulus of elasticity, hydrophilic methacrylates may be of potential usefulness for implanting prosthetic devices in bone. To investigate the biocompatibility, electron micrographic studies were done on specimens of poly(2‐hydroxyethyl methacrylate) imbedded in bone for varying periods of time. Ultrastructural examination revealed progressive ossification of surrounding connective tissue up to the tissue polymer junction over a 6 month period. There was no evidence of inflammatory response. Based upon this study, it would appear that bone adjusts to an implant of hydrophilic methacrylate by ossification to the implant junction. This supports continued studies into the usefulness of this material as an implant.
Surface hydroxylation of styrene–butadiene–styrene block copolymers for biomaterials
Authors: Sefton Michael V. , Merrill Edward W. 
Published: December 2004

AbstractThis work pertains to the development of high strength elastomers potentially useful as nonthrombogenic cardiovascular prostheses. Triblock copolymers of the styrene–butadiene–styrene type have been subjected to surface hydroxylation which provide reactive sites at the surface for the subsequent coupling of heparin while retaining the unique mechanical properties of the SBS copolymers. Curves of hydroxyl content versus the copolymer film thickness demonstrate the effect of swelling in the surface region on the product distribution and on the time dependence of the hydroxylation process. In addition, the effect of time, temperature, and the composition of the reaction bath on the diffusion/reaction process is shown. Finally, the general applicability of this surface modification scheme to the development of biomaterials is discussed.
Canine tendon studies. II. Biomechanical evaluation of normal and regrown canine tendons
Authors: Walker P. , Amstutz H. C. , Rubinfeld M. 
Published: December 2004

AbstractSome of the mechanical properties of regrown canine tendons are compared to those of normal tendons of young and mature animals. Patellar and Achilles tendons from 12 beagle dogs were removed and studied with their bone origin and insertions. Mechanical tests were performed within 24 hr and test conditions simulated the physiological function of the tendon in vivo at room temperature. Specimens were soaked in Ringers solution and mounted in an Instron testing machine with load deflection curves plotted automatically. The parameters used for analysis were load extension, stress relaxation, elastic limit, and strain rate dependence.The regrown tendons in young animals appeared to quickly adjust in dimension and structure so that their properties were not significantly different from those of normal tendons on a load extension basis.The normal tendons were stiffer than regrown ones but the modulus of elasticity increased with age. The Achilles were stiffer than patellar tendons. Cyclic loading with 25 kg did not affect reconstructed tendon models, although some increase in stiffness was noted. The elastic modulus decreased with an increase in ambient temperature and increasing strain rate.
Influence of application technique on microstructure and strength of acrylic restorations
Authors: Kusy R. P. , Mahan J. R. , Turner D. T. 
Published: December 2004

AbstractAn investigation was made of the influence of application techniques on the microstructure and properties of an acrylic tooth restorative. Mixtures of acrylic powder and monomer (“Sevriton Simplified”) were applied by the brush technique of Nealon (J. Prosth. Dent., 2, 513, 1952) and by two bulk flow techniques. While similar porosities (about 4%) were observed, the brush technique resulted in a greater quantity of grains from the acrylic powder. Despite this, there was little difference in values of compression modulus, compressive yield stress, and diametral compressive strength.The mechanical strength of the materials studied was less than one‐half that of high molecular weight poly (methyl methacrylate) (PMMA). Crack propagation studies established that the interface between the grains and matrix was not a source of weakness. However, as the matrix was crosslinked this could not be checked by solution methods of polymer characterization.
Growth of cultured calf aortic smooth muscle cells on cardiovascular prosthetic materials
Authors: Eskin S. G. , Armeniades C. D. , Lie J. T. , Trevino L. , Kennedy John H. 
Published: December 2004

AbstractThe growth of cultured calf aortic smooth muscle cells on cardiovascular biomaterials was investigated, using native and oxidized polyacrylonitrile (orlon) fabrics, dacron velour, and Parylene‐C coated polypropylene microfabric as substrates. By light microscopic evaluation, surface cell coverage was most complete on microfabric, followed by native orlon, dacron velour, and oxidized orlon. Native orlon supported the greatest total cell growth, as determined by chemically extractable protein, followed by oxidized orlon, dacron velour, and the microfabric. The observed differences appear to be related to the pore size and fiber thickness of the different substrates.
A Dacron wool packed‐bed extracorporeal reactor: A kinetic study of immobilized Escherichia coli II L‐asparaginase
Authors: Ko R. Y. C. , Hersch L. S. 
Published: December 2004

AbstractAn extracorporeal reactor containing a packed bed of Dacron fibers has been developed. Escherichia coli II L‐asparaginase was coupled to the Dacron using γ‐aminopropyltriethoxysilane and glutaraldehyde. The preparation had an activity of 37 IU per gram of Dacron (37°C). The apparent Km was studied as a function of the flow rate. The data indicated that the apparent Km approached the Km of the native enzyme at floe rates of about 300 ml/min. In vivo use of L‐asparaginase immobolized on the Dacron indicated effective lowering of Plasmatic L‐asparagine levels.
Hyaluronidase‐bound membrane as a biomaterial for implantable fuel cells
Authors: Ahn B. K. , Wolfson S. K. , Yao S. J. , Liu C. C. , Todd R. C. , Weiner S. B. 
Published: December 2004

AbstractA new biomaterial containing covalently bound hyaluronidase was prepared. An application of this enzyme membrane is to improve the performance of an implantable fuel cell. Hyaluronic acid is a contributor to the viscosity of tissue fluids but can be a potential fuel source because of its sugar content. The incorporation of immobilized hyaluronidase would not only contribute to a more available fuel supply by splitting hyaluronic acid but, perhaps more importantly, enhance the rate of mass transport of fuel, O2, and reaction products by reducing the viscosity near the electrode membranes. Hyaluronidase was bound to Sepharose gel and its thermoplastic membrane after activation by cyanogen bromide. Fourteen and 22% of the activities were recovered from the gel and membrane, respectively. The activity of the bound enzyme was stable for six months at 0°C. The addition of hyaluronic acid, 1 mg/ml, to a typical implantable type bioautofuel cell in vitro increased external solution viscosity from 1.1 to 2.5–2.8 cP and reduced voltage output under 10 kΩ by 60% in 3 hr. When the hyaluronidase bound membrane was placed at the anode, viscosity of the glucose–hyaluronic acid solution was lowered to 1.8 cP and the cell output increased to the original level of a glucose‐fueled cell in 3 hr. Glucosamine‐equivalent released from hyaluronic acid at the electrode was 3.1 mg after 22.5 hr. This represents 90% of the theoretical consumption. Restoration of the cell output was probably a combination of the enhanced transport of fuel, O2 and products, and/or appearance of a new fuel, glucosamine‐equivalent.
Some new studies of the wear behavior of ultrahigh molecular weight polyethylene
Authors: Rostoker W. , Galante J. O. 
Published: December 2004

AbstractThe wear rate of ultrahigh molecular weight (UHMW) polyethylene over a long campaign of sliding distance is not constant. Both unfilled and graphite filled polyethylene show a high rate early, which reduces to a low value. The graphite‐filled product shows a late stage increase in wear rate. Increased molding temperature reduces the molecular weight and increases the wear rate. Titanium articulating with UHMW polyethylene develops frequently an abnormally high wear rate with the generation of a black wear product.
Preliminary observations of bone ingrowth into porous materials
Authors: Robertson Diane M. , St. Pierre Leon , Chahal Ramlal 
Published: December 2004

AbstractA preliminary investigation has been performed (a) to determine the kinetics of bone ingrowth into porous materials and to determine if this ingrowth could be catalyzed by the presence of a foreign substrate; and (b) to measure the bonding capability of bone with a porous‐surfaced metallic implant.Tests on porous‐surfaced implants corroborate the work of other investigators in showing that bony tissue will grow into a porous substance that has pores large enough to support tissue nourishment. The shear strength of the bone–implant interface appears to increase with pore size and time of healing. Furthermore, it may be possible to catalyze this tissue ingrowth by the introduction into the fracture site of a foreign substance; in this experiment, glass beads 200–290 μ in diameter were used.
The effects of pylon shape on bone–pylon interface performance in direct skeletal attachment
Authors: Krouskop T. A. , Trono Ruben , Adamski A. J. 
Published: December 2004

AbstractThe attachment of a prosthesis directly to the part of the skeleton remaining after an amputation offers many improvements over coupling schemes used in conventional prostheses. However, the stresses induced in the bone by the macrostructure of the attached prosthetic device must first be understood because they are a significant consideration in the design of a successful direct skeletal attachment (DSA) system.This investigation utilizes the finite element method of analysis to structurally model some possible DSA systems. Static stress‐response models for an above‐the‐knee human femoral amputation are formulated to investigate the effect of variations in pylon macrostructure on system performance. The models approximate the initial stages of support following the insertion of a pylon into the medullary cavity of the bone and are also used to assess the bond strengths that must be developed between the bone and pylon for a “no–slip” condition to hold at their interface.The analyses indicate that either a shaped, marrow cavity‐fit pylon or four 135 degree wedges with a complementary pylon are favorable geometries for a DSA system. The stress levels caused by these two geometries are on the order of 20% of the axial compressive strength of cortical bone. For each, local stress levels at the bone–biomaterial interface remain the critical parameters for investigation.
Dead or alive: The problem of in vitro tissue mechanics
Authors: Black Jonathan 
Published: December 2004

AbstractExtensive studies have been made of the biomechanical properties of tissues in vitro. The majority of experiments demonstrate a “preconditioning” effect. This effect is associated with the differences between in vivo and in vitro conditions. Failure to utilize initial or isochronal data may lead to erroneous conclusions. Objective criteria would permit comparison between experiments.
Tissue response to implanted polymers: The significance of sample shape
Authors: Matlaga Barbara F. , Yasenchak Lewis P. , Salthouse Thomas N. 
Published: December 2004

AbstractStudies were designed to demonstrate the need for standardization of shape of samples used as implants to evaluate histotoxicity of polymer materials. Six medical‐grade polymers (polypropylene, polyethylene, polyurethane, silicone rubber, poly(vinyl chloride), and Teflon) were extruded as rods with circular‐, triangular‐, and pentagonal‐shaped crosss ections, and were implanted in rat gluteal muscles for 14 days. Evaluation of the tissue response was assessed by quantitating cellular lysosomal acid phosphatase enzyme activity by using microspectrophotometry. All triangular‐shaped implants showed the highest enzyme activity and cellular response; pentagon shapes showed less, and circular rods showed the lowest activity. The results demonstrate the need for standard sample shape for valid comparative studies of tissue response to implanted polymers.
The interaction of macromolecular solutions with macromolecular monolayers adsorbed on a hydrophobic surface
Authors: Fromageot Henri P. M. , Groves James N. , Sears Alan R. , Brown John F. 
Published: December 2004

AbstractIn order to elucidate the general patterns of intermacromolecular surface interactions that may be involved in hemocompatibility phenomena, monolayers of representative macromolecules on an octadecylsilylated glass surface were exposed to solutions of other macromolecules, and the changes in interfacial composition were characterized by zeta potential–pH titration curves, as measured by alternating flow streaming current analysis and, in some cases, by radiotracer labeling. Experiments with poly(vinylpyrrolidone) (PVP), a blood‐compatible linear polymer; bovine serum albumin (BSA), a representative serum protein; whole human serum (HS), a complex mixture of proteins; and erythrocyte surface glycoprotein (GP), an extended‐chain macromolecular amphiphile, showed the following: (1) Penetration of the original monolayer occured within 24 hr in 9 of the 12 possible cases; it did not occur for BSA or HS monolayers exposed to PVP, and probably not for PVP exposed to GP. (2) In all cases, penetration was accompanied by no more than partial displacement of the original monolayer, thereby generating a mixed monolayer. Each of the six possible binary mixed monolayers could be obtained by at least one of the two possible mixing sequences. (3) In the three binary systems containing BSA, the formation of the mixed monolayer could be related to increased adsorption in the two‐component system. (4) The two components of the mixed monolayers were not equally distributed across their thicknesses: thus, the outer surfaces of the PVP–BSA and (at neutral pH) the PVP–HS mixed monolayers contained only PVP; that of the BSA–HS mixtures only HS. In the PVP–HS, and probably the GP–BSA and GP–HS mixed monolayers, the composition of the outer surface appeared pH‐dependent. The resultant zeta potential versus pH profiles in the latter two cases resembled those of intact blood cells.The results suggest that neither the compact monolayers of globular proteins nor the diffuse monolayers of randomly coiled water‐soluble polymers can, by their prior adsorption on a synthetic surface, prevent the subsequent adsorption of other globular macromolecules. It is possible that the randomly coiled polymers may impede the adhesion of platelets to the substrate since the results indicate that the adsorption of such polymers causes a displacement of the shear plane.
Bone ingrowth into dynamically loaded porous‐coated intramedullary nails
Authors: Collier J. P. , Colligan G. A. , Brown S. A. 
Published: December 2004

AbstractResearch to determine whether porous‐coated Vitallium intramedullary rods could be used to bridge segmental defects in long bones was performed using rabbit tibias as a suitable model for human bone growth. One‐centimeter segments of the midshaft of tibias of mature rabbits were removed surgically and replaced with equal‐sized segments of Silastic tubing to maintain leg length. A coated rod was inserted through the proximal tibial segment, through the tubing, and into the distal bone segment. The legs were taken out of plaster at 3 weeks, and x‐rays were taken periodically until sacrifice.At sacrifice, 30 weeks postoperatively, the mechanical properties of both tibias from each rabbit were measured destructively in a torsional testing machine. The load at failure of the tibia with the segmental defect averaged 90% of the contralateral control tibia. Rod pullout data and electron‐probe x‐ray microanalysis indicated that a substantial rod–endosteal bone bond existed due to ingrowth into the porous coating. The torsional data may have been somewhat obscured by the presence of a bony callus which grew over the Silastic tubing and bridged the segmental defect exosteally in every case.
Animal studies on bone ingrowth kinetics of ceramic material under dynamic stress
Authors: Dörre E. , Geduldig D. , Happel M. , Lade R. , Prüssner P. , Willert H.‐G. , Zichner L. 
Published: December 2004

AbstractTwo of the primary problems of implants in use today result from the materials used in their construction (metal and polyethylene) and from the necessary additional fixation with bone cement. In order to alleviate these well known difficulties, we studied ceramic material (99.7% Al2O3 with 0.25% MgO) which exhibits several advantages in these areas, but has a diminished bending stregth.To take advantage of the ceramic material, we tested a cement‐free implantation which should allow unhindered growth of bone tissue to or into the material. In particular, the interface relationship under load bearing was investigated.The course of the tissue differentiation and ingrowth on the surface of the ceramic implants under dynamic stress, was studied by a specifically designed distance‐spacer. These were tested on the femur of foxhounds and sheep, as well as by use of temporary immobilization. Histological investigations in intervals of 4 weeks showed the course of the development of the interface tissue. After removal of the binding materials, the behavior of the implant support is studied in 4‐week intervals with free load bearing. Radiological and histological development studies are shown.The results we obtained implicate the use of ceramic implants. But the application in humans still seems to be problematic, as there is a need for designs which are loaded by pressure only.
Chemical and mechanical behavior of bioglass‐coated alumina
Authors: Greenspan D. C. , Hench L. L. 
Published: December 2004

AbstractProcedures for applying nonporous bioglass coatings to fully dense, high‐purity alumina are described. By altering firing temperatures and number of coatings, the rate of surface reactivity of the coated alumina can be varied. Bonding of bioglass‐coated alumina to rat bones is reported as early as three weeks.
Biomechanically induced tissue reactions after Al2O3–ceramic hip joint replacement. Experimental and early clinical results
Authors: Griss P. , Silber R. , Merkle B. , Haehner K. , Heimke G. , Krempien B. 
Published: December 2004

AbstractA biomechanical concept of interface maturation around cement‐free implanted alumina–ceramic hip endoprostheses in sheep is explained. Provided there is rigid primary stability of the implant within the bone bed, hard tissue formation along the support areas of the implant is mainly dependent on implant shape and main local stress direction. Three subsequent phases of interface maturation can be distinguished, finally resulting in firm fixation of the implant by mechanical interlocking of supporting bone and ceramic.A new composite alumina–metal hip endoprosthesis for partial cement‐free implantation (cup) is presented. The technique, postoperative care, and encouraging early results in 5 patients are demonstrated. A new ceramic femoral component for cement‐free implantation is proposed.
Postyield behavior of subchondral trabecular bone
Authors: Hayes W. C. , Carter D. R. 
Published: December 2004

AbstractCylindrical specimens of bovine subchondral trabecular bone were tested to uniaxial compressive strain levels of 75% to study energy absorption during pore collapse. Stress–strain curves were characterized by macroscopic yield at about 8% strain followed by a significant horizontal pore collapse regime. Energy absorption occurred largely in this postyield regime. Yield strength and energy absorption capacity were found to increase linearly with specimen apparent density. Microstructural analysis of the deformed specimens verified that the mechanism for energy absorption was primarily fracture and buckling of trabeculae. The results suggest that during fracture, the collapse of trabecular bone (and the consequent absorption of energy) serves to attenuate stresses transmitted through the skeleton and thus protect vital structures such as the brain.
Biocompatibility studies on surgical‐grade titanium‐, cobalt‐, and iron‐base alloys
Authors: Lemons J. E. , Niemann K. M. W. , Weiss A. B. 
Published: December 2004

AbstractAn animal model system for the investigation of the influence of in vivo‐ produced metallic corrosion products upon tissues has been developed. Externally applied electrical stimulation produces the corrosion over a short period of time, and a poststimulation period is allowed for tissue stabilization.Tissue reaction adjacent to the metallic alloys shows fibrous tissue capsules and metallic corrosion product contamination.These preliminary studies show that this animal model and methodology may provide a technique for investigating long‐term tissue biomaterial interactions and the influence of iron (316L), cobalt (Vitallium), and titanium (Tivanium) alloy corrosion products upon the susceptibility of tissues to various biocompatibility challenges.