bluuebunny/crossref_metadata_2025_split huggingface dataset:
Osteoinduction within porous polysulfone implants at extraosseous sites using demineralized allogeneic bone matrix
Authors: Vandersteenhoven J. J. , Spector M. 
Published: December 2004

AbstractThe objective of this study was to determine if bone induction could occur in implants of porous polysulfone (PPSF) impregnated with particles of demineralized allogeneic bone matrix (DABM). DABM–PPSF composites were fabricated by inserting DABM particles into PPSF specimens. The porous implants were produced by sintering polysulfone particles (850–1180 μm in diameter). DABM particles were prepared by demineralizing rat cortical bone in 0.6N HCl at 4°C for 18–24 h. A composite DABM–PPSF specimen and three “controls” were implanted subcutaneously at abdominal sites in 30 adult Sprague–Dawley rats. The three controls were whole DABM (4 × 4 × 1 mm), particulate DABM (1 × 1 × 1 mm), and porous polysulfone (5 × 5 × 1 mm). Microradiographic and histological evaluation of DABM–PPSF composites revealed chondrogenesis within the pores of the specimens at 10 days, followed by ossification and fatty marrow production at 21 and 43 days. This histological sequence was similar to that seen with DABM controls. The tissue response to porous polysulfone did not prevent the osteoinductive process. These results suggest that an osteoinductive material such as DABM may be useful in augmenting the implantation of porous implants at osseous sites in which the potential for bone regeneration is limited.
Cement strain measurement surrounding loose and well‐fixed femoral component stems
Authors: Crowninshield Roy D. , Tolbert James R. 
Published: December 2004

AbstractStrain measurement within the cement surrounding stemmed total hip femoral components was accomplished using PMMA encapsulated and embedded strain gauges. Cement strain measurement associated with a well‐bonded stem–cement interface and an unbonded stem–cement interface (i.e., loose prosthesis) was performed. The presence of a stem–cement bond was found to reduce proximal cement strain magnitudes while having little effect on distal cement strain magnitudes. The assurance of a stem–cement bond on only the proximal third of the interface was found to have an effect similar to that of a complete stem–cement bond. The results of this experimental investigation confirm the theoretical prediction that the stem–cement bond is important in maintaining the integrity of the cement mantle surrounding a stemmed femoral component.
Retrieval analysis of total knee prostheses: A method and its application to 48 total condylar prostheses
Authors: Hood Roger W. , Wright Timothy M. , Burstein Albert H. 
Published: December 2004

AbstractA technique for the classification and quantification of damage in retrieved total knee prostheses is presented and applied to the examination of 48 removed total condylar‐type knee replacements. The technique involves inspection of all metallic and polyethylene components for evidence of gross deformation, fracture, and damage to articulating surfaces. A grading system was developed to quantitate surface damage on polyethylene components. Results of the examinations are combined with patient variables (weight, activity level, radiographic findings, time of implantation, and results of histology performed on surrounding tissue) to determine correlations between clinical variables and the mechanical damage experienced by the prostheses. For the 48 total condylar‐type prostheses, significant positive correlations were found for the surface damage correlated with the patient's weight and the time the prosthesis was implanted.
Macroporous hydrogel membranes for a hybrid artificial pancreas. II. Biocompatibility
Authors: Klomp Gregory F. , Hashiguchi Hiroshi , Ursell Philip C. , Takeda Yoshi , Taguchi Tadahiro , Dobelle William H. 
Published: December 2004

AbstractA histological evaluation of the biocompatibility of a new porous hydrogel membrane made of 2‐hydroxyethyl methacrylate (2‐HEMA) was performed. Isolated membranes and diffusion chambers made of this material and filled with rabbit pancreas were implanted in diabetic rats for periods of up to 8 1/2 months. Histologic evaluation showed that this polymer elicits minimal tissue reaction within the first 7 weeks but some increase in granulation tissue and fibrosis thereafter. A component of this tissue reaction is neovascularization, and many blood vessels were noted immediately adjacent to the membrane's surface. Calcification of the membrane was also progressive but could be minimized by formulations resulting in the incorporation of acid groups throughout the hydrogel and on its surface. Diffusion chambers made of this new material show promise for use in a “hybrid” artificial pancreas for the treatment of diabetes.
Creep of conventional and microfilled dental composites
Authors: Papadogianis Yannis , Boyer Daniel B. , Lakes Roderic S. 
Published: December 2004

AbstractThe creep of microspecimens of two conventional and two microfilled composites was studied using a torsional creep apparatus. Small stresses below the materials' proportional limits were maintained for 3 h and recovery was monitored for 30 h. Creep curves were obtained at 21.5,37, and 50°C, and three torque levels. The composites exhibited linear viscoelastic behavior at low deformations. The magnitude of creep depended on the amount and type of resin in the composites. The materials did not recover their original shape after 30 h after the stress was removed. No transitions were observed in the temperature range employed. The shear moduli decreased with temperature and are in reasonable agreement with literature values obtained with other tests.
Long‐term compressive creep deformation and damage in acrylic bone cements
Authors: Chwirut Daniel J. 
Published: December 2004

AbstractCompressive creep tests were performed on five commercially available acrylic bone cements under conditions simulating in vivo usage. Measured creep strains are quite large, generally exceeding elastic strains. Large variations in creep response were noted among the various cements, with a carbon‐reinforced cement by far the most resistant to creep. The empirical model ϵ = a exp(bσ)tn was found to predict creep strains within about 10% of the measured values. Microscopic examination of some specimens after testing revealed significant cracking, resulting from long‐term loading, that could be a contributing cause of time‐dependent failure.
The glutaraldehyde‐stabilized porcine aortic valve xenograft. I. Tensile viscoelastic properties of the fresh leaflet material
Authors: Lee J. Michael , Courtman David W. , Boughner Derek R. 
Published: December 2004

AbstractThe tensile viscoelastic properties of radial and circumferential strips of fresh porcine aortic valve leaflets have been examined and compared with the fiber architecture of the leaflets as seen in the scannng electron microscope. The leaflet material showed nonlinear viscoelasticity, largely independent of strain rate, and dependent on the degree of preconditioning by cyclic loading. Preconditioning to a stable stress‐strain response could only be accomplished on 1‐cm‐long strips above a minimum width of 4 mm (circumferential) and 6 mm (radial). Preconditioning yielded a more elastic and extensible material with reduced hysteresis. The leaflets were markedly anisotropic. Circumferential strips were up to 8 times stronger and stiffer than radial strips, and displayed greater stress relaxation and less creep. The circumferential mechanical properties were due to well‐aligned circumferential collagen bundles reinforcing the composite structure, while radial properties were due to a more random collagenous support throughout the leaflet. Despite the presence of a septal shelf on the right coronary leaflet, no mechanical differences could be discerned between leaflets.
On the true wear rate of ultrahigh molecular weight polyethylene in the total knee prosthesis
Authors: Rose Robert M. , Ries Michael D. , Paul Igor L. , Crugnola Aldo M. , Ellis Edward 
Published: December 2004

AbstractThe objective of this investigation was to assess the magnitude of the true wear of the polyethylene components of several total knee replacements. Five different prostheses were tested by total joint simulation for the equivalent of 1 month of use. The true wear rates of the tibial components were measured by quantitative recovery of the polyethylene debris. After testing, the tibial components were examined in the scanning electron microscope, and the molecular weight distributions were analyzed. The wear rates were found to range from 0.3 to 1.8 mg per month. The soluble fraction molecular weights ranged from 179,000 to 393,000 with 53–78% soluble. The wear rates, significantly larger than those observed for total hip prostheses, are dominated by the high contact stresses in these prostheses. The wear results in dimensional changes, which are of the same order of magnitude as those due to creep. The debris had two components: fine fibrous particles, found in all cases, and coarse granules, found when the wear rate is relatively high. Evidence for fatigue cracking was found at the surfaces of the tibial component with the highest wear rate. This behavior is consistent with other investigations of the material itself and indicates that continuous deterioration of the polyethylene should be expected in this class of prosthesis.
The effect of humoral components on the cellular response to textured and nontextured PTFE
Authors: Korman N. J. , Sudilovsky O. , Gibbons D. F. 
Published: December 2004

AbstractThe investigation was undertaken to determine the role that humoral components play in the biological response to ion beam textured and smooth PTFE. It was found that exudates obtained from smooth PTFE implants contained factors capable of promoting the attachment and growth of cells in vitro. Exudates obtained from textured PTFE contained significantly more growth promoting activity at 2 days after implantation and significantly more attachment promoting activity at 2 and 7 days after implantation than corresponding exudates obtained from smooth PTFE. The underlying reasons for the temporal nature of these results are not known, but cellular mechanisms were proposed to explain the observed differences. In order to examine protein adsorption to implants in vivo, a technique was developed utilizing the Selye air pocket and electrocautery to minimize cell adhesion to the implants. The results demonstrated the dynamic quality of protein adsorption to surfaces and indicated that the nature of protein exchange at the material surface differed between textured and smooth PTFE for the first 30 min post‐implantation. Both albumin and fibrinogen were identified on textured and smooth surfaces, but fibronectin was not identified on any of the surfaces.
Heparin immobilization onto segmented polyurethaneurea surfaces—effect of hydrophilic spacers
Authors: Park Ki Dong , Okano Teruo , Nojiri Chisato , Kim Sung Wan 
Published: December 2004

AbstractHeparin was immobilized onto segmented polyurethane‐urea surfaces (Biomer) using hydrophilic poly(ethylene oxide) spacers of different chain lengths. The use of the hydrophilic spacer, poly(ethylene oxide), reduces protein adsorption and subsequent platelet adhesion on the surface. In addition, the bioactivity of the immobilized heparin is enhanced by the incorporation of these spacers. Immobilized heparin bioactivity is shown to be a function of PEO spacer length. Use of hydrophilic PEO spacers demonstrates that immobilized heparin's bioactivity is consistently higher than that of the C6 alkyl spacer, but heparin‐immobilized surfaces demonstrate no chain length effect on platelet adhesion, even though they show less platelet adhesion compared to Biomer controls. In the case of PEO‐grafted surfaces, platelet adhesion is decreased compared to Biomer controls, and C6 alkyl spacer‐grafted surfaces, and exhibits a minimum at PEO 1000. In ex vivo A–A shunt experiments under low flow and low shear conditions, all heparinized surfaces exhibit significant prolongation of occlusion times compared to Biomer controls, indicating an ability of immobilized heparin to inhibit thrombosis in whole blood.
In vitro synergistic, antagonistic, and duration of exposure effects of metal cations on eukaryotic cells
Authors: Wataha J. C. , Hanks C. T. , Craig R. G. 
Published: December 2004

AbstractEffects of duration of exposure of single metal cations (Ag+1, Cd+2, Cu+2, Ga+3, Ni+2, and Zn+2) on 3H‐thymidine (3H‐Tdr) incorporation and 3‐[4,5‐dimethylthiazol‐2yl‐]‐2,5‐diphenyl tetrazolium bromide‐formazan (MTT‐f) production in cultured murine fibroblasts (Balb/c 3T3) were investigated, and the synergistic and antagonistic effects of two metal cations applied simultaneously to the fibroblasts were assessed. The effects of duration of exposure were quantified using TC50 values (concentration of an element required to cause 50% toxicity compared with controls) measured after 24, 48, or 72 h. Using MTT‐f production, Cd+2, Cu+2, Ga+3, and Ni+2 showed significantly lower TC50 values with increasing time of exposure, whereas the TC50 values for Ag+1 and Zn+2 remained constant. The TC50 values using 3H‐Tdr incorporation exhibited a similar pattern with time of exposure, but the effects were less pronounced. The TC50 values for 3H‐Tdr and MTT‐f tended to equalize at 72 h. All combinations of cations tested (Ag‐Cu, Ag‐Zn, Ag‐Ni, Cu‐Zn, Cu‐Ni, Cu‐Ni, Ga‐Ni, and Cu‐Cd) exhibited synergistic and antagonistic effects were not necessarily mutually exclusive in the same system. © 1992 John Wiley & Sons, Inc.
Tissue compatibility of collagen‐silicone composites in a rat subcutaneous model
Authors: Wallace Donald G. , Rosenblatt Joel , Ksander G. A. 
Published: December 2004

AbstractCollagen‐silicone composites were fabricated and tested for biocompatibility by subcutaneous implantation in rats. The silicone component consisted of addition cure or condensation cure sheets. The collagen component was either (a) a sponge layer 2 mm thick, (b) a thin film 12‐20 μm thick, or (c) residual collagen bonded to or incorporated in the silicone rubber. Collagen sponges were mechanically bonded to silicone sheets, and collagen thin films and residual collagen were physically and chemically attached to epoxyderivatized silicone sheets. Analysis of implanted samples showed that reduced capsule formation occurred around collagen spongesilicone, compared to control silicone sheets. Only where the underlying silicone sheet, or interpenetrating silicone, was exposed to the tissue, did limited capsule formation occur. In contrast, thin capsule developed completely around silicone coated with a thin collagen film and around silicone bonded to residual collagen. Sponge‐silicone composites and control silicone sheets were free of acute and chronic inflammation, except for occasional foreign body giant cells in sponge adjacent to silicone. Silicone coated with micron‐thick collagen films exhibited some inflammation, but residual collagen‐silicone did not. This study suggests that, to prevent capsule formation, a collagen coat must be of minimum thickness and surface coverage sufficient to prevent any contact between silicone and tissue. © 1992 John Wiley & Sons, Inc.
Hydroxyapatite coatings on Ti produced by hot isostatic pressing
Authors: Herø Håkon , Wie Henrik , Jørgensen Randi B. , Ruyter I. Eystein 
Published: December 2004

AbstractPlasma spraying is a technique currently used in the production of HA‐coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long‐term interface strength has been questioned in particular. The aim of the present work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850°C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the Ti substrate. The Ti specimens were then cold‐pressed, enclosed by a protective Pt foil, and encapsulated in an evacuated glass ampulla. Subsequent to HIP, the glass and the Pt foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was measured to be > 62 MPa, which is considered to be satisfactory. The structure of the coating was checked by X‐ray diffraction and IR spectroscopy, and was found to correspond to that of HA. Some cracks were observed in the coating running predominantly vertical to the surface. Whether these are acceptable has to be verified by in vivo experiments. © 1994 John Wiley & Sons, Inc.
Factor XII fragment and kallikrein generation in plasma during incubation with biomaterials
Authors: van der Kamp K. W. H. J. , van Oeveren W. 
Published: December 2004

AbstractBlood biocompatibility of medical devices is in many ways dependent on surface characteristics and biochemical blood material interactions. In this study, the contact system, in which the activation of factor XII and plasma kallikrein is included, is highlighted. This article describes a simple chromogenic assay to determine the Hageman Factor fragment (HFf, or factor XIIf) and kallikrein activity in vitro. The assay is based on conversion of Z‐Lys‐Phe‐Arg‐pNA. 2HCl to which human factor XIIf and kallikrein appeared to have a high affinity. To discriminate between the serine proteases factor XIIf and kallikrein to cleave this substrate, aprotinin was added to one of two complementary samples. In this in vitro study, standardized disks from glass, high‐density polyethylene (HDPE), polytetrafluoro ethylene (PTFE), and polydimethyl siloxane (PDMS) were studied for their capacity to generate factor XIIf and kallikrein in plasma. Kaolin was used as positive control. On glass disks the highest and on HDPE the lowest generation of factor XIIf and kallikrein were found, both with a ratio of 1 : 1. On PDMS and on PTFE disks protease activities were intermediate, but with a factor XIIf and kallikrein activity ratio of 1 : 2 and 1 : 4, respectively. Apparently because of the hydrophobic surface character of PDMS and PTFE, these surfaces absorb or fail to produce the factor XIIf. This assay appeared to be discriminative even for materials that are considered mild activators of the contact system and can therefore be used as a standard method to qualify biomaterials. NOTE: Factor XIIf(mol wt. 28,000) is designated in the literature as HFf, β‐factor XIIa, or factor XIILMW and factor XIIa (mol wt. 80,000) as HFa, factor XIIaHMW, or α‐factor XIIa. To avoid the unfashionable use of β‐factor XIIa or α‐factor XIIa, we chose in this study the use of factor XIIf and factor XIIa, according to the article by R. A. Pixley et al., Blood, 66, 198–300 (1985). © 1994 John Wiley & Sons, Inc.
Inhibition of platelet spreading from plasma onto glass by an adsorbed layer of a novel fluorescent‐labeled poly(ethylene oxide)/poly(butylene oxide) block copolymer: Characteristics of the exclusion zone probed by means of polystyrene beads and macromolecules
Authors: Gingell D. , Owens N. 
Published: December 2004

AbstractWe have investigated the anti‐adhesive properties of a newly synthesized fluorescent triblock copolymer containing poly(ethylene oxide). This adsorbs from aqueous solution onto glass that has been rendered hydrophobic. When the polymer‐treated surface was exposed to human platelet‐rich plasma (PRP) or whole blood at 37°C, platelet adhesion and spreading were prevented. Avid adhesion and rapid platelet spreading occurred along tracks scraped in the adsorbed polymer coating, as seen by video‐enhanced interference reflection microscopy. Leukocytes from whole blood are eventually able to adhere to the polymer‐treated surface and were seen to remove labeled polymer from their vicinity and accumulate it at the cell body. Interferometry using polystyrene spheres showed that they do not adhere to polymer‐coated glass and are unable to approach closer than 70–95 nm. On scraped tracks, beads make molecular contacts with the glass. Because the fully extended solvated (EO)400 arms may extend up to 100 nm from the glass, this suggests that the polymer forms a monolayer with the hydrophilic arms projecting into the water, whereas the hydrophobic (BO)55 segment binds the molecule to the hydrophobic surface. Another tribloc copolymer with shorter hydrophilic arms allows particles to approach more closely. © 1994 John Wiley & Sons, Inc.
Long‐term in vivo and in vivo aging of a zirconia ceramic used in orthopaedy
Authors: Cales B. , Stefani Y. , Lilley E. 
Published: December 2004

AbstractA detailed study of a commercial zirconia (Y‐TZP) aged at 37°C held in Ringer's solution or transplanted in animals or humans is reported. No degradation in strength was found for MOR bars or for hip joint heads subjected to stresses caused by pressing titanium alloy trunnions into the head tapers with loads up to 30 kN. Polished specimens also showed no increase in the monoclinic phase percentage upon aging for 1 year. Small specimens transplanted in animals experience no change in the micro‐indentation KIC toughness value, suggesting no degradation. Zirconia heads recovered after 2 years of human implantation showed no loss of strength. The difference between the excellent performances of this ceramic presented here and other studies can be accounted by the microstructural design and quality of the zirconia. © 1994 John Wiley & Sons, Inc.
An ab initio study of the influence of substituents and intramolecular hydrogen bonding on the carbonyl bond length and stretching force constant. I. Monosubstituted carbonyl compounds
Authors: Bock Charles W. , Trachtman Mendel , George Philip 
Published: December 2004

AbstractThe CO bond length and fCO,CO, the corresponding harmonic stretching force constant, are calculated ab initio using the 4‐31G basis set (augmented by polarization functions on the sulfur and chlorine) with full geometry optimization for the monosubstituted carbonyl compounds RCHO, where R = H, CHO, CHCH2, CO2H, CHCHOH, OH, OC(O)OH, OOH, SH, Li, F, Cl, and NH2. Straight‐line relationships are found in plots of ln[fCO,CO] vs. ln[rCO] for the series of compounds in which carbon atoms and oxygen atoms are bonded directly to the carbonyl carbon, in accordance with the empirical expression f = C′/rn. The slopes and intercepts give n = 7.62 and 6.47, C′ = 62.6 and 48.6, for the lines with carbon and oxygen as the atom bonded directly to the carbonyl carbon, respectively. The point for formaldehyde lies very close to the C line, whereas the points for SH, Li, F, Cl, and NH2 lie closer to the O line.