bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics supramolecular structure and equilibrium properties of fibrinogen adsorption at liquid–solid interfaces
Authors: Nygren Hȧkan , Stenberg Manne , Karlsson Christin 
Published: December 2004

AbstractAdsorption of fibrinogen onto hydrophobic and hydrophilic quartz surfaces was studied by ellipsometry and transmission electron microscopy (TEM) of negatively stained proteins. The initial adsorption at the hydrophobic surface, measured by ellipsometry, can be described by an apparent forward rate constant kl of 2 × 104 M−1 s−1. This constant was time‐dependent and is therefore considered as a rate coefficient. The apparent forward rate coefficient of adsorption to a hydrophilic surface was both time‐dependent and concentration‐dependent, indicating a history‐dependent process of adsorption. Plateau levels of adsorption were concentration‐dependent and lower at the hydrophilic quartzsur face (1.2 pmol/cm2) than at the hydrophobic surface (1.8 pmol/cm2). These surface concentrations correspond to rather tight‐packed monolayers of molecules adsorbed end‐on. The initial desorption can be described by a first order rate constant (k−1≈10−4s−1), down to 80‐90% of the initial surface concentration. The dissociation rate then decreased (k−1 ≈10−6 s−1) resulting in an apparently stable level of adsorbed protein. Slow changes of the binding strength of adsorbed proteins was seen during 24–72 h adsorption time. Deviations from an ideal equilibrium isotherm were seen both in the time dependence and as concavities in a Scatchard plot, suggesting intermolecular cooperativity. At low bulk concentrations a heterogeneous distribution of fibrinogen molecules was found at the surface below monolayer coverage. The supramolecular structure was characterized by the formation of end‐to‐end dimers and trimers laying down at the surface. At higher surface concentration adsorbed molecules showed polycrystalline structure with repeated nearest neighbordistances at 16 nm. The distribution of adsorbed fibrinogen molecules indicates that surface‐adsorbed fibrinogen may form a two‐phase system, containing significant amounts of water. The atypical kinetics and concentration dependence of fibrinogen adsorption may thus be due to properties of a two‐dimensional phase separation from a three‐dimensional liquid bulk.
Enhanced ingrowth of porous‐coated CoCr implants plasma‐sprayed with tricalcium phosphate
Authors: Chae John C. , Collier John P. , Mayor Michael B. , Surprenant Victor A. , Dauphinais Leo A. 
Published: December 2004

AbstractTricalcium phosphate (TCP) is an osteoconductive bioceramic which, when applied to a porous‐coated prosthesis, may enhance osseous ingrowth and mechanical stability. TCP plasma‐sprayed and unsprayed porous‐coated tibial intramedullary rods were bilaterally implanted in seven adult rabbits. All rabbits were killed at 12 weeks. Pull‐out tests were performed on 4 rabbits while all were evaluated histologically for osseous response and adverse tissue reaction. TCP‐sprayed implants showed significantly greater osseous ingrowth in comparison to unsprayed implants. Neither implant type exhibited adverse tissue reactions. Average pull‐out strengths were 69 lb for treated rods and 72 lb for controls (p > 0.05); quality of fit for all pull‐out specimens except one was deemed poor. We conclude that plasmasprayed TCP enhances osseous ingrowth into porous‐coated devices. However, our data further suggest that enhanced ingrowth may not always lead to enhanced fixation.
In vitrocorrosion fatigue of 316L cold worked stainless steel
Authors: Taira Masayuki , Lautenschlager Eugene P. 
Published: December 2004

AbstractThe corrosion resistance of 316L cold worked stainless steel depends upon its thin protective oxide layer; and if this is partially broken down, corrosion resistance depends upon its tendency for repassivation. Since the intended function of stainless‐steel implants is to sustain musculoskeletal forces, research toward the stability of the oxide film during dynamic loading in simulated bodylike fluids is warranted. A pilot corrosion fatigue study was, therefore, performed on uniaxial tension fatigue specimens cycled to various maximum stress levels near their yield point while immersed in 37°C isotonic saline solution, and combined with the electrochemical insult of (a) imparting an 800 mV vs. SCE anodic potential for 20 s to stimulate local film breakdown, and then (b) returning to a constant 200 mV vs. SCE anodic potential and maintaining that potential during cyclic loading until the specimens broke in two. During the anodic polarization by continuously monitoring the current it was possible to (a) observe the repassivation and corrosion behavior following stimulation, and (b) detect crack initiation, crack propagation and failure onset. The combined effects of accelerated corrosion and mechanical fatiguing disturbed the repassivation tendency and reduced the crack initiation times and the fatigue lives as compared to air and saline controls. As the maximum cyclic load levels were increased, the fatigue lives were further foreshortened.
Protein interaction with tantalum: Changes with oxide layer and hydroxyapatite at the interface
Authors: Sharma Chandra P. , Paul Willi 
Published: December 2004

AbstractFor metallic implants the surface nature is extremely important because blood and tissue interactions with metal depend upon it. Protein adsorption is the initial reaction that takes place when an implant comes in contact with blood or tissue. We attempted to coat different thicknesses of oxide layers and hydroxyapatite on tantalum and examined the changes in water contact angle and adsorption of albumin and fibrinogen. Protein adsorption studies were performed with 125I‐labeled proteins. A decrease in water contact angle was observed as the oxide layer thickness of tantalum increased. Fibrinogen adsorption increased on oxide layer coated and hydroxyapatite coated surfaces, compared to bare tantalum. © 1992 John Wiley & Sons, Inc.
Prevention of tissue calcification on bioprosthetic heart valve by using epoxy compounds: A study of calcification tests in vitro and in vivo
Authors: Tingfei Xi , Jiazhen Ma , Wenhua Tian , Xuehui Lei , Shuhui Long , Baoshu Xi 
Published: December 2004

AbstractCalcification is the principal cause of the clinical failures of the bioprosthetic heart valves fabricated from glutaraldehyde pretreated porcine aortic valves or bovine pericardium. In this paper, we compared the calcification on various types of bovine pericardiums pretreated with two hydrophilic epoxy compounds adding GA post‐treatment (EP 1 and EP 2), glutaraldehyde (GA)‐ and nontreated pericardium (Fresh), respectively, by in vitro and in vivo tests. Significant decrease of calcification was found by pretreatment with both epoxy compounds rather than with glutaraldehyde : 0.250 ± 0.001 (Fresh), 0.276 ± 0.058 (EP l), 0.302 ± 0.071 (EP 2), and 0.478 ± 0.172 (GA) μg (Ca)/mg (dried tissue), respectively, after 20 days dipping in a simulating serum solution in vitro; 115.13 ± 60.11 (Fresh), 129.84 ± 51.08 (EP 1), 167.39 ± 20.81 (EP 2), and 205.19 ± 16.86 (GA) pg/mg, respectively, after 3 months subcutaneous implantation i n rabbits. The in uifro method for evaluating calcification designed by us gave the similar order among four samples with that obtained by in uiuo test. Because the bovine pericardium pretreated with the epoxy compounds adding GA post treatment possesses the greater tenacity than that pretreated only with epoxy compounds or GA, meanwhile the calcification is also significantly decreased with this pretreatment, it may be expected that the bovine pericardium with this pretreatment will have the greater anticalcification and durability in dynamic stress. © 1992 John Wiley & Sons, Inc.
The effect of calcium phosphate ceramic composition and structure on in vitro behavior. II. Precipitation
Authors: Radin S. R. , Ducheyne P. 
Published: December 2004

AbstractThe formation of a biologically equivalent carbonatecontaining apatite on the surface of synthetic calcium phosphate ceramics (CPC) may be an important step leading to bonding with bone. Reactions of several single phases CPCs upon immersion into a simulated physiologic solution (SPS) with an electrolyte composition of human plasma were determined. The CPCs covered a wide range of solution stabilities from low‐soluble hydroxyapatites (HA) to metastable tricalcium phosphates (TCP) and tetracalcium phosphate (TTCP). Changes in chemical composition of SPS and infrared spectral features after CPC immersion were analyzed. New phase formation was observed on all the CPCs. However, kinetics, compositions, and structures of the new phases were significantly different. The studied CPCs can be characterized by the time to new phase formation in vitro; the minimum time for measurable precipitate formation was found to increase in the order: not‐well‐crystallized HAs < well‐crystallized HAs < α‐TCP, TTCP < β‐TCP. Among the CPCs only not‐well‐crystallized HAs led to immediate new phase formation. The metastable CPCs, β‐TCP, α‐TCP, and TTCP required an induction time during which dissolution occurred. β‐TCP showed the longest induction time and the lowest lattice ion uptake rate of all the CPCs tested. Only the not‐well‐crystallized HAs elicited immediate formation of carbonated HA. The well‐crystallized HAs and β‐TCP did not elicit carbonated apatite formation within the time frame of the experiment. Instead, intermediate phases were formed. On α‐TCP amorphous calcium phosphate (ACP) with a relatively low carbonate content was formed. TTCP was found to transform extensively to poorly crystallized carbonated apatite after 2 days of immersion. © 1993 John Wiley & Sons, Inc.
Extensive porosity at the cement–femoral prosthesis interface: A preliminary study
Authors: James S. P. , Schmalzried T. P. , McGarry F. J. , Harris W. H. 
Published: December 2004

AbstractThis study is the first description of the extensive porosity which is preferentially located at the cement‐prosthesis interface of cemented femoral components of total hip replacements. The observation is important because the interfacial porosity may decrease the strength of the cement‐femoral prosthesis interface and jeopardize the mechanical integrity of the cement mantle. We examined the cement‐metal interfaces from a multiplicity of in vivo and in vitro specimens using both optical and scanning electron microscopy. These samples included several stem designs, implants made from either Co‐Cr or Ti alloy, implants made with a variety of surface finishes and both centrifuged and uncentrifuged cement. All in vivo and in vitro samples had marked porosity in the cement focally concentrated at the cement‐metal interface. The amount of porosity at the interface greatly exceeded the amount of general porosity found throughout the bulk cement. Centrifuging did not affect the interfacial porosity, and neither did alloy nor surface finish. The presence of these pores may be expoained by the rheological characteristics of the cement. © 1993 John Wiley & Sons, Inc.
Bacterial adhesion to poly(HEMA)‐based hydrogels
Authors: Cook Alonzo D. , Sagers Richard D. , Pitt William G. 
Published: December 2004

AbstractThe effects of water content and comonomer chemistry upon the adhesion of Pseudomonas aeruginosa to poly(hydroxyethyl methacrylate)‐based hydrogels were studied. Hydrogels which varied in swollen water content from 33–69 wt% were polymerized onto glass microscope slides pretreated with a vinyl silane. The hydrogel water content was varied by adding methacrylic acid (1–5 wt%) orN‐vinyl pyrrolidone (NVP, 10–25 wt%) or combinations of the two comonomers. The resulting hydrogel surfaces, which were 0.1 mm thick, transparent, and adherent to the glass slide, formed the test surfaces of laminar flow cells (Re = 1.3, wall shear rate = 1.6/s). The bacteria were grown for 8 h in tryptic soy broth (TSB), washed by filtration, and collected on 0.45‐μm filters, resuspended in phosphate buffered saline (PBS) at pH = 7.2, and recirculated through the flow cell and across the test surface at 0.85 mL/min for 2 h. Results show that P. aeruginosa adhered less to hydrogels with higher water contents. In the presence of TSB and possible poly(NVP) contamination, the concentration of adherent bacteria was reduced to low and uniform levels independent of the hydrogel chemistry. © 1993 John Wiley & Sons, Inc.
A histological and histomorphometrical investigation of fluorapatite, magnesiumwhitlockite, and hydroxylapatite plasma‐sprayed coatings in goats
Authors: Dhert W. J. A. , Klein C. P. A. T. , Jansen J. A. , van der Velde E. A. , Vriesde R. C. , Rozing P. M. , de Groot K. 
Published: December 2004

AbstractPlasma‐sprayed ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti‐6Al‐4V alloy (Ti) implants were evaluated histologically and histomorphometrically in a goat animal study. Cylindrical Ti‐6Al‐4V plugs were plasma‐spray‐coated with FA, MW, and HA. Noncoated, gritblasted Ti plugs served as controls. The plugs were implanted into the right femur and left humerus of 20 adults goats. The results were evaluated using descriptive histology and histomorphometry. The histomorphometry consisted of measurements of bone apposition and coating thickness. The results demonstrated that FA showed a high amount of bone apposition without signs of degradation or dissolution. MW showed considerable reduction in thickness and at 12 weeks an adverse tissue reaction. However, at 25 weeks the amount of bone apposition was significantly increased compared with the 12‐week implants. HA revealed considerable and progressive reduction in thickness and at 25 weeks a lower amount of bone apposition than FA and MW. At 12 weeks the Ti implants did reveal bone apposition, although frequently localized fibrous tissue was visible. At 25 weeks the Ti implants did not differ in bone apposition from the HA implants. Further studies are necessary on the effect of degradation or dissolution of HA on the compatibility with bone. © 1993 John Wiley & Sons, Inc.
Organoapatites: Materials for artificial bone. II. Hardening reactions and properties
Authors: Stupp Samuel I. , Mejicano George C. , Hanson Jacqueline A. 
Published: December 2004

AbstractThis article reports on chemical reactions and the properties they generated in artificial bone materials termed “organoapatites.” These materials are synthesized using methodology we reported in the previous article of this series1. Two different processes were studied here for the transition from organoapatite particles to implants suitable for the restoration of the skeletal system. One process involved the hardening of powder compacts by beams of blue light derived from a lamp or a laser and the other involved pressure‐induced interdiffusion of polymers. In both cases, the hardening reaction involved the formation of a polyion complex between two polyelectrolytes. In the photo‐induced reaction an anionic electrolyte polymerizes to from the coulombic network and in the pressure‐induced one, pressure forms the complex by interdiffusion of two polyions. Model reactions were studied using various polycations. Based on these results the organoapatite selected for the study was that containing dispersed poly(L‐lysine) and sodium acrylate as the anionic monomer. The organomineral particles can be pressed at room temperature into objects of great physical integrity and hydrolytic stability relative to anorganic controls. The remarkable fact about these objects is that intimate molecular dispersion of only 2–3% by weight organic material provides integrity to the mineral network in an aqueous medium and also doubles its tensile strength. This integrity is essentially nonexistent in “anorganic” samples prepared by the same methodology used in organoapatite synthesis. The improvement in properties was most effectively produced by molecular bridges formed by photopolymerization. The photopolymerization leads to the “hardening” of pellets prepared by pressing of organoapatite powders. The reaction was found to be more facile in the microstructure of the organomineral, and it is potentially useful in the surgical application of organoapatites as artificial bone. © 1993 John Wiley & Sons, Inc.
Variations between biomer lots. 2: The effect of differences between lots on in vitro enzymatic and oxidative degradation of a commercial polyurethane
Authors: Tyler Bonnie J. , Ratner Buddy D. 
Published: December 2004

AbstractIn vitro degradation of two lots of Biomer, a commercial poly(ether urethane urea), has been investigated in order to understand possible mechanisms for in vivo degradation. Two lots of Biomer, BSUA001 and BSP067, were used in the study. Lot BSUA001 contained a poly(diisopropylaminoethyl‐methacrylate), an ultraviolet‐stabilizing additive. This additive was absent in lot BSP067. Samples of each lot were exposed to two hydrolytic enzymes, papain and leucine aminopeptidase, and to hydrogen peroxide for 24 h. The extent of degradation was assessed using high‐pressure gel permeation chromatography and x‐ray photoelectron spectroscopy (XPS). Statistically significant changes in the molecular‐weight distribution occured in lot BSP067 for all three treatments. Only the hydrogen peroxide treatment resulted in statistically significant changes in the molecular weight of lot BSUA001. XPS data for samples of lot BSUA001 that had been treated with hydrogen peroxide revealed the formation of nitroso groups and protonated amines at the surface. The data suggest that surface chemistry is important for enzyme catalyzed degradation, while permeability is important for degradation by hydrogen peroxide. © 1993 John Wiley & Sons, Inc.
Platelet deposition onto polymeric surfaces during shunting
Authors: Fujimoto Keiji , Minato Masao , Tadokoro Hideki , Ikada Yoshito 
Published: December 2004

AbstractIn an attempt to develop blood‐contacting tubes that can be applied for short‐term uses with a reduced heparin concentration or, ideally, without heparinization, we evaluated the blood compatibility of polymeric materials with a rabbit ex vivo shunt model. The shunt tubes employed were made of silicone, plasticized poly(vinyl chloride) (PVC), and segmented poly(ether urethane) (PU). In addition, two kinds of surface‐modified tube were used: poly(vinyl alcohol) (PVA)‐coated PVC and poly(dimethylacrylamide) (PDMAA)‐grafted PU. The ex vivo shunt results correlated well with protein adsorption and platelet adhesion in vitro. The following order for the extent of platelet deposition was given, irrespective of the blood‐contacting duration: PDMAA‐grafted PU < PVA‐coated PVC < PU < silicone, PVC. It is likely that many platelet aggregates detached from the PVA‐coated PVC surface. For PDMAA‐grafted PU, no trace of detachment of aggregates could be detected on any of the SEM photographs. The number and morphology of blood cells adhered onto the tube surfaces during ex vivo shunting were dependent on the kind of polymer surfaces, the blood exposure time, and the flow rate of blood. © 1993 John Wiley & Sons, Inc.
Dissolution and scanning electron microscopic studies of Ca,P particle‐containing bioactive glasses
Authors: Kangasniemi I. M. O. , Vedel E. , de Blick‐Hogerworst J. , Yli‐Urpo A. U. , de Groot K. 
Published: December 2004

AbstractCalcium phosphate (Ca, P) precipitation behavior on the surface of two bioactive glasses and four bioactive glass composites—two with hydroxylapatite (Ca10(PO4)6(OH)2) and two with rhenanite (CaNaPO4)—were studied in simulated body fluid (SBF) and in Tris‐Buffer at 5, 8, 16, 24, 48, 72, and 144 h. The Weight loss of the materials was measured and the amount of precipitation was estimated using scanning electron microscopy with electrochemical detection (SEM‐EDX) analysis. The test was repeated for one glass and its respective rhenanite composite every 3 h until 60 h and thereafter every 10 h until 150 h in SBF. Atomic absorption spectroscopy, spectrophotometry, SEM‐EDX analysis, and pH measurements were performed on these samples. It is shown that in vitro the composite materials have a higher capacity for Ca, P precipitation than the glasses. Weight losses of the materials correlate well with their composition. Both the glass and Ca, P phases influence the precipitation mechanism and rate. Precipitation begins preferably from the glass phase. Ca, P particles clearly influence the time of onset and rate of precipitation. Cross‐sectional EDX analysis of the samples revealed an absence of a clear Sirich layer in glass AOBO (SiO2 53.9 mol %, Na2O 27.5, CaO 12.4, P2O5 6.2, Al2O3 0.0 and B2O3 0.0) composites. This was attributed to the presence of extra calcium and phosphate ions on the surface of the material. The ion‐concentration and pH change curves offered insight into the mechanism of precipitation. A connection was established between SEM‐EDX results and the release curves. Formation of an Si, Ca, Na film was observed that seemed to initiate the Ca, P precipitation. It is speculated that it is a characteristic of this particular glass composition. Two possible models for the mechanism of Ca, P precipitation are discussed. Phosphate polycondensation with silicate network or Ca binding to silicate network can both explain the results and it is assumed that in general both mechanisms play a role in the precipitation process. © 1993 John Wiley & Sons, Inc.
Compliance effects on small diameter polyurethane graft patency
Authors: Uchida Naoki , Kambic Helen , Emoto Hideto , Chen Ji‐Feng , Hsu Shan‐Hui , Murabayshi Shun , Harasaki Hiroaki , Nosé Yukihiko 
Published: December 2004

AbstractMicroporous compliance matched and noncompliant grafts were compared in a dog carotid artery interposition model. We fabricated 4 mm diameter sponge type polyurethane (Biomer) tubes 5 cm in length with a 0.5 mm wall thickness. The luminal surface was covered with a 50 μm coating of cross‐linked gelatin. Compliance was measured in vitro and in vivo by volume and vessel diameter changes. Over a mean arterial pressure range of 55–155 mm Hg, the diameter changes of grafts and stump arteries were measured in situ using an ultrasonic Hokanson device. Compliance matched grafts were found to have the same in vitro compliance values as the natural canine carotid at a mean arterial pressure of 100 mm Hg. Compliance matched and noncompliant grafts had values of 10.3 ± 1.3 and 0.9 ± 0.1 × 10−2 mm Hg, respectively. End to end arterial anastomoses were constructed between the graft and the host arteries.The use of synthetic grafts with matched compliance to the adjacent natural vessels has been advocated as the ideal solution to circumvent the problems of graft failure. These studies indicate that compliance values for compliance matched grafts decreased immediately after implantation (from 10.3 to 6.5 × 10−2 %/mm Hg) and within 6 weeks decreased to 3.6 × 10−2 %/mm Hg. The compliance values for noncompliant grafts remained constant throughout the test period.At autopsy all grafts showed a tightly adhered tissue capsule. The thickness of the anastomotic hyperplasia at the distal sites of compliance matched grafts was significantly different (P < .05) than that of the adjacent artery. The patency for compliant and noncompliant grafts was 64% and 50%, respectively. Evidence for polyurethane graft degradation was obtained by Fourier transform infrared spectroscopy and gel permeation chromatography analysis of patent explants. Compliance mismatch alone does not contribute to graft failure, however, material degradation, suture technique and/or capsule formation can play a contributory role although these were not tested directly. © 1993 John Wiley & Sons, Inc.