bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of sulfonation of segmented polyurethanes on the transient adsorption of fibrinogen from plasma: Possible correlation with anticoagulant behavior
Authors: Santerre J. P. , ten Hove P. , VanderKamp N. H. , Brash J. L. 
Published: December 2004

AbstractThe influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two‐step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted i n terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer–plasma “gel” hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anti‐coagulant activity on these materials.
High‐strength hydrogels based on N‐vinyl pyrrolidinone and 4‐t‐butyl‐2‐hydroxycyclohexylmethacrylate
Authors: Friends G. D. , Künzler J. F. , Ozark R. M. 
Published: December 2004

AbstractA nonionic, high‐water‐content, highstrength hydrogel based on N‐vinyl pyrrolidinone (NVP) and a novel hydrophilic‐bulky monomer, 4‐t‐butyl‐2‐ hydroxycyclohexylmethacrylate (TBCM), was developed. The TBCM was prepared in three relatively simple, high‐yield steps. The copolymerization of NVP with varying concentrations of TBCM resulted in transparent hydrogel films possessing a wide range in mechanical and physical properties. A copolymer composition of 91.7 parts NVP, 8.0 parts TBCM, and 0.3 parts ethylene glycol dimethacrylate (EGDMA) gave a transparent, flexible film possessing a water content of 86%, a modulus of 130 g/mm2, and a tear strength of 3.4 g/mm. In contrast, a copolymer composition of 49.7 parts NVP, 50 parts TBCM, and 0.3 parts EGDMA gave a transparent, hard hydrogel film possessing a water content of 26% and a modulus of 86,000 g/mm2. All of the high‐water co‐polymer compositions developed resulted in lysozyme uptake typical of nonionic high‐water‐content hydrogels and oxygen permeability levels greater than 50 (cm3 O2(STP) · cm)/(s · cm2 · mm Hg) × l0−11.
A finite element analysis of the push‐out test: Influence of test conditions
Authors: Dhert W. J. A. , Verheyen C. C. P. M. , Braak L. H. , De Wijn J. R. , Klein C. P. A. T. , de Groot K. , Rozing P. M. 
Published: December 2004

AbstractThe commonly used method for quantitative evaluation of the strength of a bone‐implant interface is the push‐out test. In order to give an impulse to standardization and to gain more insight in the biomechanics of the push‐out test, a finite element analysis of this test was performed. This study focused on the influence of test conditions on the push‐out results. The influence of the following four parameters on the interface stress distribution was tested: (a) clearance of the hole in the support jig, (b) Young's modulus of the implant; (c) cortical thickness; and (d) implant diameter. The distance between the implant and the support jig turned out to be very critical for the occurrence of peak stresses in the interface. Variations of the Young's modulus of the implants resulted in a wide range of interface shear stresses. Variation of the cortical thickness showed a reciprocal relationship between cortical thickness and interface shear stress. However, the interface stress distribution remained uniform under the specific test circumstances. These findings also hold for variations in implant diameter. The present investigation shows that the clearance of the hole in the support jig, and the Young's modulus of the implant are parameters which most strongly influence the interface stress distribution. The clearance of the hole in the support jig is the most critical parameter, but also the parameter that can be controlled most easily. Lack of standardization with regard to these parameters can lead to uninterpretable test results. It is recommended that the clearance of the hole in the support jig is at least 0.7 mm and that push‐out results are only compared with each other when materials with similar Young's modulus are concerned.
Compositional dependence of calcium phosphate layer formation in fluoride bioglasses®
Authors: Kim Cheol Y. , Clark A. E. , Hench L. L. 
Published: December 2004

AbstractBioglasses® form a double layer composed of apatite and a silica‐rich layer when placed in a simulated physiological solution as well as in living tissue [A. E. Clark, C.G. Pantano, and L. L. Hench, „Auger spectroscopic analysis of bioglass corrosion films,”︁ J. Am. Ceram. SOC., 59(1−2), 37−39 (1976).]. In the present work, the mechanisms of the calcium phosphate layer and the silica‐rich layer formation of fluoride Bioglassesm i n Tris‐buffer solution are studied as a function of the SiOz content. Fourier Transform Infrared Reflection Spectroscopy (FTIRS) is used to investigate the mechanism of formation of calcium phosphate and silica‐rich layers on the glass surface. Ion concentration in reacted solution and elemental depth profiles are obtained by Induced Coupled Plasma Atomic Emission Spectrometry (ICP) and Auger Elect on Spectroscopy (AES), respectGely. SiO bonds with one nonbridging oxygen and SiOSi bonds form at the early stage of reaction. Strong phosphorus ion uptake occurs when an amorphous calcium phosphate layer crystallizes. Glasses with high silica content (conventional glass) form the silica‐rich layer first followed by a calcium phosphate layer on top. However, glasses with low silica content (invert glass) form both layers simultaneously. The rate of apatite formation decreases with increasing SiOz content, especially in the region of conventional glass compositions. Ion release rates decreases as Si02 content increases, with a significant change occurring at the compositional boundary between invert and conventional glasses. © 1992 John Wiley & Sons, Inc.
PEO enhancement of platelet deposition, fibrinogen deposition, and complement C3 activation
Authors: Chaikof Elliot L. , Merrill Edward W. , Callow Allan D. , Connolly Raymond J. , Verdon Sylvie L. , Ramberg Karen 
Published: December 2004

AbstractWhereas it has been commonly thought that adding polyethylene oxide PEO to a surface would diminish the capacity of the surface to cause deposition of platelets and of fibrinogen, and to activate complement C3, we present data showing exactly the opposite. These unexpected results are obtained with low molecular weight (2000) PEO, and are not found with higher molecular weight (20,000) PEO.
Calcification of implanted vascular tissues associated with elastin in an experimental animal model
Authors: Paule W. J. , Bernick S. , Strates B. , Nimmi M. E. 
Published: December 2004

AbstractWe have previously studied the process of calcification in bioprosthetic porcine heart valves crosslinked with glutaraldehyde. Observations using light microscopy had indicated that calcification of elastic fibers occurs in implanted heart valves, in addition to calcification associated with collagen fibers. To determine the contribution of elastin to the process of calcification, small pieces of rabbit aorta were crosslinked with 0.2% glutaraldehyde, rinsed in buffer, and implanted subcutaneously in young adult male rats. Cross‐linked jugular vein implants were included as controls. After an implantation period of 1 month or longer, we observed many areas of calcification in the aortic media associated with elastin and fewer such areas associated with collagen. The elastin‐rich aortic tissues accumulated more calcium than venous tissues. Calcium deposits appeared similar in both allogeneic and xenogeneic implants. Calcified areas viewed under the electron microscope included intercellular nonfibrous material. Calcified areas involved predominantly the outer layers of elastic fibers. Calcific deposits included needle‐ like crystals of hydroxyapatite but often consisted of an amorphous flocculant material surrounded by crystals. The close spatial relationship of hydroxyapatite crystals and elastic membranes seen in this study may be relevant to the initiation of dystrophic calcification in glutaraldehyde cross‐linked aortic grafts. © 1992 John Wiley & Sons, Inc.
Introducing a selectively biodegradable filament wound arterial prosthesis: A short‐term implantation study
Authors: Cohn Daniel , Elchai Zohar , Gershon Baruch , Karck Mathias , Lazarovici Galila , Sela Jona , Chandra Mukul , Marom Gad , Uretzky Gideon 
Published: December 2004

AbstractThis article introduces a new compliant and selectively biodegradable filament wound vascular graft and reports the findings of a shorterm implantation study. A basic feature of filament winding is its ability to tailor and better control the mechanical properties of the prosthesis, so that a closer match with the anisotropic properties of native arteries is achieved. The elastomeric vascular grafts comprise poly(ether urethane urea) fibers (Lycra) embedded in a twocomponent matrix consisting of poly(ether urethane) (Pelle‐ thane) and a highly flexible poly(ethy1ene glycol)/poly(lactic acid) biodegradable segmented copolymer (PELA). Typical tensile modulus values fall in the few megapascals (MPa) range, this being comparable to that of natural arteries. The wound graft exhibits excellent handling and suturability characteristics as well as enhanced burst strength. Furthermore, due to its biodegradable constituent, the prosthesis combines minimal intraoperative blood loss and high healing porosity. The graft displays initially negligible in vitro water permeation, which increases gradually with time. In this short‐term study, the prostheses were implanted in the canine carotid, and their biological performance was compared to that of expanded Gore‐Tex. The luminal surface of the wound grafts was coated with a thin layer of pseudointima, strongly adhered to the prosthesis surface. Contrasting with the very stiff Gore‐Tex grafts, the filament wound prostheses retained their high compliance, being highly pulsatile upon explantation. Histological studies fully corroborated these findings, underscoring the healing properties of these new filament wound vascular prostheses. © 1992 John Wiley & Sons, Inc.
Human neutrophil response to short‐term exposure to F‐75 cobalt‐based alloy
Authors: Yang Jun , Shanbhag Arun , Lilien Jack , Black Jonathan 
Published: December 2004

AbstractThe effect of biomaterials on the activation of human neutrophils was studied. Human neutrophils were incubated with F‐75 cobalt‐based alloy or polystyrene microspheres of a nonphagocytosable size with two times total neutrophil plane surface area. Scanning and transmission electron microscope (SEM, TEM), energy dispersive x‐ray microanalysis (EDX), and graphite furnace atomic absorption spectroscopy (GFAAS) were used to analyze changes in cellular morphology and metal content. This report presents evidence that human PMNs display morphological changes related to foreign material challenge, including activation on F‐75 bead surfaces, pinocytosis of corrosion products, formation of intracellular vacuoles, degranulation, etc. Moreover, when PMNs were present, the corrosion release rate of F‐75 increased as much as three times over cell‐free controls. © 1992 John Wiley & Sons, Inc.
Neocartilage formation in vitro and in vivo using cells cultured on synthetic biodegradable polymers
Authors: Freed L. E. , Marquis J. C. , Nohria A. , Emmanual J. , Mikos A. G. , Langer R. 
Published: December 2004

AbstractCartilaginous implants for potential use in reconstructive or orthopedic surgery were created using chondrocytes grown on synthetic, biodegradable polymer scaffolds. Chondrocytes isolated from bovine or human articular or costal cartilage were cultured on fibrous polyglycolic acid (PGA) and porous poly(L)lactic acid (PLLA) and used in parallel in vitro and in vivo studies. Samples were taken at timed intervals for assessment of cell number and cartilage matrix (sulfated glycosaminoglycan [S‐GAG], collagen). The chondrocytes secreted cartilage matrix to fill the void spaces in the polymer scaffolds that were simultaneously biodegrading. In vitro, chondrocytes grown on PGA for 6 weeks reached a cell density of 5.2 × 107 cells/g, which was 8.3‐fold higher than at day 1, and equalled the cellularity of normal bovine articular cartilage. In vitro, the cell growth rate was approximately twice as high on PGA as it was on PLLA; cells grown on PGA produced S‐GAG at a high steady rate, while cells grown on PLLA produced only minimal amounts of S‐GAG. These differences could be attributed to polymer geometry and biodegradation rate. In vivo, chondrocytes grown on both PGA and PLLA for 1–6 months maintained the three‐dimensional (3‐D) shapes of the original polymer scaffolds, appeared glistening white macroscopically, contained S‐GAG and type II collagen, and closely resembled cartilage histologically. These studies demonstrate the feasibility of culturing isolated chondrocytes on biodegradable polymer scaffolds to regenerate 3‐D neocartilage. © 1993 John Wiley & Sons, Inc.
The effect of calcium phosphate ceramic composition and structure on in vitro behavior. I. Dissolution
Authors: Ducheyne Paul , Radin Shulamith , King Linda 
Published: December 2004

AbstractSynthetic calcium phosphate ceramic (CPC) surfaces can be transformed to a biological apatite through a sequence of reactions which include dissolution, precipitation, and ion exchange. By virtue of the reactions being material‐dependent, it is important to determine parametric rate effects. In this study we focused on the effect of stoichiometry and crystal structure of CPCs on the dissolution kinetics. Monophse, biphase, and multiphase CPCs with a Ca/P ratio equal to or greater than 1.5 were studied. The experiments were performed in a calcium‐ and phosphate‐free Tris buffer solution at pH 7.3. The dissolution behavior of the CPCs studied was found to vary over a wide range. The dissolution rate of the monophase CPCs increased in the order of stoichiometric hydroxyapatite, calcium deficient hydroxyapatite, oxyhydroxyapatite, β‐tricalcium phosphate, α‐tricalcium phosphate, and tetracalcium phosphate. Dissolution of biphase and multiphase CPCs increased prorated the concentration of more soluble component. © 1993 John Wiley & Sons Inc.
Measurement of intracellular hydrogen peroxide induced by biomaterials implanted in a rodent air pouch
Authors: Krause Tyrone J. , Robertson Fredika M. , Greco Ralph S. 
Published: December 2004

AbstractBiomaterials elicit an inflammatory response that is undoubtedly a factor in their heading and in the complications associated with their use. Herein, we report the modification of a rat air pouch in which we measured the production of intracellular hydrogen peroxide by inflammatory cells adherent to the surfaces of silicone elastomer (SE) and expanded polytetrafluoroethylene (ePTFE). We used the fluorescent probe dichlorofluorescein diacetate (DCFH‐DA) to measure the intracellular production of hydrogen peroxide 2 and 7 days after implantation. After 2 days, host cells adherent to ePTFE produced almost 3.5 times more hydrogen peroxide than did cells adherent to SE (P < .001). By 7 days, the H2O2 production on cells adherent to ePTFE had decreased while that on cells adherent to SE was unchanged. These data indicate that the air pouch is a good alternative to other in vivo models for studies of the biological reactions induced by biomaterials. © 1993 John Wiley & Sons, Inc.
A new type of biomaterial for artificial skin: Dehydrothermally cross‐linked composites of fibrillar and denatured collagens
Authors: Koide M. , Osaki K. , Konishi J. , Oyamada K. , Katakura T. , Takahashi A. , Yoshizato K. 
Published: December 2004

AbstractA new type of biomaterial for artificial skin was developed as a form of sponge by combining fibrillar collagen (F‐collagen) with gelatin. The sponge was physically and metabolically stabilized by introducing dehydrothermal cross links. To get the final product, various conditions in the preparation of sponges were evaluated by in vitro cellular responses and in vivo tissue reactions. Fibroblasts placed on a sponge of gelatin attached themselves to it, migrated well into the sponge, and remained inside it for at least 7 days. However, sponges of gelatin showed structural instability for hydrolytic degradation by the cells. Most fibroblasts appeared not to penetrate into the interior of a sponge of F‐collagen but to remain on its surface when fibroblasts were placed on the sponge, suggesting poor attraction of F‐collagen revealed an intense infiltration of neutrophils into the sponge, indicating F‐collagen as an inducer of the inflammatory reaction. These aggravating characters of F‐collagen sponges were greatly improved by blending gelatin with F‐collagen. The new type of collagen‐based biomaterials developed in the present study is expected to become a useful matrix substance for artificial skin. © 1993 John Wiley & Sons, Inc.
Thrombin and albumin adsorption to PVA and heparin–PVA hydrogels. 2: Competition and displacement
Authors: Smith Barbara A. H. , Sefton Michael V. 
Published: December 2004

AbstractThrombin adsorption to polyvinyl alcohol (PVA) was different from its adsorption to polyethylene (PE)—not so much in amount, but in its affinity. Thrombin was more easily displaced from polyethylene and its adsorption was more readily prevented by prior or simultaneous exposure to albumin. From PVA (or heparin–PVA), only ∼ 30% of the adsorbed protein could be removed by a series of eluents, including even harsh ones such as 2.5M NaOH and 6M guanidine;>85% could be removed from PE. Thrombin adsorption to PVA was not affected by the presence of BSA in solution or at the surface, but was virtually prevented on PE by preexposure to or adsorption with BSA. Heparin‐PVA was not much different than PVA in most of these experiments, but did exhibit a “Vroman effect”. In the absence of fibringen or antithrombin III, there was a maximum in thrombin adsorption from plasma at a plasma concentration of 1%. The behavior on this surface was dependent on both exposure time and protein concentration. These studies highlight the complexity of the interaction between plasma proteins and polymer surfaces (particularly hydrogel surfaces) and the difficulty of obtaining a clear picture of what happens when a single protein interacts with a polymer in the presence of other proteins. © 1993 John Wiley & Sons, Inc.
Enzyme–biomaterial interactions: Effect of biosystems on degradation of polyurethanes
Authors: Santerre J. P. , Labow R. S. , Adams G. A. 
Published: December 2004

AbstractEnzyme‐induced liberation of hard‐segment‐containing components from polyurethanes was evaluated using two 14C‐labeled polyurethanes. A polyester ureaurethane and polyether urea‐urethane were synthesized from toluene‐2,4‐diisocyanate (TDI)/ polycaprolactone diol (PCL) or TDI/polyethylene glycol (PEO) with 14C‐labeled ethylene diamine. Both materials were characterized using electron spectroscopy for chemical analysis (ESCA), differential scanning calorimetry (DSC), size exclusion chromotography, and material chemistry by Fourier transform infrared (FTIR) spectroscopy. Biodegradation assays were carried out using cholesterol esterase (CE), collagenase (CO), cathepsin B (CB), and xanthine oxidase (XO) at the pH optimum conditions for each enzyme at 37°C. Biodegradation was analyzed by monitoring the release of radiolabel, by weight change, and by surface analysis using scanning electron microscopy. The polyester urea‐urethane was shown to be susceptible to enzymatic degradation above the effect of the buffer control solution by the CE but not by the other enzyme systems as monitored by radiolabel released. In the initial period of incubation, the rate of degradation was increased for all systems, including buffer controls; however, the rates dropped off rapidly by day 28. The change in weight data for the polyester urea‐urethane and polyether urea‐urethane showed no enzyme‐dependent biodegradation above the buffer controls. However, in sodium acetate buffer at pH = 5, the polymers showed a significant weight loss relative to other buffers. In conclusion, this study showed that the biological component responsible for the onset of the biodegradation process is more likely the result of a multitude of biologically mediated compounds acting synergistically, with the process being enhanceds by physical parameters such as material dissolution. In addition characterization of surface and bulk chemistry as well as material structure evaluation have been shown to be essential to interpret degradation data. © 1993 John Wiley & Sons, Inc.
Organoapatites: Materials for artificial bone. III. Biological testing
Authors: Stupp Samuel I. , Hanson Jacqueline A. , Eurell Jo Ann , Ciegler Glenn W. , Johnson Ann 
Published: December 2004

AbstractThis article reports on the in vivo testing of new artificial bone materials we have termed “organoapatites.” These materials consist of mineral networks in which organic polymers are intimately dispersed by nucleation and growth of apatite crystals from a mother liquor containing the organic substances. Organoapatites were tested as implants in adult canine cortical bone for periods in the range from 12–35 weeks and fluorochromes were used in the model to investigate the kinetics of bone growth or repair. The analysis of histological samples was carried out using histomorphometric methods as well as fluorescence microscopy. Results showed excellent apposition of poly(amino acid) organoapatites with mineralized bone and fibrous encapsulation when a synthetic polyelectrolyte was the only organic component. This observation suggests that the molecularly dispersed organic dopant amounting to only 2–3% by weight of the microstructure can play a critical role in the tissue response to the implant. Relative to apatite controls, organoapatites were also found to have greater resistance to fragmentation in vivo and those containing amino acid units revealed interfacial bioerosion accompanined by regeneration of mineralized tissue. Design of organoapatite compositions and microstructures may therefore be useful in achieving the specific rate of biological response which is clinically desired. © 1993 John Wiley & Sons, Inc.