bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collagen fibers as a temporary scaffold for replacement of ACL in goats
Authors: Chvapil Milos , Speer Donald P. , Holubec Hana , Chvapil Thomas A. , King David H. 
Published: December 2004

AbstractACL substitutes made of braided or plied purified collagen fibers and cross‐linked with hexamethylenediisocyanate were implanted into a total of 14 adult goats to achieve resorption within 8 to 10 months. Two types of collagen fiber prostheses differing in degree of collegen purification were tested. The implants were harvested 2 to 11 months postimplantation, tested for mechanical strength, and evaluated by morphological methods. In the first group (n = 5), the less purified and less crosslinked collagen fiber ACL implant induced fast connective tissue ingrowth. At 6 months postimplantation, 40 to 60% of the collagen implant was resorbed. No studies on breaking strength were done in this group. In the second group, highly purified and more crosslinked ACL implants were less infiltrated by cells and were resorbed only by 10 to 20%. Still, the breaking strength was decreased to 10% of the original implant strength. In the second group, the fixation of the ACL implant in the bone tunnel with a bone wedge was insufficient (n = 6); however, additional fixation with metal screws was successful (n = 3). We conclude that cross‐linked collagen fibers alone cannot be used as a safe ACL substitute as they quickly lose mechanical strength despite limited biodegradation. © 1993 John Wiley & Sons, Inc.
Interaction of heparin with polyallylamine‐immobilized surfaces
Authors: Ma Xinghang , Mohammad Syed Fazal , Kim Sung Wan 
Published: December 2004

AbstractA new method to bind ionically and remove heparin from solution and dilute serum is described. Utilizing cellulose diacetate (CA) as the polymer substrate, a cationic polymer chain—poly(allylamine)‐PALA—was immobilized directly onto the CA surface and onto the surface using poly(ethylene glycol) (PEG) spacer groups. The ionic interaction between the anionic heparin molecule and the cationic PALA polymer is specific and effective to remove haparin from the bulk solution. The binding properties of heparin onto the PALA and PEG‐PALA surfaces were examined. The effects of PEG spacers on heparin binding onto the PALA‐immobilized surface were investigated by varying the MW of PEG spacers. PALA (MW 8500)‐immobilized surfaces exhibited enhanced heparin binding. The maximum heparin binding was observed in the region of PEG MW 2000–4000. For the high‐molecular‐weight PALA (MW 50,000)‐immobilized surfaces, heparin binding was independent of the molecular weight of PEG. PEG spacers were also evaluated for their ability to prevent or decrease protein (albumin) adsorption. It was observed that at high albumin concentrations, the adsorption of proteins decreased with increasing chain length of PEG, up to MW 3400. These observations suggest that low‐molecular‐weight PALA (MW 8500)‐immobilized CA surfaces with PEG spacers (MW 3400) may provide increased heparin binding capacity and decreased protein adsorption. © 1993 John Wiley & Sons, Inc.
Protein adsorption to poly(ether urethane ureas) modified with acrylate and methacrylate polymer and copolymer additives
Authors: Brunstedt Michael R. , Ziats Nicholas P. , Robertson Steven P. , Hiltner Anne , Anderson James M. , Lodoen Gary A. , Payet C. R. 
Published: December 2004

AbstractTo understand better blood interactions with poly(ether urethane urea) (PEUU) materials, a radioimmunoassay and whole or diluted human plasma were used to characterize the presence of fibrinogen, immunoglobulin G, factor VIII/von Willebrand factor, Hageman factor on (factor XII), and albumin on a PEUU formulation and on PEUU formulation modified with the amphiphilic additive Methacrol 2138F (co[diisopropylaminoethyl methacrylate (DIPAM)/decyl methacrylate] [3/1]), or with hydrophobic acrylate or methacrylate polymer or copolymer additives. The protein adsorption assay showed that PEUU films loaded or coated with Methacrol 2138F (Methacrol) or homopoly‐DIPAM (h‐DIPAM) adsorbed significantly lower amounts of the studied proteins than did either the base PEUU formulations or the PEUUs loaded with th more hydrophobic acrylate or methacrylate polymer additives. Experiments with Methacrol‐loaded PEUUs, where the loading of Methacrol was varied from 0.25 wt% to 20.0 wt% showed that the adsorption of each of the characterized proteins did not vary significantly throughout the Methacrol loading range, and that all Methacrol‐loaded PEUU formulations adsorbed significantly lower amounts of the studied proteins than did the unloaded PEUU. Phase separation within the additive loaded PEUUs was characterized by scanning electron microscopy (SEM). The solubility parameters of the additives, as well as of the base PEUU, were calculated and used to interpret differences in phase separation of the additive modified PEUUs. The analysis showed that additives of lower solubility parameter phase‐separated into fewer large microdroplets within the PEUU matrix. SEM analysis also showed that additive microdroplets were not present on the air side surface of loaded PEUUs. To explain the differences in protein adsorption to the air side of additive loaded PEUUs when compared to the base PEUU, it was assumed that the additives near this region of the solvent swollen PEUU matrix may have migrated to, at or near the PEUU–air interface during film formation, creating an additive enriched PEUU surface region. Once at this surface region, it was suggested that dynamic surface reorientation in response to an aqueous medium ensured that the additives were able significantly to influence protein adsorption behavior only if they interacted with aqueous media more favorably than the PEUU. © 1993 John Wiley & Sons, Inc.
Extracellular matrix analogs as carriers for growth factors: In vitro fibroblast behavior
Authors: Roy France , DeBlois Chantal , Doillon Charles J. 
Published: December 2004

AbstractRepair of connective tissue involves interactions between growth factors (GFs) and extracellular matrix (ECM) molecules. On the other hand, biological biomaterials could be used to carry and deliver GFs to stimulate wound healing. In the present study, fibroblasts were cultivated in a serum‐free culture medium onto collagen (type I), hyaluronic acid, chondroitin sulfate, fibronectin, or fibrin. FGF, EGF, or PDGF was incorporated within those substrates. Using immuno‐ and radiolabeling assays, the distribution of GFs within the ECM analogs was relatively uniform and GFs retained in substrates were dependent on the substrates. Fibroblast replication was determined by the incorporation of [3H]‐thymidine and compared to control groups. On collagen or chondroitin sulfate, the incorporation of GFs did not significantly improve cell proliferation. On hyaluronic acid, the incorporation of FGF and PDGF enhanced cell replication at 48 h. The incorporation of PDGF in fibronectin enhanced cell replication. On fibrin, the incorporation of PDGF, EGF, and FGF significantly enhanced cell replication. However, cell replication on FGF‐incorporated fibrin was higher by 48 h than that on fibrin in the presence of FGF‐supplemented culture medium. Fibrin sustains the biological activity of GFs, FGF in particular, and can be a carrier for GF that stimulates cell replication. © 1993 John Wiley & Sons, Inc.
Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins
Authors: Beatty M. W. , Swartz M. L. , Moore B. K. , Phillips R. W. , Roberts T. A. 
Published: December 2004

AbstractSeven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane‐based polymers sorbed substantially more water than the aromatic‐based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water. © 1993 John Wiley & Sons, Inc.
Fluoroalkylethyl silane coating as a moisture barrier for dental ceramics
Authors: Rosenstiel S. F. , Denry I. L. , Zhu W. , Gupta P. K. , van der Sluys R. A. 
Published: December 2004

AbstractThe performance of dental ceramics is reduced in wet environments due to stress‐corrosion limiting restoration lifetime. As analysis suggests that fracture is typically initiated from the internal surface, placement of a thin coating before a restoration is cemented to place may prevent fracture if it acts as a moisture barrier. Of coating we tested, a fluoroalkylethyl silane (du Pont MPD‐7680) showed promise. This study aimed to test a range of concentrations on glass and to determine any strength improvement on dental ceramics. Glass slides (n = 8–9) were indented (29‐N load) stored 24 h, etched, coated with 100, 50, and 25% fluorosilane in isopropyl alcohol, and air‐cured for 24 h. The slides were fractured on a biaxial fixture in water at 0.5 mm/min and maximum stresses calculated. Uncoated controls were tested in water and liquid N2 to determine the inert strength without stress‐corrosion. Results showed increasing mean strength from uncoated (53.6 MPa) to 100% (68.0 MPa) which compared to the 80.4 MPa inert strength. ANOVA showed P < .05. Subsequently the experiment was repeated on discs of three dental ceramics (n = 7–10): feldspathic (Ceramco), glass‐ceramic (Dicor MGC), high‐leucite (Optec) with the 100% solution only. Mean strength was significantly (P < .01) enhanced in the feldspathic (56.2 MPa, untreated, 70.7 MPa, treated) but not the high‐leucite (83.1, 83.0) or the glass‐ceramic (283.9, 271.4). Fluoroalkylethyl silane coating reduced stres‐corrosion in glass and feldspathic porcelain. It may be a practical approach to reducing fracture of ceramic restorations. © 1993 John Wiley & Sons, Inc.
Microencapsulated human hepatoma (HepG2) cells: In vitro growth and protein release
Authors: Uludag Hasan , Sefton Michael V. 
Published: December 2004

AbstractThe feasibility of a microencapsulation process ultimately for cell transplantation was investigated by encapsulating human hepatoma (HepG2) cells in hydroxyethyl methacrylate–methyl methacrylate (HEMA–MMA) membranes through an interfacial precipitation process. Changes in viability and metabolic activity as well as protein secretion by the encapsulated cells were studied in vitro. When encapsulated at either low or high density (1 or 5 × 106 cells/mL, respectively), HepG2 cells retained their active metabolic state and/or proliferated during the initial 1‐week period, after which a significant drop in cell viability was obtained. Encapsulati of a biological attachment substrate, Matrigel, along with the cells, however, resulted in rapid proliferation in both low and high density capsules with prolonged maintenance of an active metabolic state. The secretion of four model proteins (α1‐acid glycoprotein, α1‐antitrypsin, haptaglobin and fibrinogen) was demonstrated during the 2‐week study period for the Matrigel encapsulated cells. Furthermore, the encapsulated cells remained responsive to interleukin 6 (IL6), a physiological stimulator of plasma protein secretion, as determined by the elevated secretion of haptaglobin in response to IL6 treatment. We conclude that HEMA–MMA capsules, in the presence of an attachment substrate, provide a suitable environment for the growth and expression of differentiated functions of encapsulated hepatoma cells. © 1993 John Wiley & Sons, Inc.
A novel recovery system for cultured cells using plasma‐treated polystyrene dishes grafted with poly(N‐isopropylacrylamide)
Authors: Okano Teruo , Yamada Noriko , Sakai Hideaki , Sakurai Yasuhisa 
Published: December 2004

AbstractPoly(N‐isopropyl acrylamide) (PIPA Am) demonstrated a fully expanded chain conformation below 32°C and a collapsed, compact conformation at high temperatures. This unique temperature responsive polymer was grafted onto surfaces of commercial polystyrene dishes and used as temperature switches for creating hydrophilic surfaces below 32°C and hydrophobic surfaces above 32°C. Cells attachment and the growth of bovine endothelial cells and rat hepatocytes on PIPA Am‐grafted surfaces at 37°C demonstrated similar behavior to the commercialized culture dishes. Both cell types were observed to detach from the PIPA Am‐grafted surface simply by reducing the temperature below the polymer transition temperature (collapse). Cells recovered by this method maintained substrate adhesivity, growth, and secretion activities nearly identical to those found in primary cultured cells in contrast to the compromised function found in cultured cells damaged by trypsinization. These results provide strong evidence that PIPA Am‐grafted surfaces, as thermal switches are very effective for reversing cell attachment and detachment without cell damage. Properties of cell culture surfaces can be readily transformed by this technique reversibly into hydrophilic and hydrophobic coatings of PIPA Am‐grafted polymers. © 1993 John Wiley & Sons, Inc.
Poly(ethyleneimine) modified filters for the removal of leukocytes from blood
Authors: Bruil Anton , Oosterom Hieke A. , Steneker Ingeborg , Al Bert J. M. , Beugeling Tom , van Aken Willem G. , Feijen Jan 
Published: December 2004

AbstractPolyurethane membrane filters and filters coated with poly(ethyleneimine) were used to investigate the influence of leukocyte adhesion during filtration. Treatment of the filters with an aqueous solution of 1% (w/v) poly(ethyleneimine) (PEI) led to the introduction of amine groups at the filter surfaces, as was confirmed by X‐ray photoelectron spectroscopy. The modification procedure did not significantly change the porous structure in the filters, as was demonstrated by SEM and porometry. Using 14C‐labeled poly(ethyleneimine) it was shown that nearly a complete coverage (∼0.1 mg/m2) was achieved that did not desorb from the filter surface during contact with blood plasma. When the filtration was carried out with purified leukocytes in the absence of red cells, platelets, and blood plasma, the number of cells removed by modified filters (>95%) was significantly higher as compared to the removal with unmodified filters (∼80%). However, no significant differences between the filters were found when the filtration was performed with whole blood. This finding was unexpected, because it was shown before that immobilization of poly(ethyleimine) on solid polyurethane film, surfaces promoted the adhesion of leukocytes from whole blood. Apparently, the adhesive properties of the PEI diminish during filtration. Filter coating of commercial leukocyte filters composed of polyester fibers also had no effect on the removal of leukocytes from whole blood. It was postulated that morphological factors, such as filter shape, roughness, tortuosity, and porosity rather than the physicochemical properties of the filter surface influence cell adhesion to the filter surface, and through that the filtration process. © 1993 John Wiley & Sons, Inc.
Scanning electrochemical microscopy of metallic biomaterials: Reaction rate and ion release imaging modes
Authors: Gilbert Jeremy L. , Smith Samuel M. , Lautenschlager Eugene P. 
Published: December 2004

AbstractThe Scanning Electrochemical Microscope (SECM) is a nonoptical scanning microscopic instrument capable of imaging highly localized electrical currents associated with charge transfer reactions on metallic biomaterials surfaces. The SECM operates as an aqueous electrochemical cell under bipotentiostatic control with a microelectrode and sample independently biased as working electrodes. Microelectrode current and position is recorded as it is scanned very near a metallurgically polished planar sample surface. To date, the SECM has imaged metallic biomaterials surfaces in oxygen reaction rate imaging (ORRI) and ion release and deposition imaging (IRDI) modes. In ORRI, sample and microelectrode are biased at sufficiently negative potentials to reduce absorbed oxygen. As the microelectrode scans areas of active oxygen reduction, localized diffusion fields with decreased oxygen solution concentrations are encountered and resultant decrements in microelectrode current are observed. In IRDI mode the sample is positively biased and the microelectrode is negatively biased. The microelectrode detects anodic dissolution products with highest currents being observed over the most active areas. Performance of the SECM has been evaluated on Ni minigrids, γ‐1 Hg‐Ag dental amalgam crystals, and sintered beads of Co‐Cr‐Mo alloy which represent significantly different geometries and corrosion processes to help demonstrate the potential of this instrument. The SECM is a valuable tool for imaging microelectrochemical processes on the surfaces of metallurgically polished metallic biomaterials samples and a wide variety of other surfaces of biological interest where charge transfer reactions occur. The SECM allows selective biasing of metallic biomaterials surfaces and Faradaic reactions can be selectively imaged while the surface is in the active, passive, or transpassive state. © 1993 John Wiley & Sons, Inc.
Immobilization of poly(ethylene glycol) onto a poly(vinyl alcohol) hydrogel: 2. Evaluation of thrombogenicity
Authors: Llanos Gerard R. , Sefton Michael V. 
Published: December 2004

AbstractImmobilized polyethylene glycol (PEG) reduced the amount of bovine serum albumin (BSA) adsorbed on polyvinyl alcohol (PVA) hydrogel, but did not reduce the platelet reactivity of the hydrogel surface. PEG, molecular weight (MW) 2000 or 5000, with or without a monomethoxy end group, was covalently bound to glutaraldehyde‐crosslinked PVA either through a cyclic acetal or an urethane functional group with a surface coverage of 70% (as measured by x‐ray photoelectron spectroscopy [XPS]). Immobilization of monomethoxy‐PEG via a cyclic acetal reduced BSA adsorption to PVA from 11 ± 2 nmol/m2 to 3.9 ± 0.3 nmol/m2 and 3.3 ± 0.3 nmol/m2 for MW 2000 and 5000, respectively. Similarly, urethane bound PEG reduced adsorption to 3.5 ± 1.6 nmol/m2 for MW 2000 and 5.4 ± 1.0 nmol/m2 for MW 5000. Whole blood clotting times of PVA (using a Chandler loop) were not affected by covalently linked PEG, although the initial rate of thrombin generation at the surface, measured using a fluorogenic substrate, was marginally reduced; a rate constant of 4.2 ± 0.1 cm/sec and 3.5 ± 0.1 cm/sec were obtained for MW 2000 and 5000, respectively, compared to 5.6 ± 1.0 cm/sec for PVA. Ex vivo evaluation using a canine arteriovenous shunt revealed that the hydrogel, with or without bound PEG, reduced circulating platelet levels by 35‐70% after 4 days. The initial fractional rate of platelet destruction determined from measurement of platelet cyclooxygenase activity, indicated that cyclic acetal or urethane bound PEG of either molecular weight had no effect on platelet consumption produced by PVA. The PEG hypothesis at least as it relates to platelet interactions may need to be evaluated further in the light of these results. © 1993 John Wiley & Sons, Inc.
Mechanisms of polymer degradation in implantable devices. 2. Poly(DL‐lactic acid)
Authors: Ali S. A. M. , Doherty P. J. , Williams D. F. 
Published: December 2004

AbstractThe hydrolytic degradation of poly(DL‐lactic acid) in an aqueous environment in which hydroxyl radicals have been generated has been investigated. Different methods (gel permeation chromatography, differential scanning calorimetry, and scanning electron microscopy) were employed to study the mechanisms of degradation of this amorphous physiologically absorbable polymer. The data indicated that the hydroxyl radical is likely to be a significant factor in the degradation of this polymer. © 1993 John Wiley & Sons, Inc.
Effect of polyol type on the physical properties and thrombogenicity of sulfonate‐containing polyurethanes
Authors: Silver James H. , Marchant John W. , Cooper Stuart L. 
Published: December 2004

AbstractPolyetherurethanes (PEUs) based on polytetramethylene oxide (PTMO) as the polyol, and derivatized with propyl sulfonate functionality, have previously been shown to possess antithrombotic properties. In this article, the bulk physical properties of sulfonated and nonsulfonated polyurethanes containing either polyethylene oxide (PEO) or PTMO as the soft segment are studied. The in vitro shape‐change of platelets in contact with these surfaces, and their ex vivo bloodcontacting response are also investigated. It was found that PEO‐base was physically weaker than PTMO‐base, which is attributed to a lower degree or phase separation in the former. In the dry state, sulfonation enhanced the physical properties for PTMO‐containing polyurethane (PTMO‐SO3–0.20), but weakened the PEO‐containing polyurethane (PEO‐SO3–0.15). In vitro platelet spreading studies showed the lowest degree of platelet spreading and also the lowest platelet density on PEO‐base, while platelet spreading and density on the other three materials and polyethylene (PE) was greater. The thromboresistance of these materials was evaluated using a canine arteriovenous series shunt ex vivo. It was determined that PTMO‐SO3–0.20 was the least thrombogenic, followed by both PEO‐base and PEO‐SO3–0.15, and that PTMO‐base was the most thrombogenic. © 1993 John Wiley & Sons, Inc.