bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of the rate of thrombin production in human palsma in contact with different materials
Authors: Rollason Gordon , Sefton Michael V. 
Published: May 2005

AbstractThrombin production in plasma in contact with various materials was consistent with a first‐order autocatalytic model (d[T]/dt = k,[T]; [TI] = thrombin concentration, t = time, k, = thrombin production rate constant) since the initial portion of a semilogarithmic plot of thrombin concentration against time was linear. Thrombin concentration was measured in clotting plasma (phospholipid enhanced or plateletrich plasma) using fluorogenic substrate (BMCA) by aliquot sampling at various intervals or more conveniently by monitoring cumulative fluorescence. The latter was generated by the action, on BMCA incubated in the clotting plasma, of the thrombin as it was generated. The thrombin concentration was determined from the first derivative of the S‐shaped cumulative fluorescence curve. kp, was greater for glass (7.92 × 10−3 cm/than) for the other materials (polypropylene, polystyrene, polyethylene and PVA; kp, ∼3.1 × 10−3cm/s) in plasma with cephalin without flow. A kp, for heparin PVA could not be determined since the thrombin concentration was too low to be quantified. A larger difference between polyethylene and PVA was noted with platelet‐rich plasma without flow while lower values (1.0 × cm/s) were noted in a flow system but at a higher surface to volume ratio. The first‐order rate constant can be used in simple models relating production of thrombin at a wall of a tube to its mass transfer away from the wall in flowing blood. One such model predicts that the concentration of thrombin at the wall should become infinite at the point in the tube when the mass transfer coefficient equals kp. According to this model, kp on the order of cm/s would be a useful target for a nonthrombogenic material.
Blood compatibility of SUUU‐PEO‐heparin graft copolymers
Authors: Park Ki Dong , Kim Won Gon , Jacobs Harvey , Okano Teruo , Kim Sung Wan 
Published: May 2005

AbstractBiological responses to heparinized segmented polyurethaneurea (SPUU‐PEO‐Heparin) were evaluated in uitro and ex vivo. In uitro assays involved plasma protein adsorption, platelet adhesion, and release reaction studies. In addition, an ex vivo rabbit arterio‐artery (A‐A) shunt experiment was also performed to measure occlusion times of the heparinized surfaces. All SPUU‐PEO‐Heparin surfaces demonstrated less protein adsorption than Biomer® and protein adsorption patterns similar to SPUU‐PEO surfaces. Platelet adhesion and release studies demonstrated that both SPUU‐PEO‐Heparin and SPUU‐PEO surfaces adsorbed less platelets and inhibited platelet release, as compared to Biomerm. These findings correlated with reduction in protein adsorption observed for the modified surfaces. In low flow rate ex‐vivo A‐A shunt experiments, all heparinized surfaces prolonged occlusion time longer than controls. However, SPUU‐PEO surfaces did not prolong occlusion time whencompared to BiomerB, although these surfaces suppressed protein adsorption and platelet interaction in vitru. The improved blood compatibility of SPUU‐PEO‐Heparin surfaces attest to the usefulness of this approach in improving the blood compatibility of blood contacting surfaces.
TNF and IL‐1 generation by human monocytes in response to biomaterials
Authors: Cardona Mario A. , Simmons Richard L. , Kaplan Sandra S. 
Published: May 2005

AbstractThe biocompatibility of surgically implanted materials may be compromised as a consequence of inflammatory reactions associated with phagocyte activation. Two important mediators of the inflammatory response are Interleukin‐1 (IL‐1) and tumor necrosis factor (TNF), both of which exert a wide range of biologic effects on many cells. This study was designed to evaluate the release of these cytokines by human monocytes (HM) brought into contact with four biomaterials utilized in clinical practice: polyurethane, expanded polytetrafluorethylene (ePTFE), Dacron velour, and woven Dacron. In vifro cultures for the generation of IL‐1 and TNF by HM in the presence of the above biomaterials were established by exposing cells to each bio material in the presence and absence of lipopolysaccharide (LPS) with harvest of supernatants after 6 or 18 h. These studies showed that in the absence of LPS, IL‐1 was released only by Dacron velour and woven Dacron associated monocytes while TNF was secreted in response to all of the materials. When LPS was present, however, monocytes associated with all of the materials released IL‐1; and TNF release was greatly augmented. Further, the quantity of released cytokine was directly related to the duration of the association time. This study demonstrated that HM in association with various biomaterials were ctivated to produce both TNF and IL‐1 and that the addition of nanogram quantities of LPS, such as would be produced if infection were present, greatly increased the amount of cytokines released.
Role of serum vitronectin and fibronectin in adhesion of fibroblasts following seeding onto tissue culture polystyrene
Authors: Steele John G. , Johnson Graham , Underwood P. Anne 
Published: May 2005

AbstractThe suitability of polymeric biomaterials as surfaces for the attachment and growth of cells has often been investigated in tissue culture. In this study the contribution that adsorption of serum fibronectin (Fn) or vitronectin (Vn) make to the attachment and spreading of fibroblast cells during the first 90 min following seeding was determined for two modified tissue culture polystyrenes, as model biomaterial surfaces. The amount of serum Vn and Fn which adsorbed onto tissue culture grade polystyrene (TCP) from different serum concentrations over the range of 0.1‐30% (v/v) were determined and compared to attachment of cells of the BHK‐21 and HT1080 fibroblast lines. There was no simple correlation between the amount of Fn or the amount of Vn adsorbed and cell attachment and spreading. The requirement for Fn or Vn for attachment and spreading of BHK‐21 or HT1080 cells onto modified polystyrene (either TCP or to Primaria) during the first 90 min of cell culture was directly tested by selective removal of Fn or Vn from the serum prior to addition to the culture medium. Attachment and spreading of BHK‐21 or HT1080 cells onto TCP or Primaria surfaces were reduced in a concentration dependent manner when the cells were seeded in medium containing 2% (v/v) or higher concentrations of Vn‐depleted serum. BHK‐21 cells or HT1080 cells seeded in medium containing Fn‐depleted serum (which contained Vn) attached and spread onto TCP or Primaria. Both BHK‐21 cells and HT1080 cells failed to attach to TCP or Primaria when seeded in medium containing serum depleted of both Vn and Fn. The requirement for serum Vn or Fn for fibroblast attachment to TCP was also tested using cells of a human dermal fibroblast strain. The attachment of the dermal fibroblasts to TCP during the first 90 min of culture was not decreased by depletion of Vn from the 15% (v/v) serum, but there was a reduction in the proportion of the attached cells which had spread. Selective depletion of serum Fn did not have any effect on either cell attachment or spreading. Our results show that for fibroblast cells, particularly with cell lines such as BHK‐ 21 or HT1080 but also with cell strains, the first binding of cells onto tissue culture polystyrene when plated in medium containing serum is a result of adsorption onto the surface of serum Vn. The adsorption of serum Vn onto the surface overcomes the effect of serum components which tend to decrease cell attachment.
Bone induction by demineralized bone particles: Long‐term observations of the implant–connective tissue interface
Authors: Hagen J. W. , Semmelink J. M. , Klein C. P. A. T. , Prahl‐Andersenc B. , Burger E. H. 
Published: May 2005

AbstractAllogeneic demineralized bone (DB) powder was applied to subcutaneous pockets and cranial defects of rats and histological, histomorphometrical, and radiological evaluation was performed one to 52 weeks after implantation. In both type of implants cartilage formation was observed after 1 week between DB particles and in former vascular channels and crevices within the particles. Foci of bone formation were observed after 2 weeks in the center of the implant. Remineralization of DB particles only occurred in close contact with the new bone tissue by which they became incorporated, indicating that remineralization of DB is a continuation of a process which has started in live bone. At all times, the interface between implant and connective tissue of the host consisted of a layer of nonremineralized DB particles embedded in fibrous connective tissue. This rim was thinner at the dura‐mater‐side in the cranial implants, compared with the skin‐side of the same implants as well as all sides of the subcutaneous implants. The rim became thinner with time but never disappeared completely. The outer contour of the mineralized implant sometimes ran right through a DB particle. A critical concentration of bone‐inducing agent leaking from DB particles seems to be necessary for bone induction. We suggest that at the interface of the implant and loose connective tissue this concentration is never reached, which results in maintenance of the rim.
Calcification and stress distribution in bovine pericardial heart valves
Authors: Berbacca G. M. , Fisher A. C. , Wilkinson R. , Mackay T. G. , Wheatley D. J. 
Published: May 2005

AbstractThere is a strong relationship between mechanical stress and calcification in biological prosthetic heart valves. A dynamic in vitro calcification test has been used to study the relationship between stress distributions in the leaflets of bovine pericardial valves and the deposition of calcium over the leaflet surfaces. Intuitive stress regions have been defined over the leaflet surfaces. Calcium uptake by the leaflets has been assayed directly by ashing of leaflet material and analysis of the ash by atomic absorption spectrophotometry. Calcium and phosphorus distribution over the leaflet surface has been analyzed using energy‐dispersive x‐ray analysis by scanning electron microscope and data points assigned to the appropriate stress region. The uptake of calcium is assessed by comparing stress regions, surfaces, and the degree of calcification of the valve. Differences between stress regions and surfaces are significant. Uptake of calcium in these valves appears to be strongly related to the degree and type of stress present in the valve leaflets.
Hydroxylapatite coating of porous implants improves bone ingrowth and interface attachment strength
Authors: Cook Stephen D. , Thomas Kevin A. , Delton Jeanette E. , Volkman Todd K. , Whitecloud Thomas S. , Key John F. 
Published: May 2005

AbstractThe effect of a plasma‐sprayed hydroxylapatite (HA) coating on the degree of bone ingrowth and interface shear attachment strength was investigated using a canine femoral transcortical implant modeI. Cylindrical implants were fabricated by sintering spherical Co‐Cr‐Mo particles 500–710 μm in diameter; the nominal implant dimensions were 5.95 ± 0.05 inm diameter by 18 mm in length. One half of each implant was coated with hydroxylapatite, 25–30 μm in thickness, by a plasma‐spray technique. Using strict aseptic technique, the implants were placed through both femoral cortices into defects approximately 0.05 mm undersized. After 2, 4, 6, 8, 12, 18, 26, and 52 weeks, the implants were harvested and subjected to mechanical pullout testing and undecalcified histologic evaluation. The application of the HA coating to porous implants enhanced both the amount of bone ingrowth and the interface attachment strength at all time periods. These differences were statistically significant for the percent of bone ingrowth at the 4‐, 6‐, 12‐, 18‐, 26‐, and 52‐ week time periods, and interface shear strength values were significantly different at the 6‐, 8‐, 12‐, 18‐, and 26‐week time periods. The rate of development of interface strength and bone ingrowth was also more rapid for the HA‐coated implants. No evidence of any disruption, mechanical failure, or biologic resorption of the HA coating was observed. The results of the present study‐demonstrating a beneficial effect of the HA coating at all time periods‐are believed to be due to the use of paired comparisons, which allow assessment of subtle differences that might otherwise have been obscured by normal biological variability.
Polyurethanes bearing pendant amino acids: Fibrinogen adsorption and coagulant properties
Authors: Santerre J. P. , ten Hove P. , Brash J. L. 
Published: May 2005

AbstractSegmented polyurethanes based on 4,4′‐ diphenylmethane diisocyanate and polypropylene oxide and chain extended with a sulfonated diamine were derivatized by reaction of sulfonate groups in the polymer with amino acids. The chemical composition of the derivatized polymers was determined by elemental analysis. Tensile stress–strain measurements indicated a slight increase in modulus and elongation with incorporation of amino acids. Water uptake at room temperature showed little change following derivatization, but at 70°C increased significantly. Water contact angles were not influenced by the presence of amino acids, but electron spectroscopy for chemical analysis data showed an increase in hard segment content in the near‐surface layers so that bulk and surface compositions were more nearly the same in the amino‐acid‐containing materials. Fibrinogen adsorption from plasma, shown previously to be high on the sulfonated polyurethanes, was reduced by derivatization, due probably to the decrease i n free sulfonate content. Thrombin times of plasma in contact with these materials were essentially the same for the derivatized and underivatized materials.
Synthesis of antibiotic‐loaded hydroxyapatite beads and in vitro drug release testing
Authors: Yamamura Keiko , Iwata Hisashi , Yotsuyanagi Toshihisa 
Published: May 2005

AbstractVarious forms of hydroxyapatite (HAP) materials have been developed for use as bone grafts. Since the risk of local infection is associated with surgery, it seems reasonable to incorporate drugs such as antibiotics into implant materials. We therefore investigated the characteristics of drug incorporation into a spherical porous HAP bead (diameter = 8.48 mm, bulk porosity = 0.439) and its in vitro release behavior. Cefotiam (CTM) was used as a model antibiotic. Because of nonuniform pore distribution in the bead, distribution of CTM was estimated from the amounts of CTM experimentally determined at three different sites: the surface, halfway to the center, and the center of the beads. The results indicated that 90% of the drug was incorporated in the concentric outer 0.387 (radius = 1) section of the bead. CTM was released with a short lag time when the dry HAP bead was placed in water. Incorporation of CTM with egg phosphatidylcholine eliminated initial lag time and decreased the release rate of the drug from the bead. The lipid load was useful in controlling the release of CTM from the beads. In addition, to protect relatively unstable drugs from humidity and avoid contamination of drug‐incorporated HAP beads an apparatus was designed with which the beads could be enclosed in vials in vacuo and under aseptic conditions on a bench‐scale basis.
Relations between in vitro cytotoxicity and crosslinked dermal sheep collagens
Authors: van Luyn M. J. A. , van Wachem P. B. , Olde Damink L. , Dijkstra P. J. , Feijen J. , Nieuwenhuis P. 
Published: May 2005

AbstractCollagen‐based biomaterials have found various applications in the biomedical field. However, collagen‐based biomaterials may induce cytotoxic effects. This study evaluated possible cytotoxic effects of (crosslinked) dermal sheep collagen (DSC) using a 7‐d‐methylcellulose cell culture with human skin fibroblasts. Non‐crosslinked DSC (NDSC), hexamethylene‐diisocyanate‐crosslinked DSC (HDSC), and glutaraldehyde‐crosslinked DSC (GDSC), their extracts (1 × 10 d to 4 × 10 d extracts), or the corresponding extracted DSC samples were tested. Cell growth was evaluated by cell counting, while cell morphology was assessed by light microscopy and transmission‐electron microscopy. Both GDSC and, to a lesser extent, HDSC, induced cytotoxicity, observed as inhibited cell growth and deviant cell morphology. The deviant morphology consisted of extensive accumulations of lipid, reduction in the amount and dilatation of rough endoplasmatic reticulum, increased inclusions of cell remnants, and relatively rounded cell membranes. With HDSC, both primary cytotoxicity, due to extractable products from the material, and secondary cytotoxicity, possibly due to a release of cytotoxic products resulting from enzymatic cell‐biomaterial interactions, could be discriminated. With GDSC, however, no clear distinction between primary and secondary cytotoxicity could be made. With NDSC, only primary cytotoxicity, measured as low inhibition of cell proliferation, but without deviant morphoIogy, was observed. These remarkable differences in cytotoxicity are discussed in relation to residual agents and specific crosslinks present i n DSCs as a consequence of processing and the crosslinking agents used. The residual agents and the specific crosslinks give rise to differ‐ ences in direct release of products and in sensitivity to hydrolysis and enzymatic breakdown.
Hemocompatibility of human whole blood on polymers with a phospholipid polar group and its mechanism
Authors: Ishihara Kazuhiko , Oshida Hiroko , Endo Yutaka , Ueda Tomoko , Watanabe Akihiko , Nakabayashi Nobuo 
Published: May 2005

AbstractThe hemocompatibility of a polymer containing a phospholipid polar group, poly(2‐methacryloyloxyethyl phosphorylcholine (MPC)‐co‐n‐butyl methacrylate(BMA)), with human whole blood was evaluated. When human whole blood without an anticoagulant was contacted with polymers, the blood cell adhesion and aggregation on the polymer without the MPC moiety was extensive, and considerable fibrin deposition was observed. This phenomenon was suppressed with an increase in the polymer MPC composition. Thus, the MPC moiety in the copolymer plays an important role in the nonthrombogenic behavior of the copolymer. These results were also confirmed by the whole blood coagulation time on the polymer surface which was determined by Lee‐White method. The adsorption of phospholipids and proteins from human plasma on poly(MPC‐co‐BMA) was investigated to clarify the mechanism of the nonthrombogenicity observed with the polymer. The amount of phospholipids was increased; whereas, adsorbed proteins were decreased with an increase in the MPC composition. From these results, we concluded that the phospholipids adsorbed on poly(MPC‐co‐BMA) play the most important role in the nonthrombogenicity of the MPC copolymer. © 1992 John Wiley & Sons, Inc.
In vitro and in vivo studies on bioabsorbable ultra‐high‐strength poly(L‐lactide) rods
Authors: Matsusue Yoshitaka , Yamamuro Takao , Oka Masanori , Shikinami Yasuo , Hyon Suong‐Hyu , Ikada Yoshito 
Published: May 2005

AbstractUltra‐high‐strength poly(L‐lactide) (PLLA) rods were fabricated using a drawing technique. Rods with a diameter of 3.2 mm and a draw ratio of 2.5:1 showed initial bending strength and modulus values of 240 MPa and 13 GPa, respectively. The purpose of this study was to investigate the in vitro and in vivo degradation of PLLA rods with a draw ratio of 2.5:1. The greater the rod diameter, the longer the bending strength was maintained in phosphate buffered saline at 37°C. The bending strength retention of rods (diam. 3.2 mm) implanted in the subcutis of rabbits was almost equal to that of rods in the in vitro study, while those rods implanted in the medullary cavity of rabbit femora showed a slightly lower bending strength retention. Molecular weight was reduced to the greatest extent in the medullary cavity, followed by in the subcutis and in vitro. The weight of PLLA rods in the medullary cavity was reduced by 22% at 52 weeks and by 70% at 78 weeks after implantation. Histologically, no inflammatory or foreign body reaction was observed in the medullary cavity for 52 weeks. The drawn PLLA rods maintained a bending strength exceeding that of human cortical bone in the medullary canal for a period of 8 weeks, suggesting that the drawn PLLA rods may be useful in the repair of fractured human bones. © 1992 John Wiley & Sons, Inc.
Mechanical deformation of polymer matrix controlled release devices modulates drug release
Authors: Edelman Elazer R. , Fiorino Anthony , Grodzinsky Alan , Langer Robert 
Published: May 2005

AbstractWhen magnetic fields were applied to polymer matrices of ethylene‐vinyl acetate copolymer embedded with drug and a small magnet, drug release was increased up to 30‐fold above baseline levels. It has been hypothesized that the effect of magnetic stimulation on the release of drugs from these matrices is the transduction of the applied magnetic field into a mechanical deformation of the matrix through motion of the magnet within the matrix. This current study provides support for this hypothesis by demonstrating that repeated pulsatile mechanical deformation of matrices can enhance the release of macromolecules from ethylenevinyl acetate copolymer matrices. Furthermore, similar modulated release kinetics were obtained with mechanically compressed and magnetically stimulated matrices. We also established that modulation was dependent on the ratio of compression area to matrix volume and that modulation was maximized when this ratio was optimized. © 1992 John Wiley & Sons, Inc.
Post‐plasma‐spraying heat treatment of the HA coating/Ti‐6Al‐4V implant system
Authors: Filiaggi M. J. , Pilliar R. M. , Coombs N. A. 
Published: May 2005

AbstractThe metal/ceramic interface that constitutes an important part of the plasma‐sprayed HA‐coated Ti‐6Al‐4V system may, in fact, represent the “weak link” in the implant design. A post‐plasma‐spray heat treatment to enhance chemical bonding at the metal/ceramic interface and, hence, improve the mechanical properties (interface fracture toughness and tensile coating adhesion strength) of the plasma‐sprayed implant system does show promise. In preliminary heat treatment studies, however, any improvements realized were lost due to the chemical instability of the coating in a moistureladen environment, with a concomitant loss in bonding properties. This deterioration in properties appears to be related to environmentally assisted crack growth as influenced by processing conditions. Still, an ability to improve HA/Ti‐6Al‐4V bonding through enhanced diffusion bonding was demonstrated, warranting further heat treatment studies involving atmosphere control during processing. © 1993 John Wiley & Sons, Inc.