bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and thrombogenicity of alkylated polyvinyl alcohol coated tubing
Authors: Strzinar Irena , Sefton Michael V.
Published: May 2005

A polyvinyl alcohol hydrogel (PVA) was reacted with a CI8 isocyanate at 80°C in dimethyl formamide (DMF) in order to improve the platelet reactivity of the hydrogel through an inf hence on albumin adsorption or retention. A C, isocyanate was used as a control. Surface coverage by XPS appeared to be ∼100% for both C4 and C18 modified surfaces, although the limited solubility of C18 isocyanate in DMF may have resulted in a nonuniform surface. Relative to PVA or the solvent treated control, octadecylation resulted in increased albumin adsorption (from a single protein solution) and increased retention when the adsorbed albumin was exposed to a fibrinogen solution. However, octadecylation did not obviate the platelet reactivity problem in preliminary studies: systemic platelet counts were reduced by about half over 4 days in a canine AV shunt experiment and the initial rate of platelet destruction for C IR‐PVA was greater (36%/ day) even than for the solvent‐treated PVA. Surprisingly in preliminary studies butylation of PVA resulted in little or no thrombocytopenia and did not appear to increase significantly the fractional rate of platelet destruction relative to the shunt only blank. It is presumed that the nonspecific effect of alkylation (independent of chain length) was the dominant contribution to the reduced platelet reactivity. A similar effect of C18‐PVA presumably would have been observed had the limited solubility of C18 isocyanate not precluded a uniform surface coverage.
A fractographic investigation of PMMA bone cenent focusing on the relationship between porosity reduction and increased fatigue life
Authors: James Susan P. , Jasty Murali , Davies Jefrey , Piehler Henry , Harris William H.
Published: May 2005

Fracture surfaces of both monotonic and fatigue loaded bone cement samples were examined to investigate the fractographic characteristics of PMMA. Classic cleavage step river patterns were observed on all monotonically loaded samples, running downstream in the direction of crack propagation. AH fatigue cracks initiated at internal pores and the direction of crack propagation of many cracks was discernible. Porosity, pore size, and pore size distribution were found to affect the crack initiation and fatigue behavior of bone cement. Statistical analysis revealed a strong negative correlation between twodimensional porosity present on the fracture surfaces and the cycles to failure. The fractographic observations of these fatigue samples elucidate one reason why porosity reduction by centrifugation or vacuum mixing increases the fatigue life of PMMA bone cement.
Measurement of the rate of thrombin production in human palsma in contact with different materials
Authors: Rollason Gordon , Sefton Michael V.
Published: May 2005

Thrombin 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

Biological 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

The 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

The 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

Allogeneic 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

There 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

The 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

Segmented 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

Various 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

Collagen‐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

The 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

Ultra‐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

When 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

The 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.
A critical evaluation of the purification of biominerals by hypochlorite treatment
Authors: Tomazic Branko B. , Brown Walter E. , Eanes Edward D.
Published: May 2005

The quantitative deproteination of calcific deposits from surgically explanted heart valve bioprostheses was carried out by both hypochlorite and hydrazine extraction to establish which is the better procedure for preparing purified mineral suitable for detailed chemical and structural characterization. Hypochlorite treatment resulted in a material with a higher Ca/PO4 ratio than that of the untreated deposits. The hydrazine treatment did not produce such an effect. A systematic comparison of x‐ray diffraction patterns of calcific deposits showed an increase in crystallinity of hypochlorite‐treated versus native material, while the crystallinity of hydrazine‐treated materials did not change. One other result of the hypochlorite treatment was a pronounced disaggregation of well‐ground calcific deposits into a particle populations ranging from 50–300 nm in size, as shown by scanning electron microscopy. Results comparable to the above findings were also obtained when the two treatments were applied to other bioapatites. On the other hand, mineral solubilities were comparable, regardless of which deprotenation treatment was used. The principal conclusion from this study is that hydrazine deproteination is preferable to hypochlorite extraction in isolating pathologic mineral deposits from bioprosthetic materials for further study. © 1993 John Wiley & Sons, Inc.
The functional equivalence of demineralized bone and tooth matrices in ectopic bone induction
Authors: Katz Ronald W. , Hollinger Jeffrey O. , Reddi A. H.
Published: May 2005

The objective of this study was to determine whether demineralized rat incisor matrices were a more potent inducer of ectopic endochondral bone formation than demineralized diaphyseal bone matrices derived from the same donors. Twenty‐five‐milligram disks of demineralized bone or tooth matrix obtained from adolescent Long‐Evans rats were implanted in a standardized ectopic site. Biochemical and histometric measurements of bone formation revealed that the two matrices were functionally equivalent inducers of endochondral bone formation. The induced pellicle of bone reached a maturation point 18 days after implantation. Dentin matrix implants generated a significantly greater amount of mineralized tissue than did bone matrix implants. This difference could be explained on the basis of remineralization of the dentin particles to a greater degree than the bone matrix particles. Initial observations suggesting a more robust osteoinductive activity in demineralized incisor matrix can be attributed to the decreasing activity of bone matrix from older donors when compared to younger donors. The extent of osteoinduction by the two substrata was equivalent when the matrices were matched for age. © 1993 John Wiley & Sons, Inc.
Ingrowth of bone into pores in titanium chambers implanted in rabbits: Effect of pore cross‐sectional shape in the presence of dynamic shear
Authors: Goodman Stuart , Toksvig‐Larsen Søren , Aspenberg Per
Published: May 2005

The micromotion chamber consists of a titanium outer cylinder and a central core, which are pierced by a transverse 1‐mm canal for tissue ingrowth. Six weeks after implantation in the proximal tibia in mature rabbits, the outer cylinder is osseointegrated; the central core can then be moved in relation to the fixed outer cylinder. Thus, the tissue growing through the pore, from the cylinder into the core, can be subjected to motion of a predetermined amplitude and frequency. In this study we investigate the influence of pore cross‐sectional shape on tissue ingrowth in the canal. In six animals, the outer cylinder was pierced by a square 1‐mm hole that was congruent with the square hole in the core; in five animals, the hole in the cylinder was round. The cross‐sectional area of the square hole in the cylinder was about 21% greater than in a round hole. In all cases, the channel in the inner core was a 1 × 1 × 5‐mm quadrate. All chambers underwent 20 cycles/day of micromotion for a 3‐week period. The amplitude of the micromotion was 0.5 mm. Chambers containing cylinders with a round hole demonstrated less bone ingrowth as compared to cylinders with a square hole. This observation may be due to several factors including the greater cross‐sectional area of the several factors including the greater cross‐sectional area of the square versus the round hole in the cylinder and the enhanced congruity provided by the square outer and inner holes, versus a round outer and square inner hole. © 1993 John Wiley & Sons, Inc.
Histological and biochemical evaluation of osteoblasts cultured on bioactive glass, hydroxylapatite, titanium alloy, and stainless steel
Authors: Vrouwenvelder W. C. A. , Groot C. G. , de Groot K.
Published: May 2005

We investigated the behavior of fetal rat osteoblasts cultured on four bone replacing materials: bioactive glass, hydroxylapatite, a titanium alloy, and stainless steel. The cultures were histologically examined for individual cell morphology and osteoblast expression after several periods of time using scanning electron, fluorescence, and normal light microscopy. Other cultures were used for biochemical determinations of alkaline phosphatase activity (APA) and DNA content. Osteoblasts cultured on bioactive glass showed a better osteoblast‐like morphology and a higher proliferation rate, leading to confluent cultures with higher cell density and a generally better expression of the osteoblast phenotype in comparison with the other substrates. The confluent bioactive glass cultures also showed significantly higher DNA content and APA as well as the calculated APA/DNA ratio. Based on the evaluation of histological and biochemical parameters we conclude that osteoblasts cultured on bioactive glass show a generally better osteoblast character than on the other materials. © 1993 John Wiley & Sons, Inc.
Attachment and proliferation of bovine aortic endothelial cells onto additive modified poly(ether urethane ureas)
Authors: Brunstedt Michael R. , Ziats Nicholas P. , Rose‐Caprara Veronica , Hiltner P. Anne , Anderson James M. , Lodoen Gary A. , Payet C. R.
Published: May 2005

To better understand endothelial cell interactions with poly(ether urethane urea) (PEUU) materials, and to assess bovine aortic endothelial cell attachment, films were incubated for 24 h with BAEC in media containing 5% fetal bovine serum. Other films were allowed to incubate for 4 more days in media containing 5% fetal bovine serum without cells to assess BAEC proliferation. The assay was performed on PEUU films modified with acrylate and methacrylate polymer and copolymer additives that spanned a wide range on the hydrophobicity/hydrophilicity scale. Tissue culture polystyrene (TCPS) was used as a control. The assay showed that PEUU films loaded with Methacrol 2138F [copoly(diisopropylaminoethyl methacrylate][DIPAM]/decyl methacrylate [DM]) (3/1) or with its hydrophilic component, DIPAM, in homopolymer form (i. e., h‐DIPAM), significantly enhanced BAEC attachment (∼80% of TCPS values) and proliferation (∼80%) when compared to unloaded PEUU films (attachment, 73%; proliferation, 47%) or to PEUU films loaded with the more hydrophobic acrylate or methacrylate polymer additives (attachment, 32–69%; proliferation, 18–57%). The assay also showed that PEUU films coated with homopoly(diisopropylaminoethyl acrylate) (h‐DIPAA) significantly enhanced BAEC attachment and proliferation when compared to PEUU films coated with h‐decyl acrylate (h‐DA); films coated with the copolymer of these two acrylates (i.e., co‐[DIPAA/DA] [3/1]) showed intermediate behavior. To explain the enhancement of BAEC interaction with films loaded with Methacrol 2138F or h‐DIPAM, when compared to unmodified PEUU films or to PEUU films loaded with more hydrophobic acrylate and methacrylate polymer additives, it was assumed that the additives near the surface region of the solvent swollen PEUU matrix may have migrated to, or near to, the PEUU‐air interface during film formation, creating an additive enriched PEUU surface region. It is suggested that, once at this surface region, dynamic reorientation in response to an aqueous medium ensured the additives were able significantly to influence protein adsorption, and concomitant endothelial cell behavior, but only if they interacted with aqueous media more favorably than the PEUU. The ability of Methacrol and h‐DIPAM additives to enhance endothelial cell behavior is argued to be the result of increased hydrophilicity. This is the result of exposed, hydrogen‐bonding DIPAM moieties and increased surface flexibility, which is itself due to the hydration of unhindered Methacrol chains, which may create an additive enriched PEUU‐water interfacial zone. © 1993 John Wiley & Sons, Inc.
Toxicity of L‐ascorbic acid to L929 fibroblast cultures: Relevance to biocompatibility testing of materials for use in wound management
Authors: Schmidt Richard J. , Chung Lip Yong , Andrews Andrea M. , Turner Terence D.
Published: May 2005

Fibroblast cultures are often used to evaluate materials intended for medical use, cytotoxicity being taken as an indicator of bioincompatibility. Such an approach has previously been taken with ascorbic acid in determining its value in wound healing. We have now reexamined the toxicity of L‐ascorbic acid to L929 fibroblast cells in culture. Concentrations of ascorbic acid between 0.5 mM and 11 mM were tested. At concentrations above 2 mM, ascorbic acid was found to inhibit cell proliferation, with cell viability decreasing as the concentration was increased. This effect could be prevented by the addition of either superoxide dismutase or catalase to the culture medium. Assays of glutathione and glutathione disulfide were carried out on 8 day old cultures exposed for 24 h to the same concentrations of ascorbic acid. A dose‐related depletion of glutathione occurred whilst glutathione disulfide levels remained essentially constant. Lactate dehydrogenase and glucose‐6‐phosphate dehydrogenase activities were induced by ascorbic acid at all concentrations tested but the ratio of NADP to NADPH nevertheless increased as the concentration of ascorbic acid increased. Finally, ATP in cells from 8‐day‐old cultures became depleted in the presence of ascorbic acid at concentrations in excess of about 5 mM when assayed after 24 h incubation. These biochemical changes and the concomitant cytostatic/cytotoxic effects may be ascribed to the reactive oxygen species produced by the autoxidation of ascorbic acid in the culture medium. Ascorbic acid breakdown products appeared not to be directly involved. In addition, our results suggested that superoxide acted cooperatively with hydroxyl to elicit these effects on the fibroblasts. It is evident from this study that the microenvironment surrounding fibroblasts in culture may differ fundamentally from that surrounding fibroblasts in a healing wound, making it impossible to extrapolate directly to an in vivo situation and hence to make any recommendations from these results concerning the use of ascorbic acid in wound healing. © 1993 John Wiley & Sons, Inc.
Comparison of bone–implant interface shear strength of solid hydroxyapatite and hydroxyapatite‐coated titanium implants
Authors: Hayashi K. , Inadome T. , Mashima T. , Sugioka Y.
Published: May 2005

The interface shear strength of uncoated Ti‐6Al‐4V, dense sintered hydroxyapatite (HA), and HA‐coated Ti‐6Al‐4V were compared. Interface shear strength was determined using a transcortical push‐out model in dogs 4 and 12 weeks after implantation. The interface shear strength of dense sintered HA and HA‐coated Ti‐6Al‐4V was significantly higher than that of uncoated Ti‐6Al‐4V (P < .001). There was no significant difference between the interface shear strength of dense sintered HA and HA‐coated Ti‐6Al‐4V. After the push‐out test for HA‐coated implants, the regions fractured at the bone‐coating interface and at the coating‐titanium interface coexisted at 4 weeks after implantation. At 12 weeks, the fracture site was, in all cases, the HA coating‐titanium interface, and, in a few samples, fractures inside the coating layer also were visible. © 1993 John Wiley & Sons, Inc.
Biotolerance of a semisolid hydrophobic biodegradable poly(ortho ester) for controlled drug delivery
Authors: Bernatchez Stéphanie F. , Merkli Alain , Tabatabay Cyrus , Gurny Robert , Zhao Qinghong H. , Anderson James M. , Heller Jorge
Published: May 2005

We evaluated the biotolerance of a new semisolid poly(ortho ester) (POE) intended for controlled drug delivery. Two different investigations were carried out in rats: subcutaneous injections and the cage‐implant system. Sodium hyaluronate (SH), 1%, in phosphate buffer was used as a noninflammatory control. When injected subcutaneously in rats, the POE induced a mild and local inflammation at 3 and 7 days followed by a minimal chronic inflammation at 14 and 21 days. When using the cage‐implant system, we quantified the inflammatory components of the exudate surrounding the implanted material within the cage system at 3, 7, 14, and 21 days. The total leukocyte and macrophage concentrations were higher only at 7 days for both SH and POE compared to the control (empty cage). The other parameters were not significantly different from the control. These results show that POE is well‐tolerated by rats when used subcutaneously. © 1993 John Wiley & Sons, Inc.
Integrin receptors and platelet adhesion to synthetic surfaces
Authors: Goodman Steven L. , Cooper Stuart L. , Albrecht Ralph M.
Published: May 2005

The activation‐independent and ‐dependent integrin receptors—glycoproteins GPIc–IIa (α5–β1) and GPIIb–IIIa (αIIb–β3)—are involved in platelet adhesion and thrombus growth on damaged subendothelium through interactions with fibrinogen, fibronectin, von Willebrand factor, and other adhesive proteins. Because these receptors are used in normal in vivo hemostatic adhesion, they may also have a role for adhesion onto synthetic surfaces in the vasculature. Platelet adhesion in vitro was examined onto Formvar, glass, and four polyurethaneureas with various soft segment chemistries and surface properties. Platelets were pretreated with RGD peptides before and after adhesion. RGD peptide pretreatment inhibited spreading and close contact formation compared to treatment with saline or control RGE peptides, with no observable effect on the number of adherent platelets per area. High‐voltage electron microscopy showed abnormally sparse and short microfilament structures with RGD peptide treatment, suggesting an indirect inhibition of actin filament formation. Video‐enhanced light microscopy showed a cessation of spreading and a partial reversal of close contacts following RGD peptide application to adherent platelets. Because minimal amounts of plasma proteins are present in column‐washed platelet suspensions, and as platelet secretion appeared to be minimal in these experiments, these observations suggest that RGD binding integrin receptors may function in platelet spreading even in the absence of exogenous ligand. As RGD peptides did not affect the numbers of adherent platelets, while producing substantial decreases in the extent of spreading, we suggest that platelet integrins, possibly GPIIb–IIIa, are involved in spreading on synthetic surfaces but not for initial adhesion. © 1993 John Wiley & Sons, Inc.
Mapping of glutaraldehyde‐treated bovine pericardium and tissue selection for bioprosthetic heart valves
Authors: Simionescu Dan , Simionescu Agneta , Deac Radu
Published: May 2005

Glutaraldehyde‐crosslinked bovine pericardium is widely used in bioprosthetic heart valve fabrication. In an attempt to set a scientific basis for more reproducible tissue selection, we produced and analyzed topographical maps of glutaraldehyde‐treated bovine pericardium. Whole pericardia were divided into specific anatomical areas and their thickness was measured and mapped on templates. In each area, the suture holding power was determined in both parallel and perpendicular (to the base‐apex line) directions; analyses of the tearing patterns in each fragment were used to evaluate predominant fiber orientation, and observations were confirmed by polarized light microscopy. Complete maps were superimposed graphically to aid in the selection of certain areas that would have known fiber orientation, high suture holding power, and suitable thickness. Our results describe regional heterogeneity of bovine pericardial structure and mechanical properties, specifically demonstrating variations in thickness, suture holding power, and collagen fiber orientation. Two areas of choice (representing about 35% of the total) were described as suitable for use in bioprosthetic heart valve fabrication. © 1993 John Wiley & Sons, Inc.
RINm5F cell culture on sephadex derivatives
Authors: Oturan N. , Serne H. , Reach G. , Jozefowicz M.
Published: May 2005

Interactions between polystyrene sodium sulfonate and insulin‐secreting RINm5F cells have been previously described. When cultured on these microcarriers, cells exhibited normal growth, altered morphology, and inhibition of the insulin secretion was observed. For the sake of comparison, interactions of RINm5F cells with Sephadex derivatives, namely, carboxymethyl Sephadex (CM Seph), benzylaminated CM Seph (CMB Seph), and sulfonated CMB Seph (CMBS Seph), as well Sephadex, were studied. Cells attached poorly and did not spread onto Sephadex and CM Seph microcarriers, but all other characteristics were normal. In contrast, with cells cultured on CMB Seph and CMBS Seph microcarriers cell attachment, morphology, and growth rate were comparable to those of cells grown on classic plastic wells. But, in the latter case, surprisingly, insulin secretion was enhanced. This effect is composition of the microcarriers dependent. The insulin secretion per cell‐microcarriers composition relationship suggests a specific interaction between an unknown membrane receptor of RINm5F cells and a composite ligand site made of a combination of different chemical functional groups present at the microcarriers surface. © 1993 John Wiley & Sons, Inc.
Time‐dependent changes in the mechanical properties of zirconia ceramic
Authors: Shimizu K. , Oka M. , Kumar P. , Kotoura Y. , Yamamuro T. , Makinouchi K. , Nakamura T.
Published: May 2005

Zirconia has received special attention, mainly because of its high strength and toughness. However, there is some controversy about the time‐dependent deterioration of its mechanical properties. To examine the change in mechanical properties of zirconia ceramics in vivo and in vitro, tetragonal zirconia polycrystal pieces were introduced into the medullary cavity of the tibia in Japanese rabbits and animals were sacrificed after 2, 4 and 6 weeks and 6, 12, and 30 mo, respectively. Alumina ceramic and hydroxyapatite (HAP) pieces were used as controls to investigate the differences in biocompatibility. Zirconia showed a bending strength of over 1000 MPa initially, and little time‐dependent change in strength was found in both in vivo environments. x‐Ray analysis showed little change in the transformation rate, i.e., less than 5 mol % in vivo and in vitro over a period of 3 years. To estimate time‐dependent changes in zirconia over a longer period, zirconia pieces were placed in 95°C saline solution for over 3 years and their mechanical properties examined at chosen intervals. No serious decrease of bending strength was found over the 3‐year period under these conditions. It is concluded that zirconia can be used clinically because it retains a bending strength of over 700 MPa under any experimental conditions for over 3 years. © 1993 John Wiley & Sons, Inc.
Hardness and young's modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel
Authors: Willems G. , Celis J. P. , Lambrechts P. , Braem M. , Vanherle G.
Published: May 2005

The recently developed nanoindentation technique was used to measure hardness and Young's modulus of small filler particles in resin composites and other dental restoratives. This technique eliminates the need to visualize indentations. Load and displacement are continuously monitored during a loading–unloading sequence, and hardness as well as Young's modulus are then calculated from the load–displacement curves taking into account the geometry of the indenter. Thirteen posterior composites, 3 dental ceramics for CAD/CAM restorations, 1 sintered porcelain, and 1 amalgam were investigated in this study. The results were compared to the hardness and Young's modulus determined by nanoindentation of human enamel. Of the dental materials tested, only five materials contain inorganic filler particles with a nanohardness not statistically different from that of enamel. The predominant fillers in all other materials, except amalgam and the prepolymerized resin fillers in Bell Firm PX, were found to be significantly harder. The dental restorative materials, except the alloy phase in amalgam, were composed of particles with a Young's modulus significantly lower than that of human enamel. The alloy phase in amalgam had a Young's modulus value comparable to that of enamel. © 1993 John Wiley & Sons, Inc.
Immobilization of high‐affinity heparin oligosaccharides to radiofrequency plasma‐modified polyethylene
Authors: Yuan Shengmei , Szakalas‐Gratzl Gyongyi , Ziats Nicholas P. , Jacobsen Donald W. , Kottke‐Marchant Kandice , Marchant Roger E.
Published: May 2005

Oligosaccharides of heparin with high affinity for antithrombin III (ATIII) have been immobilized onto surface‐modified NHLBI Primary Reference low density polyethylene (PE). PE was modified by radiofrequency plasma polymerized (<150 nm thick) films derived from N‐vinyl‐2‐pyrrolidone (PPNVP) or allyl alcohol (PPAA), and coupled by chemical derivatization to either 3‐aminopropyltriethoxysilane or amino‐terminated poly ethylene oxide). High affinity heparin oligosaccharides (HA‐heparin, anti‐factor Xa activity of 592 ± 120 IU/mg) prepared by partial deaminative cleavage of commercial crude heparin and fractionated by agarose‐ATIII affinity chromatography, were immobilized to surface‐modified PE by reductive amination. The anticoagulant activity, as determined by a chromogenic assay for the inhibition of factor Xa, was estimated to be 30–70 mIU/cm2, with binding estimated to be 56–119 ng/cm2. The highest activity was obtained for the HA‐heparin immobilized to PE modified by PPNVP with a PEO spacer. Visual confirmation of ATIII binding to immobilized HA‐heparin was demonstrated by a goldlabeled double antibody method with imaging by SEM. © 1993 John Wiley & Sons, Inc.