bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Polyurethane 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

The 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

Immobilized 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

The 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

Polyetherurethanes (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.
Peptide, protein, and cellular interactions with self‐assembled monolayer model surfaces
Authors: Margel S. , Vogler E. A. , Firment L. , Watt T. , Haynie S. , Sogah D. Y.
Published: December 2004

Model biomaterial surfaces with well defined chemistry were prepared from close‐packed alkyltrichlorosilane monolayers on polished silicon and glass. The outermost molecular groups which come in direct contact with the biological environment were varied across a wide range of oxidation states by employing CF3, CH3, CO2CH3, and CH2OH terminal functionalities. Characterization by contact angles, surface spectroscopy, and ellipsometry verified that these model surfaces could be repeatedly prepared with good consistency for routine use to study biomolecule adsorption onto model surfaces. Adhesion of canine endothelial cells and the adsorption of proteins (human serum albumin and human fibrinogen) as well as a series of synthetic defined oligopeptides to these model surfaces have been studied. Endothelial cells attachment and growth were in the rank order of: CH2OH > CO2Me > CH3 > CF3. The peptides were comprised of different alternating sequences of lysine, leucine, and tryptophan residues. These structural differences imparted different amphiphilic characters that led to measurable differences in the adsorption of these peptides to liquid‐vapor interfaces. The adsorption to model surfaces was studied using ESCA, radiometry, and concentration‐dependent contact angles. ESCA and radiometry measured irreversible biomolecules adsorption whereas the contact angle method measured steadystate adsorption. Radiometric results were inconsistent with ESCA, possibly due to artifacts associated with protein radiolabeling. © 1993 John Wiley & Sons, Inc.
Solution effects on the surface reactions of three bioactive glass compositions
Authors: Filgueiras M. Regina T. , La Torre Guy , Hench Larry L.
Published: December 2004

The in vitro five‐stage surface reactions of two bioactive glass compositions, 45S5 and 52S4.6, and one bioinert glass, 60S3.8, exposed to three simulated body fluids (SBF) were analyzed using Fourier Transform infrared Spectroscopy (FTIR). There was little effect of SBF composition on ion exchange, silica hydrolysis, and silica polymerization (stages 1–3) of glass with silica content up to 52 wt%. However, calcium and phosphate ions in SBF accelerated the formation of an amorphous calcium‐phosphate (a‐CP) layer (stage 4), and crystallization (stage 5) of the hydroxycarbonate apatite (HCAp) layer. The magnesium ions had a retardation effect on the kinetics of stages 4 and 5, but little effect on stages 1–3. In SBF solutions which contained calcium and phosphate ions an amorphous calcium‐phosphate (a‐CaP) layer formed on even a 60S3.8 glass which was not bioactive in vivo. However, the a‐CaP layer did not crystallize to form HCAp. Thus, there is a significant contribution from the ions present in the SBF solutions to the HCAP formation and crystallization of HCAp on bioactive glasses. Also, silanol repolymerization is necessary for rapid crystallization of HCAp. © 1993 John Wiley & Sons, Inc.
Structure and integrity of a plasma sprayed hydroxylapatite coating on titanium
Authors: Whitehead R. Y. , Lacefield W. R. , Lucas L. C.
Published: December 2004

Plasma sprayed hydroxylapatite (HA) coatings on titanium substrates were analyzed for process‐induced compositional and structural changes. The HA starting powder and the resulting HA coatings were characterized using x‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The integrity of the ceramic‐to‐substrate bond strength was also determined, by subjecting plasma sprayed HA coatings to shear/cantilever bond testing. The ceramic coatings retained the basic apatitic crystal structure of the starting powder; however, a considerable amount of amorphous material was created during the plasma spray process. FTIR and Raman spectroscopy revealed that the resulting coatings were partially dehydroxylated. Both XRD and FTIR spectroscopy results also suggested that amorphous material, as well as additional calcium phosphate phases such as α‐tricalcium phosphate (TCP) not in the starting powder, were present in the HA coating. Average bond strengths of the HA coatings to Ti were determined to be 14.8 MPa +/− 3.5, with fracture occurring at the interface and within the coating itself. © 1993 John Wiley & Sons, Inc.
Tissue reactions to subcutaneously implanted, surface‐modified silicones
Authors: Okada Toshiyuki , Ikada Yoshito
Published: December 2004

To evaluate the influence of surface properties on tissue reactions, the surface of a medical‐grade silicone elastomer was modified without changing the bulk properties. Surface modifications employed were oxidation by corona discharge in air, graft polymerization of watersoluble monomers, coating a polysaccharide through polyion complex formation, and covalent immobilization of cell‐adhesive proteins. Surface‐modified silicone sheets were implanted in the subcutaneous tissue of rats, and tissue reactions such as infiltration of inflammatory cells, appearance of foreign‐body giant cells, and collagenous capsule formation were studied. It was found that the thickness of collagenous capsules formed after 16 weeks' implantation was in the range of 85–95 μm for the nontreated ones and all the modified silicones except the acrylic acid‐grafted and the collagen‐immobilized silicones. © 1993 John Wiley & Sons, Inc.
In vivo corrosion of modular hip prosthesis components in mixed and similar metal combinations. The effect of crevice, stress, motion, and alloy coupling
Authors: Gilbert Jeremy L. , Buckley Christine A. , Jacobs Joshua J.
Published: December 2004

One hundred forty‐eight retrieved modular hip prostheses of both mixed (Ti‐6Al‐4V/CoCr) and similar (CoCr/CoCr) metal combinations were examined and positive evidence of corrosive attack was found in the conical taper region between head and stem. Significant corrosion was observed in both mixed and similar metal combinations with 16% of necks and 35% of heads (for mixed‐metal cases), and 14% of necks and 23% of heads (for similar‐metal cases) showing moderate to severe corrosive attack. There was a significant correlation between the percentage of prostheses with moderate to severe corrosion and the duration of implantation for both mixed and similar metal cases, indicating that this corrosion process is progressive in time. Moderate to severe corrosion was seen as early as 2.5 and 11 months (mixed and similar metals, respectively).

Scanning electron microscopy and x‐ray analysis identified several forms of corrosive attack in the cobaltbased component of the taper. These included, for both mixed and same metal combinations: preferential dissolution of cobalt, fretting, and pitting; mixed metals only: the formation of a Ti‐Cr‐Mo interfacial phase and interdendritic corrosion; and for similar metals: intergranular attack adjacent to grain boundaries enriched in molybdenum and silicon. It is hypothesized that the restricted crevice environment, coupled with high cyclic stresses which cause repeated fracture of the passive oxide films in the taper, result in an unstable electrochemical environment within the crevice for both the cobalt alloy and Ti‐alloy passive films. The passivity of these alloys is subsequently lost and active attack of the taper results. Also, the repeated fracturing of the passive films will result in large amounts of corrosion products being formed. This corrosion and particulate accumulation could result in loss of mechanical integrity of the implants in vivo, create particles for third body wear, and release particles into the surrounding tissues. © 1993 John Wiley & Sons, Inc.
Optimization of extruded collagen fibers for ACL reconstruction
Authors: Dunn Michael G. , Avasarala Prashanti N. , Zawadsky Joseph P.
Published: December 2004

Collagen fibers used in a scaffolding device for ligament reconstruction must be thin, strong, and degradable. The purpose of this study was to determine the effects of fiber diameter (20, 50, or 90 μm), crosslinking agent (uncrosslinked, dehydrothermal‐cyanamide, or glutaraldehyde), and hydration on the initial mechanical properties, biocompatibility, and subcutaneous degradation rates of fibers extruded from an acidic dispersion of insoluble type I collagen. The wet tensile strength of extruded collagen fibers was significantly improved by decreasing the fiber diameter. Lowdiameter, crosslinked fibers had wet tensile strengths ranging from 75–110 MPa. In contrast, high diameter fibers had wet strength values of about 30 MPa. The degradation rate of the implanted fibers, in contrast, was not significantly prolonged by changing the initial fiber diameter. This result is important because prolonged degradation of the fibers can lead to implant encapsulation instead of neoligament formation. By minimizing the diameter, fiber stregth can be increased without prolonging the fiber degradation rate. Low‐diameter, dehydrothermal‐cyanamide crosslinked fibers have greater tensile strength and a more rapid degradation rate than medium‐diameter, glutaraldehyde crosslinked fibers, and are therefore more suitable for use in a degradable ligament reconstruction device. © 1993 John Wiley & Sons, Inc.
The effect of phagocytosis of poly(L‐lactic acid) fragments on cellular morphology and viability
Authors: Lam K. H. , Schakenraad J. M. , Esselbrugge H. , Feijen J. , Nieuwenhuis P.
Published: December 2004

The aim of this study was to investigate the effect of phagocytosed poly(L‐lactic acid) particles on the morpholgy and viability of phagocytes, mainly macrophages. Therefore, predegraded poly(L‐lactic acid) (P‐PLLA) and nontreated PLLA (N‐PLLA) particles, both having diameters not exceeding 38 μm, were injected intraperitoneally in mice. P‐PLLA particles were obtained by 25 kGy γ‐irradiation of N‐PLLA particles. N‐PLLA and P‐PLLA particles were injected using an 0.3% ethanol/0.9% saline solution intraperitoneally to the mice. We also studied the release of the absorbed ethanol as a possible model for the release of low molecular weight, potentially toxic products. As control, nondegradable polytetrafluoroethylene (PTFE) particles and the carrier solution were used. After 1, 2, 3, 4, 5, and 7 days, the cells of the abdominal cavity were harvested to study the effect of phagocytosis of polymer particles on phagocytic cell morphology and viability. Studies with transmission electron microscopy indicated that, upon injection of particles in the peritoneal cavity, macrophages demonstrated signs of cell damage, cell death, and cell lysis due to phagocytosis of a large amount of P‐PLLA particles. The morphology of the cells that had phagocytosed the N‐PLLA and PTFE particles did not differ substantially from those of control animals in which only the solution was injected. Also, in the controls, hardly any cell death and no debris was observed. When the PLLA particles were injected as a suspension in a 0.3% ethanol/0.9% saline solution, no difference was observed between N‐PLLA and P‐PLLA. After phagocytosis, both cause cell damage, sometimes leading to cell death. The highest numbers of necrotic cells were observed on day 2. The effects could be caused by the (peak) release of degradation products from P‐PLLA fragments or by the release of the absorbed ethanol when the 0.3 ethanol/0.9 saline solution was used to administer the particles. In conclusion, it can be stated that cell damage, sometimes leading to cell death, may be caused by phagocytosed poly(L‐lactic acid) particles. © 1993 John Wiley & Sons, Inc.
Lack of inhibition of adhesion of an enteropathogenic Escherichia coli by polycarbophil
Authors: Mack David R. , Blain‐Nelson Penny L. , Mauger John W.
Published: December 2004

Anionic polyacrylic acid polymers, such as polycarbophil, have a number of properties that would make them suitable carriers for sustained antibiotic release formulations in the intestinal tract. However, little is known with regards to possible microbial adhesion to polycarbophil. The aim of this study was to evaluate for such an interaction using the rabbit enteric pathogen Escherichia coli RDEC‐1 (serotype 015:H‐). RDEC‐1 mediates attaching and effacing binding to intestinal epithelium in a manner morphologically identical to that observed in both human enteropathogenic E. coli and enterohemorrhagic E. coli infections. RDEC‐1 bacteria were grown to promote the expression of the mannose‐resistant AF/R1 adhesion pili. A nonpiliated mutant, strain M34, was used as a negative control. Using radioactive labeling of bacteria, we quantitated adhesion of piliated RDEC‐1 in the presence of polycarbophil using an in vitro adhesion assay system. Binding of piliated RDEC‐1 in the adhesion assay was greater than for nonpiliated M34 for all concentrations of bacteria greater than 109 (P < .05). Polycarbophil did not cause concentration‐dependent inhibition of piliated RDEC‐1 binding (P > .05). We conclude polycarbophi does not interfere with the AF/R1 adhesin ligand of RDEC‐1. Use of this polymer as a mucoadhesive drug delivery vehicle for nonabsorbable antibiotics in the treatment of gastrointestinal infections would not be expected to interfere with the protective effects of intestinal mucins. © 1993 John Wiley & Sons, Inc.
Cellular response to well‐characterized calcium phosphate coatings and titanium surfaces in vitro
Authors: Ong J. L. , Prince C. W. , Lucas L. C.
Published: December 2004

The cellular response to well‐characterized Ca‐P and Ti surfaces was analyzed. This study indicated that the ion‐beam sputtering process could produce a hydroxyapatite‐type coating. However, structural alterations such as the incorporation of CO3 and the loss of the OH groups were observed. The Ti surfaces were shown to be predominantly amorphous TiO2. The in vitro cell culture study showed no significant differences in cell number for the Ti and Ca‐P surfaces throughout the 12‐day study. Furthermore, the initial percentage of protein within the cell layers was significantly lower for cells on Ca‐P surfaces compared with the cell layer on Ti surfaces. However, after 3 h incubation, no significant difference in the percentage of protein was observed for the Ti and Ca‐P surfaces. © 1995 John Wiley & Sons, Inc.
Improvement of blood compatibility on cellulose dialysis membrane. III. Synthesis and performance of water‐soluble cellulose grafted with phospholipid polymer as coating material on cellulose dialysis membrane
Authors: Ishihara Kazuhiko , Miyazaki Hideki , Kurosaki Toshikazu , Nakabayashi Nobuo
Published: December 2004

To improve the surface blood compatibility on a cellulose hemodialysis membrane, a blood compatible polymer with a phospholipid polar group, poly[2‐methacryloyloxyethyl phosphorylcholine(MPC)], was immobilized on the surface through the coating of a water‐soluble cellulose grafted with poly(MPC) (MPC‐grafted cellulose, MGC). The MGC was synthesized by graft copolymerization of MPC on a water‐soluble cellulose using cerium ion as an initiator. The coating process on the cellulose membrane with and aqueous solution of the MGC was convenient, and the MGC on the surface was not significantly detached even after immersion in water. The permeability and mechanical strength of the membrane coated with the MGC did not decrease compared with the original membranes. The MGC‐coated cellulose membrane was blood compatible, as determined by the prevention of platelet adhesion and aggregation after contact with platelet‐rich plasma. From these results, it is concluded that the MGC may be a useful material for improving the blood compatibility of the cellulose hemodialysis membrane. © 1995 John Wiley & Sons, Inc.
Silicone breast implants: The role of immune system on capsular contracture formation
Authors: Granchi Donatella , Cavedagna Daniela , Ciapetti Gabriela , Stea Susanna , Schiavon Patrizia , Giuliani Renzo , Pizzoferrato Arturo
Published: December 2004

We evaluated the role of the immune system in the pathogenesis of the periprosthetic capsular contracture, the most frequently occurring complication following the implant of silicone prostheses. Peripheral blood samples from 22 patients with silicone‐gel‐filled implants were examined. In all cases a capsule was felt by palpation, and it was classified according to the Baker scale. Ten patients (group 1) had a Baker 2 contracture, and 12 (group 2) had severe contracture rated 3 and 4. The cells positive to antigens CD3, CD4, CD8, HLA‐DR, CD19, CD25, CD57, CD16, and CD14, and the cytotoxic activity of the lymphocytes on target cells K562 were assessed by cytofluorimetric analysis. At time 0 there were no statistically significant differences between patients and normal subjects, nor between the two groups. At 48 h, the group 2 patients had a number/mm3 of cells CD57 + significantly higher than both group 1 and control group (P < .05). In group 1 patients, the cytotoxic activity was similar to that of normal subjects, whereas in group 2 it was significantly increased, in respect to both the controls (P < .05) and group 1 (P < .001). In all groups, the contact of the lymphocytes with the silicone extract did not modify either the antigen expression or the lymphocyte functional activity. On the basis of these results we hypothesize the involvement of the immune system in the formation of the capsular contracture around the prosthesis. © 1995 John Wiley & Sons, Inc.
Nitric acid passivation of Ti6A14V reduces thickness of surface oxide layer and increases trace element release
Authors: Callen B. W. , Lowenberg B. F. , Lugowski S. , Sodhi R. N. S. , Davies J. E.
Published: December 2004

Passivation of Ti6Al4V and cpTi implants using methods based on the ASTM‐F86 nitric acid protocol are used with the intention of reducing their surface reactivity, and consequently the corrosion potential, in the highly corrosive biologic milieu. The ASTM‐F86 passivation protocol was originally developed for surgical implants made of stainless steel and chrome cobalt alloy. Using X‐ray photoelectron spectroscopy (XPS) to examine the effect of nitric acid passivation on the surface oxide layer of mill‐annealed Ti6Al4V and cpTi, we have found that such treatment actually reduced the oxide thickness on the alloy while having no significant effect on the pure metal. These results correlated with observations obtained using graphite furnace atomic absorption spectrophotometry (GFAAS) to detect trace element release from solid, mill‐annealed, Ti6Al4V and cpTi into serum‐containing culture medium. We detected significantly greater levels of Ti, Al, and V in the presence of passivated compared to nonpassivated Ti6Al4V. In contrast, nitric acid passivation did not influence Ti release from mill‐annealed Ti‐based metals, would indicate that re‐examination of ASTM‐F86‐based passivation protocols with respect to Ti6Al4V should be considered in view of the widespread use of this alloy for biomedical devices. © 1995 John Wiley & Sons, Inc.
Fracture toughness determination of dental materials by laboratory testing and finite element models
Authors: Pidaparti Ramana M. V. , Beatty Mark W.
Published: December 2004

This study assessed the effectivenness of finite element analysis in predicting the stress intensity factor (KIC) for three types of dental materials: a glass ionomer, a dental amalgam, and a composite resin. Laboratory tests were conducted on small single‐edge notch specimens loaded in three‐point bending to determine values for fracture toughness (KQ). Using the dimensions measured for each laboratory specimen, a J integral approach was employed to calculate KIC using finite element analysis. Both two‐dimensional plane strain and three‐dimensional models were used in determining KIC for each specimen, and these values were compared to the KQ values obtained from laboratory tests. The results indicated that no significant differences existed between laboratory results and those obtained from both two‐ and three‐dimensional finite element models (P > .85). For the three‐dimensional model, values for KIC were found to vary across the specimen thickness, with the values at the center of the specimen closely paralleling those obtained from the two‐dimensional plane strain J integral technique was as effective as the three‐dimensional technique in calculating values for KIC. © 1995 John Wiley & Sons, Inc.
Oxidative biodegradation mechanisms of biaxially strained poly(etherurethane urea) elastomers
Authors: Schubert Mark A. , Wiggins Michael J. , Schaefer Michael P. , Hiltner Anne , Anderson James M.
Published: December 2004

As part of ongoing studies in polyurethane biostability and biodegradation, we have investigated an in vitro system to test strained poly(etherurethane urea) (PEUU). Recently, we utilized this system to reproduce in vivo stress cracking in strained Pellethane®. In this study, strained PEUU was tested to determine whether it degrades through a common mechanism with Pellethane® and to further examine the steps involved in this degradation.

Biaxially strained PEUU elastomers were treated with an α2‐macroglobulin (α2‐Mac) protein solution followed by an oxidative H2O2/CoCl2 treatment. Characterization of the strained PEUU specimens was performed with attenuated total reflectance‐Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), electron spectroscopy for chemical analysis, and contact angle analysis. The results from these characterization techniques provide conclusive evidence that biodegradation of PEUU and Pellethane® occurs through a common mechanism. Chemical changes to the PEUU include cleavage of the polyether soft segments and urethane linkages, leaving the hard segment domains unaffected. SEM analysis shows that this chain cleavage leads to the development of severe pitting and cracking of the PEUU surface. In addition, the in vitro degradation accurately reproduces the in vivo degradation chemically and physically. This result verifies that the primary species responsible for biodegradation of PEUUs, in vivo, are hydroxyl and/or hydroperoxide radicals. α2‐Mac pretreatment increases the rate of degradation compared to direct treatment in H2O2/CoCl2. As the PEUU soft segment chains are cleaved, the degradation products are extracted into the treatment solution or environment. Finally, a new biodegradation mechanism of PEUUs is presented that involves crosslinking of the polyether soft segments. © 1995 John Wiley & Sons, Inc.
Bioactive material template for in vitro, synthesis of bone
Authors: El‐Ghannam Ahmed , Ducheyne Paul , Shapiro Irving M.
Published: December 2004

We describe the synthesis of a new, porous, modified bioactive glass for use as a template for bone formation in vitro. The porosity of the glass was 36.4%; the pore size ranged from 10–160 mm, and there was no incipient devitrification. Prior to seeding the glass with cells, it was necessary to condition the disks. Optimum conditioning was achieved by immersing the templates in a tris buffer at pH 6.8 for 48 h and then treating the glass with tissue culture medium for 1 h at 37°C. The conditioned glass disks were seeded with 106 neonatal rat calvaria osteoblast‐like cells; cells on the substrate were maintained in culture for 3–7 days. To prevent pH shifts due to corrosion of the conditioned glass, the medium:glass ratio was maintained at 90 ml/g. We found that the templates were rapidly invaded by cells which maintained the osteoblast phenotype; thus, they exhibited high alkaline phosphatase activity and synthesized type I collagen and osteocalcin. SEM‐EDAX showed that the cells elaborated substantial amounts of extracellular matrix and a bonelike tissue was present throughout the entire template thickness. FTIR analysis of material formed in the glass indicated that the mineral phase was a biologic hydroxyapatite. Controls (cells without substrate and substrate without cells) exhibited none of these features. Results of the study suggest that this porous glass can function as a template for generating bone in vitro. © 1995 John Wiley & Sons, Inc.
Computer‐Assisted three‐dimensional reconstruction of epithelial cells attached to percutaneous implants
Authors: Chehroudi B. , Soorany E. , Black N. , Weston L. , Brunette D. M.
Published: December 2004

It is generally accepted that cell shape plays a pivotal role in many aspects of cell behavior including proliferation, differentiation, and gene expression. Although previous reports have shown that implant‐surface topography can alter cell shape in vitro, in vivo evidence for such an effect is largely based on intuitive interpretation of two‐dimensional histological sections. The objective of this in vivo, study was to develop a method to reconstruct in three dimensions the shape of epithelial cells attached to smooth and micromachined implant surfaces. Titanium‐coated epoxy replicas of smooth and 10‐μm‐deep micromachined grooved surfaces were implanted percutaneously in the parietal of region of rats. After 7 days the implants and attached tissue were removed and processed for light and electron microscopy. One‐micrometer‐thick serial histological sections were used to trace and digitize cells and their nuclei into a Hewlett Packard computer. Three‐dimensional images were reconstructed and rotated to measure length, width, height, area, orientation index and the angle cells or nuclei formed with the long axis of the grooves (XY angle), and the angle cells or nuclei formed with the long axis of the implant (XZ angle). Epithelial cells attached to the smooth surfaces were found to be significantly (P, < .05) flatter and more spread than were the cells attached to the grooved surfaces. Cells on the smooth surfaces were aligned parallel with the long axis of the implant, whereas on the grooved surfaces cells were oriented obliquely with the implant. There was a strong correlation (r = 0.9) between measurements of parameters of cells and those of nuclei on the smooth surfaces, but little correlation was found for the cells and their nuclei on grooved surfaces. These measurements indicated that cell shape is altered by the topography of the implant surface in vivo, but that one cannot necessarily predict the shape of a cell from the shape of its nucleus. © 1995 John Wiley & Sons, Inc.
Glass Wool–H2O2/CoCl2 test system for in vitro evaluation of biodegradative stress cracking in polyurethane elastomers
Authors: Zhao Qinghong , Casas‐Bejar Jesus , Urbanski Peter , Stokes Ken
Published: December 2004

Environmental stress cracking (ESC) in polyetherurethanes has been demonstrated in animal models. However, duplication of this phenomenon in vitro has been a challenge. The glass wool‐H2O2/CoCl2 test system was designed to provide oxidation components found in vivo, i.e., hydroxyl radical (HO·), molecular oxygen (O2), and superoxide (O) required for auto‐oxidation of polyetherurethanes. The in vitro test is not only reliable in duplicating the characteristics of in vivo stress cracking in polyetherurethanes at 37°C, but also accelerates ESC as much as seven times. The test results on several types of polyurethanes showed that Tecothane 80A was as vulnerable to biodegradative stress cracking in vitro as Pellethane 2363‐80A, while the new generation of polyurethanes, Corethane, demonstrated great resistance against stress cracking. © 1995 John Wiley & Sons, Inc.
Mediator interactions in macrophage/particulate bone resorption
Authors: Horowitz Stephen M. , Purdon Marie A.
Published: December 2004

The purpose of this study was to examine the mechanism by which mediators released from macrophages exposed to cement particles may interact with cells in bone to ultimately lead to bone resorption. Macrophages were exposed to cement particles, and then this conditioned medium was exposed to rat calvarial bones in vitro. The macrophage conditioned medium contained increased levels of tumor necrosis factor, but not interleukin 1 or prostaglandin E2. Exposure of this medium to the calvaria led to release of prostaglandin E2 by the calvaria, but not tumor necrosis factor or interleukin 1. Bone resorption was assessed by measuring the release of calcium 45 from the newborn rat calvarial bones. At 48, 72, and 96 h of incubation, the macrophage/cement particle‐conditioned medium led to the release of both prostaglandin E2 and calcium 45 from the calvaria. To determine whether the release of calcium 45 was dependent on prostaglandin E2 production by the cells in bone, the calvaria were incubated with 600 ng/ml of indomethancin in addition to the macrophage‐conditioned medium. The addition of indomethacin was effective in inhibiting both prostaglandin E2 and calcium 45 release from the calvaria, even after 96 h of exposure to the macrophage‐conditioned medium. This study suggests that tumor necrosis factor produced in association with macrophage/cement particle osteolysis arises from macrophages and not cells in bone, and that prostaglandin E2 originates from cells in bone and not from macrophages. Interleukin 1 was not found to be produced by macrophages or bone, and appears to have a lesser role. This study also suggests that the production of prostaglandin E2 by cells in bone plays an important role in the bone resorption which accompanies aseptic loosening. Macrophage exposure to bone‐cement particles leads to the release of mediators which stimulates bone resorption, at least in part, through a prostaglandin E2‐dependent mechanism. © 1995 John Wiley & Sons, Inc.
Creep characteristics of hand‐ and vacuum‐mixed acrylic bone cement at elevated stress levels
Authors: Norman T. L. , Kish V. , Blaha J. D. , Gruen T. A. , Hustosky K.
Published: December 2004

Compressive creep testing of cylindrical specimens machined from two commercial self‐polymerizing acrylic bone cements demonstrated measurable creep strains with higher creep strains for the hand‐mixed cement specimens compared to vacuum‐mixed cement ones. The average creep strains of hand‐mixed cement, after 6 h of constant load, ranged from 0.11° at 10.5 MPa to 14.0° at 50 MPa of applied stress. Vacuum mixing reduced the average creep strain to 6.7° after 6 h of applied stress at 50 MPa. There were no significant differences in the creep response between the two types of acrylic cements. The difference in creep resistance of the two cements was reduced after vacuum mixing (P = .013), which also significantly reduced the cement's internal porosity. © 1995 John Wiley & Sons, Inc.
Characterization of nodules induced by bioactive glass on cultured periodontal‐ligament fibroblasts
Authors: Kubo Kohji , Kamada Tetsuro , Matsuyama Takashi , Tsukasa Nobuyuki , Uehara Mayumi , Izumi Yuichi , Kitano Motoo , Ogino Makoto , Sueda Takeshi
Published: December 2004

We previously reported that materials leached from bioactive glass (BG) and vitamin D3 induced the formation of nodules on cultured periodontal‐ligament fibroblasts (PLF). In this study, we have investigated the relationship between the conditions of the materials and nodule formation, analyzed morphologically, and also studied whether the production of nodules was specific to cultured PLF. PLF and skin fibroblasts were cultured in the presence or absence of BG. The amounts of calcium, phosphate, sodium and silicon in the culture medium and the number of nodules were measured at the 55th day. The nodules were observed microscopically and analyzed using an X‐ray microanalyzer. In PLF, nodules were formed regardless of the presence or absence of BG; however, they were more numerous in the presence of BG. In skin fibroblasts, nodules were not observed. The amounts of calcium and silicon were higher in the presence of BG, while the amount of phosphate was lower. The nodules appeared crystalline with a spongy structure and contained calcium and phosphorus. Our results show that the nodules were associated with PLF and precipitated by the materials (higher concentrations of calcium and silicon), and they were spongy crystal composed of calcium and phosphorus. © 1995 John Wiley & Sons, Inc.
Cranial bone apposition and ingrowth in a porous nickel–titanium implant
Authors: Simske S. J. , Sachdeva R.
Published: December 2004

A 5 × 5 × 1‐mm uncoated porous nickel‐titanium (nitinol) implant was placed 4 mm to either side of the midsection of the frontal bone and 4 mm anterior to the coronal suture of the cranial bone of New Zealand White rabbits. In the other frontal location, a 5 × 5 × 1‐mm coralline hydroxyapatite (HA) (Interpore 200, a well‐known craniofacial implant material) implant was fitted. Rabbits were killed at each of three postsurgical intervals (2, 6, and 12 weeks), and the implants were evaluated for gross biocompatibility, bony contact, and ingrowth. No adjacent macrophage cells were observed for either implant type, and overlaying soft tissues and connective tissues readily adhered to the implants even after 2 weeks. Both materials made bone contact with the surrounding cranial hard tissue, and percent ingrowth increased with surgical recovery time. Measurements of microhardness and bone histologic parameters indicated that bone in contact with and grown into the implants was similar in properties to the surrounding cranial bone. Porous nitinol implants therefore appear to allow for significant cranial bone ingrowth after as few as 12 weeks, and thus nitinol appears to be suitable for craniofacial applications. Compared to HA, the nitinol implants demonstrated a trend for less total apposition and more total ingrowth after 6 and 12 weeks of implantation. © 1995 John Wiley & Sons, Inc.
Preservation of surface‐dependent properties of viral antigens following immobilization on particulate ceramic delivery vehicles
Authors: Kossovsky Nir , Gelman Andrew , Sponsler Edward , Rajguru Samir , Torres Mariel , Mena Ed , Ly Khan , Festekjian Ara
Published: December 2004

B‐cell stimulation for the purpose of evoking an effective neutralizing humoral immune response is a surface phenomenon that is exquisitely specific to antigen conformation. Consequently, successful delivery of antigen, such as would be desired in a vaccine, entails preservation of an antigen's apparent native surface (conformational) properties. Prior to testing the actual vaccinating efficacy of delivered antigens, the surface properties could be assessed through a variety of in vitro and in vivo assays in which the measurement standard would be the properties of the antigens in their native state (whole virus). Using surface modified nanocrystalline carbon and calcium‐phosphate ceramic particulates (carbon ceramics and brushite), we evaluated the surface activity of immobilized non‐nuclear material extracted from HIV‐1. Physical characterization showed that the particles with immobilized antigen („HIV decoys”︁) measured 50 nm in diameter (HIV = 50–100 nm) and exhibited the same ξ potentials as whole (live) HIV. In vitro testing showed that the HIV decoys were recognized by both conformationally nonspecific and specific monoclonal antibodies, were recognized by human IgG from HIV antibody‐positive patients, and could promote surface agglomeration among malignant T‐cells similar to live HIV. Last, in vivo testing in three vaccinated animal species showed that the HIV decoys elicited humoral and cellular immune responses similar to that evoked by whole (live) HIV. © 1995 John Wiley & Sons, Inc.
Assessment of viability and proliferation of in vivo silicone‐primed lymphocytes after in vitro re‐exposure to silicone
Authors: Ciapetti Gabriela , Granchi Donatella , Stea Susanna , Cenni Elisabetta , Schiavon Patrizia , Giuliani Renzo , Pizzoferrato Arturo
Published: December 2004

The functional response of peripheral blood lymphocytes isolated from 22 patients with silicone gel‐filled breast implants was assessed after in vitro re‐exposure to silicone. Using cell culture test methods to quantify proliferation and viability and/or activation of lymphocyte microcultures, i.e., the uptake of tritiated thymidine (3H‐TdR uptake test) and the reduction of formazan salts (MTT assay), interesting data were obtained. Peripheral blood lymphocytes purified from patients wearing silicone gel‐filled breast implants react in vitro to silicone showing a statistically significant increase of both proliferation and viability, while healthy subjects do not respond on in vitro exposure to silicone. Differences resulted even more statistically significant when patients were divided into two groups depending on the type of surgery they underwent: patients with breast augmentation for aesthetic reasons seem to have an increased responsiveness in vitro to silicone compared to patients who experienced a reconstructive surgery of the breast. Although they are still preliminary, being referred to a limited population, these results suggest that the lymphocytes of patients with silicone gel‐filled breast implants could be sensitized in vivo toward silicone; the re‐exposure of these cells to silicone leads to a higher functional response which could be looked for by using quantitative in vitro test methods. © 1995 John Wiley & Sons, Inc.
Role of cyclic plastic deformation in the wear of UHMWPE acetabular cups
Authors: Wang A. , Stark C. , Dumbleton J. H.
Published: December 2004

The mechanisms of wear in ultra‐high‐molecular‐weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator‐tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet‐like flakes from initial machining marks, and the other by the formation of fine ripples and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations. © 1995 John Wiley & Sons, Inc.
Hydroxyapatite‐clay bone fixation for loaded implants
Authors: Maruyama Masaaki
Published: December 2004

A clay containing hydroxyapatite (HA clay), which was made by mixing HA granules (range of sizes: 0.1–0.3 mm) and a saline solution of sodium alginate, was inserted into the medullary canal of an osteotomized rabbit's tibia with a Ti‐6Al‐4V titanium alloy implant. Each implant had a conical portion for bearing load. The shear strength of the bone‐implant interface for the implant with HA clay was significantly greater than that for the implant without HA clay 3 months postoperatively (P < .02), while there was no significant difference between the two strengths 1 week postoperatively. Under microscopic observation, the percentage of area of newly developed bone was also significantly greater for the implant with HA clay than for the implant without HA clay 3 months postoperatively (P < .04). This study suggests that HA clay encouraged adequate bone fixation of the loaded implant in 3 months, while the clay was not effective for immediate fixation. © 1995 John Wiley & Sons, Inc.
Bovine serum albumin conformation on methyl and amine functionalized surfaces compared by scanning force microscopy
Authors: Taborelli M. , Eng L. , Descouts P. , Ranieri J. P. , Bellamkonda R. , Aebischer P.
Published: December 2004

We investigated the adsorption of albumin on chemically modified gold surfaces by scanning force microscopy operating both in contact and noncontact mode. The surface modification was performed with thiol‐based selfassembling molecules carrying amine or methyl groups. The albumin on the aminoethanethiol‐coated gold formed a uniform layer and single molecules could be distinguished. On the dodecanethiol‐coated surface the protein adsorbed in aggregates or single isolated molecules depending on the incubation time. The width of the albumin molecule on both surfaces was similar, but the height was much lower on the amine than on the methyl surface. This was interpreted as a difference in the conformation of albumin depending on the substrate, and could explain the promotion of cell adhesion on amine‐treated polymers coated with albumin. © 1995 John Wiley & Sons, Inc.