bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of pore size and endothelial cell seeding upon the performance of small‐diameter e‐PTFE vascular grafts under controlled flow conditions
Authors: Boyd Kevin L. , Schmidt Steven , Pippert Todd R. , Hite Scott A. , Sharp William V. 
Published: December 2004

AbstractThe purpose of this study was to determine the effects of endothelial cell seeding and graft internodal distance upon the performance of 4‐mm‐ID e‐PTFE grafts during acute reduced blood flow conditions. PTFE grafts especially manufactured with three different mean internodal distances (28, 40, and 52 μm) were evaluated. Fifteen dogs (n = 5 for each design of PTFE graft) underwent bilateral carotid artery replacements with 6 cm lengths of 4‐mm‐ID PTFE grafts. In each dog one graft was seeded with enzymatically derived endothelial cells; the contralateral graft was nonseeded. All grafts were evaluated 5 weeks postoperatively. Dogs with bilaterally patent grafts were subsequently subjected to flow conditions through the graft that were maintained at 30% of the initial flow rates for 4 hr. Following controlled low flows the grafts were excised and assessed for patency, thrombus‐free surface area, inner capsule thickness and prostacyclin production. Endothelial cell seeding of these small‐diameter e‐PTFE vascular grafts improved patency and thrombus‐free surface areas in grafts of all pore sizes, with these parameters being greatest in the 40‐μm grafts. Inner‐capsule healing in these grafts was controlled and related to the pore size. PGI2 production was improved in endothelial cell seeded grafts of all pore sizes. However, neither endothelial cell seeding nor graft pore size affected the performance of these e‐PTFE grafts under conditions of reduced blood flows.
Calcium phosphate‐coated porous titanium implants for enhanced skeletal fixation
Authors: Rivero D. P. , Fox J. , Skipor A. K. , Urban R. M. , Galante J. O. 
Published: December 2004

AbstractPorous titanium fiber implants for cementless skeletal fixation by bone ingrowth were treated with a calcium phosphate coating applied by a plasma flame‐spray technique. In a paired experiment, treated and control implants were inserted in the humeri and olecranons of 36 adult dogs for periods of 1, 2, 4, and 6 weeks. After the animals were sacrificed, a biomechanical evaluation of the strength of skeletal fixation of the implants and a histologic evaluation of bone ingrowth was done. The mean shear strength of skeletal fixation at four weeks for the calcium phosphate‐coated implants was 24% greater (p < .01) than for paired controls. No difference in strength of fixation between treated and control implants was present at other time periods. The osteoconductive properties of the ceramic coating were demonstrated by bone forming in direct contact with the calcium phosphate coating on the metal fibers of the treated implants. No significant increase for the volume of bone ingrowth was established for treated implants compared to paired controls at any time period.
Cell morphology, proliferation and collagen synthesis of human fibroblasts cultured on sepiolite–collagen complexes
Authors: Olmo Nieves , Lizarbe Maria A. , Turnay Javier , Müller Klaus P. , Gavilanes José G. 
Published: December 2004

AbstractThe growth and morphology as well as collagen biosynthesis of human fibroblasts obtained and cultured on sepiolite–collagen complexes have been studied. No differences on cell morphology and growth properties nor collagen synthesis were observed when compared with standard culture substrates. The type I/type III ratio of biosynthesized collagen by fibroblasts cultured on sepiolite–collagen complexes was about 5–6 with no difference when compared to control conditions. This normal behavior was also observed for the type I/type III procollagens. According to these studies the sepiolite–collagen complexes do not modify the studied features of the fibroblasts.
Endothelialization of polymer surfaces
Authors: Absolom D. R. , Hawthorn L. A. , Chang G. 
Published: December 2004

AbstractThe role that substrate surface properties play in influencing the extent of endothelialization of polymer surfaces has been investigated. For a wide range of polymer surfaces, the degree of endothelialization cells is directly related to polymer surface tension: increased endothelialization occurring with increasing substrate surface tension. As a result of adsorption of the proteins in the culture media, the surface properties of the polymers are altered considerably. The protein‐coated polymers were characterized by means of liquid–liquid contact angle measurements under non‐denaturing conditions. A striking correlation is observed between the degree of endothelialization and the measured dextran contact angle. The degree of endothelial cell spreading is not related to polymer surface tension. Cell morphology and extracellular matrix production, however, are influenced by substrate surface properties.
Cellular morphology and distribution on a stretching blood–material interface
Authors: McMillin Carl R. , Malladi Madhusudan R. , Ott Donald W. , Evancho Michelle M. , Schmidt Steven P. 
Published: December 2004

AbstractIn order to investigate the interactions of cellular elements and protein on constantly deforming (fatiguing) blood contact surfaces, a series of ex vivo canine arteriovenous shunt experiments were conducted. While fresh blood was flowing through Silastic tubing shunts, portions of the tubing were stretched 20 to 60% at a frequency of 20 to 90 cycles per minute for 10 to 90 min. The surfaces of the tubing that were stretched were compared with control tubing surfaces taken from the arterial side of the test segment using scanning electron microscopy and interference phase contrast microscopy.Approximately the same number of platelets were deposited on the stretched as on the unstretched portions of the tubing in the ten minute experiments. On the control portions of the tubing, the platelets were deposited singly and uniformly in what appeared to be a fairly inactivated state. On the stretched tubing, more pseudopod extension and aggregation was observed. In these preliminary experiments, no differences were noted as a function of frequency of stretch. As the blood contact time and the percent stretch were increased, only nonuniform, scattered aggregations of platelets, and platelets mingled with fibrin were seen. Significant numbers of spread white blood cells were observed on many of the segments of Silastic tubing stretched 20% for as short a time as 15 min. Granulocytes have occasionally been reported on less hemocompatible biomaterials after exposure to canine blood. This helps to confirm that substrate stretching of 20–60% had an adverse effect on the blood compatibility of the Siliastic tubing.
Estimation of surface‐bound heparin activity: A comparison of methods
Authors: Chandler W. L. , Solomon D. D. , Hu C. B. , Schmer G. 
Published: December 2004

AbstractWe compared two assays for estimating the amount of active heparin bound to a catheter surface: (1) a kinetic assay based on the inactivation of thrombin by antithrombin III, and (2) thrombin uptake. Both assays were used to estimate the amount of heparin activity on a series of catheters coated with no heparin, covalently bound heparin, and ionically bound heparin. The kinetic assay produced estimates of surface‐bound heparin activity and showed that some binding methods resulted in destruction of most of the heparin's biologic activity. In contrast, the thrombin uptake assay did not correlate with the amount of heparin activity on the catheter surface. Substantial thrombin uptake was found on surfaces coated with no heparin or inactive heparin, while low thrombin uptake was found on surfaces with high levels of heparin activity in the kinetic assay. We conclude that: (1) a kinetic assay based on the heparin accelerated inactivation of thrombin by antithrombin III can be used to estimate the amount of active heparin bound to a catheter surface, and (2) thrombin uptake studies do not correlate with heparin activity and do not predict which heparin binding method will result in the highest concentration of active heparin on the catheter surface.
Separation of B‐ and T‐lymphocytes by cellular adsorption chromatography using poly(2‐hydroxyethyl methacrylate)/polyamine graft copolymer as column adsorbent
Authors: Maruyama A. , Tsuruta T. , Kataoka K. , Sakurai Y. 
Published: December 2004

AbstractA series of poly(2‐hydroxyethyl methacrylate)/polyamine graft copolymers (HA copolymers) were examined as an adsorbent for cellular adsorption chromatography in order to separate cell populations with high efficacy. The capability of each copolymer sample to selectively adsorb rat lymphocyte subpopulations (B‐cells and T‐cells) was evaluated by applying a lymphocyte suspension to a copolymer‐coated glass bead column. A separation factor (AB/AT) greater than 5.0 was achieved for the HA copolymer, compared to 1.9 and 1.1 for homopolymers of poly(2‐hydroxyethyl methacrylate) and of a polyamine (poly(N,N‐diethylaminoethylstyrene)), respectively. By loading a rat lymphocyte suspension containing B‐cells (28%) and T‐cells (72%) through the HA copolymer column, more than 60% of T‐cells in 90% purity or more were recovered in the effluent.
Thermomechanical study of Ni‐Ti alloys
Authors: Lee J. H. , Park J. B. , Andreasen G. F. , Lakes R. S. 
Published: December 2004

AbstractA preliminary study was conducted to demonstrate the usefulness of the combined technique of differential scanning calorimetry (DSC) and mechanical testing for the shape memory metals of 54NiTi and 53NiTiCo(3%) alloys. The DSC technique was used to measure precise transformation temperatures and the amount of thermal energy required for the corresponding phase transformation. The degree of plastic deformation by bending and the effect of alloying (such as Co) were studied with combined DSC and mechanical property measurements.
The study of thermal and gross morphologic properties of polyglycolic acid upon annealing and degradation treatments
Authors: Chu C. C. , Browning A. 
Published: December 2004

AbstractThe objective of this study is to alter the fiber morphology of a linear aliphatic polyester, polyglycolic acid, by annealing treatment and to examine the changes of its degradation properties. The annealing was done at 150°C, 170°C, and 190°C, and the specimens were annealed in four different strained conditions, freely hung, 0, 1, and 10%. After annealing treatments, the specimens were subject to in vitro hydrolytic degradation by immersing them in phosphate‐buffer solution of pH 7.4 at 37°C for up to 28 days. The thermal properties and gross morphology of the specimens were obtained. It was found that annealing treatments resulted in initial higher levels of crystallinity, which, in turn, influenced the hydrolytic degradation of the fiber. Among all the annealing conditions, the freely hung specimens annealed at 190°C exhibited the most pronounced annealing effect on hydrolytic degradation, and was consistent with the observed gross morphologic changes. The change in the characteristics of fiber structure (i.e., the return to the stage of less oriented conformation upon freely hung annealing) was thought to be the cause.
Effect of delay between tissue harvest and glutaraldehyde pretreatment on mineralization of bovine pericardium used in bioprosthetic heart valves
Authors: Maranto Anthony R. , Schoen Frederick J. 
Published: December 2004

AbstractThere is concern that delayed glutaraldehyde treatment of bioprosthetic tissue could potentiate calcification by autolytic generation of mineralization nuclei. This study investigated the effects on mineralization of variable delays between harvest of bovine pericardium and initial glutaraldehyde treatment, using tissue implanted subcutaneously in rats for 21 days. Susceptibility to mineralization increased statistically but only modestly with delays to 34 h. This suggests that mineralization will not be significantly inhibited by rapid treatment of otherwise properly handled tissue and that clinically important prevention of calcification will require more dramatic means.
The use of dense alumina–alumina ceramic combination in total hip replacement
Authors: Boutin P. , Christel P. , Dorlot J.‐M. , Meunier A. , de Roquancourt A. , Blanquaert D. , Herman S. , Sedel L. , Witvoet J. 
Published: December 2004

AbstractThe purpose of this article was to review the laboratory and clinical performances since 1970 of a total hip prosthesis using alumina–alumina combination. The chemical and physical properties of dense alumina ceramic were studied in relation to biocompatibility, mechanical strength, and surface properties. Through the examination of 35 retrieved implants, it was found that the long‐term success of alumina–alumina total hip replacement depends on both the ceramic microstructure (small grain size with uniform distribution, minimum porosity, absence of inclusions) and implant geometry (sphericity deviation ±1 μm, radius tolerance between components 7–10 μm). Alumina component wear and fractures have disappeared with the use of high‐performance materials and severe manufacturing quality control. Examination of human biopsies from well‐fixed prostheses showed that alumina particles deposits increase with time with only a low‐grade macrophagic reaction. When loosening occurred, an inflammatory reaction appeared; this reaction was less striking than with loose metal–polyethylene prostheses, however. The long‐term behavior of cementless alumina cup fixation depends upon initial positioning and stability; survivorship analysis of the cemented ceramic cups showed an 88% survival probability after 8 years with a 1.6% average annual probability of revision. The percentage of surviving was 100% after 8 years in patients who were less than 50 years old. Aseptic loosenings occurring at the cup–cement interface were assumed to be related to stress protection secondary to the high rigidity of the ceramic leading to a weakening of the spongious bone supporting the cement mantle. Good bone stock quality as well as high‐quality ceramic appear to be the prerequisites for durable fixation of alumina sockets.
A preliminary durability study of two types of low‐profile pericardial bioprosthetic valves through the use of accelerated fatigue testing and flow characterization
Authors: Schuster Paul R. , Wagner James W. 
Published: December 2004

AbstractBioprosthetic heart valves are being used more often because of certain advantages they have over artificial valves. The bioprostheses are less thrombogenic, cause a lower incidence of hemolysis, and usually fail in a slow progressive manner. A combination of flow characterization and accelerated testing was used to assess the durability of two types of pericardial valves, the Ionescu‐Shiley Low Profile Mitral and the Carpentier‐Edwards Low Profile Aortic valve. The flow characterization work was done in an aortic chamber designed for in vivo simulation. The function of the valve was monitored between different stages of the accelerated testing using laser Doppler anemometry. Accelerated testing was performed at 1300 cardiac cycles per minute, and physiologic conditions both in closing pressures and the ambient temperature were maintained. Results indicated a change in flow characteristics owing to cyclic loading of the leaflet tissue. The flow orifice increased over time leading to a decrease in peak velocity. Future developments in Doppler ultrasound may facilitate non‐invasive assessment of these peak velocity variations. Calcification of the tissue was not considered, since this was an in vitro study.
Effect of heparin–pva hydrogel on platelets in a chronic canine arterio‐venous shunt
Authors: Cholakis Cynthia H. , Zingg Walter , Sefton Michael V. 
Published: December 2004

AbstractPolyvinyl alcohol (PVA) hydrogel, with or without heparin, was reactive towards canine platelets in a chronic artriovenous shunt as demonstrated by an increase in platelet regeneration time, a systemic decrease in platelet count and transient decrease in platelet serotonin content. Immobilized heparin (heparin–PVA) had no effect whereas unmodified polyethylene was found to be unreactive despite similar levels of platelet deposition as measured by SEM and a higher in vitro reactivity (J. Biomed. Mater. Res., this is sue). Tewnty‐centimeter lengths of hydrogel coated polyethylene tubing were inserted between the arterial and venous portions of the shunt and left in place for 4–6 days, without the complicating artifacts of anticoagulation, anesthesia, or surgical intervention. Regeneration time was measured as the return to normal platelet cyclooxygenase (co) activity after a single 240‐mg dose of aspirin, with co activity measured in vitro as malondialde hyde production. Although measuring new platelet production, regeneration time is an indirect measure of platelet consumption, so that the reduced regeneration time seen here was presumed to reflect enhanced material associated consumption and thromboembolism. Like other hydrogels, PVA does not appear to be “thromboadherent” but it does appear thrombogenic. Immobilized heparin had no additional effect, presumably because the platelet response was dominated by the reactivity of the underlying substrate.
The bovine pericardial xenograft: I. Effect of fixation in aldehydes without constraint on the tensile viscoelastic properties of bovine pericardium
Authors: Lee J. Michael , Haberer Sean A. , Boughner Derek R. 
Published: December 2004

AbstractTensile testing of tissue strips has been used to examine the effect of simple fixation in glutaraldehyde and formaldehyde on the viscoelastic properties of bovine pericardium. To assess tissue anisotropy, tissue strips were cut at 0°, 30°, 60°, and 90° relative to the base‐to‐apex direction. Fresh anterior pericardium was modestly anisotropic, being least extensible in the base‐to‐apex direction; however, fixation removed this anisotropy. Fixation also produced a marked change in the response of the material to initial cyclic loading during preconditioning. Overall extensibility of the fixed material was significantly greater than that for the fresh tissue, consistent with a 10.7% shrinkage in aldehydes calculated from strain at fracture data. Reductions in stress relaxation and creep after fixation were noted as well, consistent with intrafibrillar crosslinking. Cyclic hysteresis and ultimate tensile strength were unaffected. Since the observed changes in the stress–strain response were largely attributable to shrinkage, control of shrinkage by physical means would allow for engineering modification of bovine pericardial mechanics for controlled anisotropy.
Fracture behavior of urinary stones under compression
Authors: Ebrahimi F. , Wang F. 
Published: December 2004

AbstractThe fracture behavior of two types of urinary stones, namely struvite and calcium oxalate, during compression testing was studied. Scanning electron microscopy (SEM) was used to characterize the fracture surfaces. Both types of stone showed pseudo‐plastic behavior as indicated by their load‐displacement curve. The onset of nonlinear behavior was found to correspond to development of microcracks in the specimens. The compressive strength was defined as the stress calculated at the maximum load. In struvite samples, the maximum load corresponded with the development of large cracks parallel to the compressive axis. For oxalate stones a separation of the outer layer (crust) from the inner layer (core) marked the point of maximum load. The compressive strength of the struvite samples was found to depend on the orientation of lamellae relative to the loading axis. Struvite stones, when loaded parallel to the lamination direction showed a higher compressive strength than oxalate stones did. The fracture behavior and compressive strength of a model material (z‐brick) were also characterized and compared to those of the urinary stones.
Biomechanical considerations on some postoperative problems of directly anchored total hip replacements
Authors: Heimke G. , Stock D. , Büsing C. M. , Mallinckrodt D. V. 
Published: December 2004

AbstractUncemented total hip replacements have resulted in a higher incidence of postoperative complaints than cemented ones. The theoretical explanation of these not well defined discomforts is based on the differences of the stress and strain fields around the distal portions of the femoral components. While the noncemented stems are press‐fitted and most of them tapered distally, thus creating hoop stresses and strains in the surrounding cortical bone, the shrinkage of the cement prevents these mechanical irritations. The relatively sudden disappearance of these discomforts within the first 2 postoperative years is attributed to the shift of the main zone of load transmission from the distal to the proximal portion of the stems following bone remodeling.
Generation of IL1‐like activity in response to biomedical polymer implants: A comparison of in vitro and in vivo models
Authors: Miller Kathleen M. , Rose‐Caprara Veronica , Anderson James M. 
Published: December 2004

AbstractOf the many factors determining host biocompatibility responses to implanted biomedical polymers, the cellular interactions at the tissue/material interface have been recognized to be some of the most important. The present study has combined results both from an in vitro cell culture system and from an in vivo animal model to examine this host response. In vitro results suggest that a variety of polymer materials can differentially activate human monocytes to produce a protein(s) having different biological activites. The polymers tested induce the production of the regulatory inflammatory protein interleukin 1 as well as a factor that enhances fibroblast proliferation and collagen synthesis. The observed activities of these factors appear to be related but not identical, and are dependent upon the specific polymer. Evaluation of exudate and tissue responses to these same polymer materials in an in vivo model are also presented. Both in vitro and in vivo results support the hypothesis that monocyte/macrophage activation with subsequent synthesis of regulatory factors such as interleukin 1 plays a significant role in determining the host response to biomedical polymer implants.
The influence of calcium phosphate ceramics and glass‐ceramics on cultured cells and their surrounding media
Authors: Hyakuna Katsufumi , Yamamuro Takao , Kotoura Yoshihiko , Kakutani Yoshiaki , Kitsugi Toshiaki , Takagi Haruki , Oka Masanori , Kokubo Tadashi 
Published: December 2004

AbstractThe cytotoxicity of hydroxyapatite (HA), tricalcium phosphate (TCP), and two types of phosphate (TCP), and two types of apatite‐containing glass‐ceramics designated A · W‐GC and A · W · CP‐GC was evaluated by the direct contact method using V79 cells. Compatibility of the cells was assessed as a function of cellular attachment and subsequent growth using scanning electron microscopy. Although all of the tested materials have surfaces available for cellular attachment, cell growth was markedly inhibited by HA sintered at 600°C and 900°C, and slightly inhibited by HA sintered at 1200°C, TCP and the glass‐ceramics. In attempts to clarify the cause of this toxicity, the interactions of the ceramics with culture medium was assessed by measurement of calcium (Ca), inorganic phosphate (P), magnesium (Mg), pH and albumin content in the medium. The grade of toxicity corresponded to the degree of reduction of Ca, P, and albumin in the medium. Furthermore, surface reactions of the ceramics were demonstrated to vary in both mode and degree depending on their chemical structure and level of microporosity. Thus, the surface reactivity of ceramic materials should be always taken into account in discussing their biocompatibility in vivo.