摘要:

AbstractEfforts to explain blood compatibility with synthetic and natural surfaces based on a single parameter or a single biological test procedure have either been unsuccessful or led to misleading generalizations. The problem reflects the complex interdependence between material's properties, the composition and properties of blood, andin vivobiorheological conditions. Among the initial events that occur when materials contact blood is the very rapid adsorption of plasma proteins; this process effectively influences the subsequent interactions with the formed blood elements, especially the platelets with the proteinated surfaces.In the case of natural surfaces, when the endothelium is damaged, collagen may become exposed that may cause the activation, adhesion, and aggregation of platelets leading to thrombosis. Current evidence indicates that the platelet‐aggregating ability of collagen depends on its “multimeric” or fibrillar structure, rather than on the activation of the platelet‐bound enzyme system. Under normal conditions, the flowing blood is probably not in direct contact with endothelial cells that line the blood vessel walls, but with an adsorbed layer of plasma proteins. Should a formation of a multilayer of plasma proteins occur following the initial adsorption of a monolayer, this process could be influenced by changes in the solubility of the proteins, especially fibrinogen, the solubility of which is quite low in plasma. The hypothesis is proposed that such changes may be intimately related to the electrical properties of proteins present in the vascular wall and in blood. It is possible that these properties play a much greater role in thrombogenesis and in the problem of blood compatibility than is currently appreciated.Considering synthetic polymers, a number of these have been prepared that exhibit little adverse effects on blood components and, at the same time, retain their physical properties for various periods of time in the physiological environment. These combined biological and physical properties make them useful for various prosthetic and other biomedical applications in surgery and

ISSN:0021-9304    

DOI:10.1002/jbm.820110103

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThrombus formation on a foreign surface is a complicated process, involving many factors. However, there is little doubt that a foreign surface adsorbs plasma proteins upon blood contact and that the nature of this adsorbed layer may determine the mechanism of platelet adhesion and aggregation. The adhesion and aggregation of platelets play an important role in the initial events of thrombus formation on a foreign surface. In this work, adsorption studies using human blood plasma were done on several polymer surfaces. Some drugs which prevent platelet adhesion were utilized to verify the proposed mechanism for platelet adhesion which includes glycosyl transferase reaction. Also, adsorption and release of fatty acid salts, including fatty acid‐bonded albumin, were investigated at different polymer interfaces. It is postulated that adsorbed fatty acid salts are released from the surface upon contact with plasma to form a high local concentration of fatty acid, and that this fatty acid suspension would cause platelet aggregation at the interfac

ISSN:0021-9304    

DOI:10.1002/jbm.820110104

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractFactors which contribute to measurement errors associated with the use of radiotracers to measure protein adsorption are considered. Techniques for removal of excess adsorbent solution and for estimation of surface area are described. Artifacts induced by the incorporation of a radio‐label both by specific adsorption of the labeling atom and by changes in the protein are discusse

ISSN:0021-9304    

DOI:10.1002/jbm.820110105

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractWe have studied the contact interaction of platelets with hydrogels. In the form of microspheres, 0.6–1.0 μ, poly (glycol methacrylate) (poly HEMA) and poly (methyl methacrylate) beads cause platelets to aggregate at concentrations of about 108beads/ml. Polyacrylamide and (20/80) poly (acrylamide–HEMA) copolymer were ineffective in aggregating platelets. The admixture of 20% methacrylate to polyHEMA rendered the beads inactive. Blood plasma components other than fibrinogen were found essential to the interaction of the beads with platelets. Near‐infrared spectra of the hydrogels polyacrylamide and polyHEMA showed the water hydrogen bonds to be the same for both and different from those in pure water. The monomer HEMA is an inhibitor of platelet aggregation and the release reaction at levels of 0.1%. It is concluded that the two hydrogels have different blood compatibilities, which depend more on the network structures than the water structures in the respectiv

ISSN:0021-9304    

DOI:10.1002/jbm.820110106

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractTo quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent‐cast films of two analogous poly (ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposedex vivoto canine blood under the well‐defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their “Composite Surface Free Energy Function,” γ′s, which describes the surface force field as the sum of the mean dispersion (\documentclass{article}\pagestyle{empty}\begin{document}$ \bar \gamma $\end{document}sd) and polar (\documentclass{article}\pagestyle{empty}\begin{document}$ \bar \gamma $\end{document}sp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear‐limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface‐number density of platelets, [Ps], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC‐circle diameter and [Ps] scale with\documentclass{article}\pagestyle{empty}\begin{document}$ \bar \gamma $\end{document}sp/γ′s, implying that (1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, (2) the primary determinant of surface‐induced effects is the polar force contribution, and (3) the magnitude of γ′sis secondary if\documentclass{article}\pagestyle{empty}\begin{document}$ \bar \gamma $\end{document}sd/

ISSN:0021-9304    

DOI:10.1002/jbm.820110107

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe Avcothane 51 elastomer, a member of a series of proprietary materials best characterized as polyurethane/poly(dialkylsiloxane) block copolymers, displays considerable hemocompatibility without any incorporated anticoagulants. In the form of intra‐aortic balloons, the elastomer was implanted in several thousands of cardiac patients without intolerable hematologic effects. Hemocompatibility has been assumed to result from a predominantly dispersion‐type surface force field whose intensity fluctuates within small domains, maintaining adsorbed blood proteins in an unstable state. The relative hemocompatibility of films, which were obtained from a prepolymer solution cast on substrates impenetrable to the solvent, is a function of the effective surface molecular structure. This can vary as a function of preparative conditions (temperature and rate of evaporation), and has been correlated with an anisotropic distribution of the silicone component in cured films. The concentration of this component in surface layers was quantified independently by IRATR spectroscopy and electronmicroprobe analysis, giving consistent results. An IRATR index, which is computed from the ratio of absorptivities measured at 13.00 and 12.62 μ and is inversely proportional to the relative silicone content of surface layers, was found to correlate with the apparent hemocompatibility determined by differentin vitromethods. Optimized reproducible hemocompatibility is attained by strict process cont

ISSN:0021-9304    

DOI:10.1002/jbm.820110108

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe pseudoneointima (PNI) deposited onto a cardiac prosthesis surface reflects many factors of biocompatibility, surface morphology, flow distribution, design, animal's physiological condition, and duration. In the evaluation of any prosthesis, the PNI is one of the prime considerations from both material and functional standpoints.Historically, Dacron fabric has been used as an internal lining for cardiac prostheses. However, we have observed cracks on the Dacron fibers, fiber fracture, fiber protrusion, and poor attachment to the diaphragm, which can cause potentially disastrous complications. In addition, there are basic differences in the PNI formation on aldehyde‐treated pericardium and natural aortic valves as compared to the Dacron fabric.1Minimal degeneration takes place on the chemically treated natural tissue compared with the fabric surface. Intact cells on the tissue suggest a greater compatibility. In later specimens (13 and 24 days), there is active cell infiltration into the pericardium structure with capillary formation.2The deposits on natural tissue are mostly fibrin, with minimum cellular involvement and a trend toward reduction in thickness.3Fibroblast cells are found on the natural tissue as early as 7 days but were not observed on the Dacron fabrics.Based on these findings, the Dacron fabric‐covered diaphragm studied was not favorable for use in long‐term implantation of cardiac prost

ISSN:0021-9304    

DOI:10.1002/jbm.820110109

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractPolyionenes have been shown recently (A. Rembaum,Appl. Polym. Symp. No. 22, 299, 1973) to produce the following biological effects: (1) bactericidal action, (2) formation of insoluble complexes with DNA and heparin, (3) neuromuscular blocking action, (4) cell aggregation and lysis, and (5) cell adhesion.In the present study, polyionenes of various structures (mainly I3,3, I6,10) were used as molecular probes to gain an understanding of the cell surface phenomena of adhesion on glass‐ and polyionenes‐treated surfaces. Since tumor cells show different surface cell properties, including an increase in the anodic mobility, they bind preferentially to polyionene‐treated surfaces. Normal human diploid WI‐38 cells were found to adhere at a lower rate than SV‐transformed WI‐38 cells. However, cell spreading was accelerated in both cases.A study of the interaction of polyionenes in solutionin vitroandin vivoand polyionenes covalently bound to polymeric microspheres with leukemic murine EL 4 cells and normal thymocytes showed specific cytotoxity towards the leu

ISSN:0021-9304    

DOI:10.1002/jbm.820110110

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe enzymatic activity of α‐chymotrypsin (CT), immobilized on hydrogelcoated polymer film supports, has been investigated. The support was prepared by radiation‐graft copolymerization of 2‐hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAAc) on silicone rubber films. The enzyme was covalently coupled to the carboxylic group of MAAc via theN‐hydroxysuccinimide (NHS) ester active intermediate.Increasing MAAc contents of the hydrogel resulted in increased attachment of CT. The integrity of the CT active site after attachment was assessed by an active site titration with diisopropyl fluorophosphate (DFP). As the MAAc content of the hydrogel was increased, an increasing fraction of the attached CT retained its activity to DFP. A greater fraction of CT was active towards DFP when adsorbed than when coupled.The rates of hydrolysis of some synthetic model substrates by the immobilized CT were also measured. The negative charge on the hydrogel had a large effect on the rates of these hydrolyses. The pH optimum for the hydrolysis ofN‐acetyl‐L‐tyrosine ethyl ester (ATEE) by immobilized CT was higher than that of free CT. Increasing MAAc content of the hydrogel resulted in larger shifts in the pH optimum. The maximum rates of ATEE hydroylsis per mg CT declined sharply with increasing MAAc content of the hydrogel. This is probably related to the increasing repulsive force between the ATEE (negatively charged above ⋍ pH 9.5) and the hydrogel with increasing MAAc content. The activity of immobilized CT to ATEE is small compared to that of free CT, partly due to this charge effect. Conversely, the rate of hydrolysis of BAEE, a positively charged substrate, by immobilized CT at pH 11, is almost fourfold greater than that by free CT a

ISSN:0021-9304    

DOI:10.1002/jbm.820110111

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper is concerned with the evaluation of thein vivoperformance characteristics of reconstituted bovine collagen as an insoluble carrier matrix for therapeutic enzymes. The enzyme that was chosen as a model for this evaluation wasE. coliL‐asparaginase, which has been widely investigated as a soluble chemotherapeutic agent for the treatment of acute lymphocytic leukemia in humans (Oettgen et al.,Cancer Res.,27, 2619, 1967; Beard et al.,Brit. Med. J.,1, 191, 1970; Ohnuma et al.,Cancer Res.,30, 2297, 1970). The results presented here were obtained from perfusion trials with a collagen–asparaginase reactor incorporated into an extracorporeal circuit attached to the vascular systems of healthy mongrel dogs. A series of 1–2 hr perfusions were conducted with a single collagen‐asparaginase membrane over a period of 4 months. Serum asparagine levels were reduced by more than 98% after 15–30 min perfusion time. Red blood cell (RBC), hemoglobin, hematocrit, and fibrinogen values remained constant during each perfusion. An average decrease of 48% in white blood cell (WBC) and 24% in platelet levels was observed, but these values began to rise slowly even before cessation of the perfusion. No serious toxic or antigenic reactions or mechanical or clotting difficulties were observed.In vitroactivity, when assayed between perfusions, remained constant over a period of 4 months of intermittent use and storage. The potential advantages of collagen–enzyme complexes for the administration of therapeutic enzymes i

ISSN:0021-9304    

DOI:10.1002/jbm.820110112

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY