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Results for “Polyurethanes”

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At least 451 records · Page 25Linked to original sources

PubMed1993

Comparative study of the function of the Abiomed polyurethane heart valve for use in left ventricular assist devices.

Hydrodynamic testing of the Abiomed polyurethane trileaflet valve has been carried out to establish performance data of valve function. A Medtronic Hall tilting disk, a Carbomedics bileaflet, a Hancock II bioprosthesis and an Abiomed polyurethane trileaflet valve, all size 27 mm, underwent both pulsatile and steady-flow hydrodynamic testing. Results of the variation of pressure difference with RMS pulsatile flow and steady flow, and effective orifice area, showed that the Abiomed valve had significantly poorer opening characteristics than the tissue valve and the two mechanical valves. The Abiomed valve's performance was seen to be related to its construction and manufacture. This study highlights some of the problems associated with the design and development of synthetic trileaflet heart valve prostheses.

Biocompatible Materials↗

PubMed1982

Polyether polyurethanes for implantable pacemaker leads.

Two variations of a commercially available polyether polyurethane were evaluated for certain physical properties and the changes in those properties as a result of plasticization by absorbed moisture. Appropriate tests were done to establish biocompatibility. A two-year rat implant study evaluated chronic biocompatibility and biostability. Ten tumours were found in 34 animals, of which eight were considered unrelated to the materials. Two fibrosarcomas were presumed to be the result of solid-state carcinogenesis, not related to the material per se. Material testing included analysis of density, tensile strength, elongation, molecular weight, intrinsic viscosity, scanning electron microscopy, differential scanning calorimetry, and infrared spectrum changes. The polyether polyurethane was considered to be biocompatible and biostable for long-term implant.

Animals↗

PubMed1985

Effects of implantation on the mechanical properties of the polyurethane diaphragm of left ventricular assist devices.

Tensile properties of blood pump diaphragms made from a segmented polyether polyurethane (Toyobo TM5) were studied after implanting in goats for variable periods of time up to 72 days. The implantation decreased the tensile strength and ultimate elongation at break, while the elastic modulus increased very slightly. These changes in the strength and ductility were primarily caused by the contact of material with blood rather than by the mechanical fatigue of material. Mechanical stability was greatly improved by removing residual oligomers from the material by a refining procedure. The refined polyurethane has characteristics favourable for blood pump applications.

Animals↗

PubMed1986

Coating of two polyether-polyurethanes and polyethylene with a heparin-poly-(vinyl alcohol) hydrogel.

Two polyether-polyurethane elastomers (Pellethane and Biomer) and polyethylene were coated with a heparin-poly(vinyl alcohol) hydrogel. The requisite surface modification in preparation for coating consisted of glow discharge cleaning and acid treatment for the polyether-polyurethanes and glow discharge cleaning and chromic acid oxidation for polyethylene. The chemical modifications increased surface wettability. Surface analysis by attenuated total reflectance Fourier transform infrared spectroscopy indicated that the acid treatment caused hydrolysis of the polyether segments of Pellethane and Biomer. Prolonged partial thromboplastin times were observed on the coated films. The results of toluidine blue assay of heparin in the solution in which the coated films were immersed for a long time suggested that heparin was covalently bound in the coating. Such coating techniques extend the usefulness of the heparin-poly(vinyl alcohol) hydrogel to a number of medically important substrate materials.

Biocompatible Materials↗

PubMed1987

Properties of extruded poly(tetramethylene oxide)-polyurethane block copolymers for blood-contacting applications.

The bulk and surface properties and blood compatibility of a series of polyurethanes based on methylene bis(p-phenyl isocyanate), 1,4-butanediol, and poly(tetramethylene oxide) of molecular weight 1000 were studied. The hard-to-soft segment ratio of these multiphase polymers was varied, and the effect of substituting a poly(dimethylsiloxane)-containing polyol in place of 5% of the polyether soft segment was studied. Bulk properties such as tensile strength and modulus increased with hard segment content, as did surface wettability and ESCA nitrogen content. However, blood compatibility measured by a canine ex vivo blood-contacting experiment was not found to vary with hard/soft segment ratio. The addition of the silicone-containing polyol did not significantly lower the surface wettability, although ESCA-measured silicon content increased and physical properties were unfavourably affected by the incorporation of this co-soft segment. Incorporation of the siloxane-containing component resulted in increased platelet adhesion and fibrinogen deposition at most blood contact times in comparison with the other polyurethanes.

Animals↗

PubMed1987

Chemical and biological evaluation of heparinized poly(amido-amine) grafted polyurethane.

By a simple process poly(amido-amine) chains have been grafted onto the surface of polyurethane. The poly(amido-amine) was found to be able to complex heparin by electrostatic interaction. Heparin can be released only at pH greater than 10 with NaOH solution. The heparin adsorbing capacity of the material was biologically tested, and the anticoagulant activity of the heparinized polyurethane was demonstrated.

Adsorption↗

PubMed1988

Extraction of polyurethane block copolymers: effects on bulk and surface properties and biocompatibility.

In order to study changes occurring in polyurethane block copolymers upon solvent extraction, a base polymer containing approximately 50% polyurethane hard segment based on 4,4'-bis(p-phenyl isocyanate), 1,4-butanediol, and poly(tetramethylene oxide) of MW 1000 was synthesized. Portions of this polymer were extracted using methanol, toluene, and acetone. Multidetector gel permeation chromatography was used to characterize the effect of extraction on molecular weight and molecular weight distribution. Extraction also affected bulk and surface properties and the blood compatibility as assessed using a canine ex vivo blood-contacting experiment. Extracted materials possessed a higher molecular weight than the base polymer and had narrower molecular weight distributions. Acetone extraction resulted in the polymer with the highest ultimate tensile strength. Contrary to expectations, the surface properties and blood compatibility of the material studied were affected minimally by extraction.

Biocompatible Materials↗

PubMed1988

Albumin adsorption on alkyl chain derivatized polyurethanes. II. The effect of alkyl chain length.

Linear alkyl chains containing 2, 10 and 18 carbon atoms were grafted to 10% of the urethane nitrogens in a polyether-polyurethane. The polyurethane was synthesized from methylene bis(p-phenyl isocyanate), 1,4-butanediol, and polytetramethylene oxide of 1000 molecular weight in a molar ratio of 3/2/1. Fourier transform infrared spectroscopy and attenuated total reflectance optics were used to study the adsorption of 5.0 mg/ml human serum albumin (HSA) at 37 degrees C to the derivatized and non-derivatized polymers. Both delipidized HSA and HSA containing 6.5 mol stearic acid per mol of albumin were used to study the effect of chain length upon the initial adsorption rate, the total amount adsorbed in 1 h, and the desorption rate. The initial adsorption rates revealed that non-specific adsorption was similar upon all four polymers. An increase in initial adsorption rate upon the C-18 derivatized polymer was attributed to a specific binding interaction between the HSA and the grafted alkyl chains. The conformational stability of the HSA also affected the adsorption rate. The total amount adsorbed after 1 h decreased as the alkyl chain length increased from 2 to 18 methylene groups. The desorption rate decreased in magnitude as the alkyl chain length increased from C-2 to C-18. These results support a hypothesis that alkyl chain length influences the interaction between albumin and an alkylated polymer system.

Adsorption↗

PubMed1989

Bulk, surface and blood-contacting properties of polyether polyurethanes modified with polydimethylsiloxane macroglycols.

The bulk, surface and blood-contacting properties of a series of polyether polyurethanes, modified with three different polydimethylsiloxane (PDMS) macroglycol segments, were evaluated. The PDMS oligomers were terminated with hydroxy-tipped end groups of varying polarity. The effect of substituting the polytetramethylene oxide (PTMO) soft segment of a base polyurethane with 5 and 15 wt% of these PDMS-containing polyols was investigated. The ultimate tensile strength and elongation at break appeared to be the bulk properties most significantly affected by the addition of the PDMS-containing polyols. Underwater contact angle data indicate that the block copolymer surface became more hydrophilic with increasing PDMS content. In a vacuum, as determined from the ESCA data, the relatively non-polar PDMS soft segments preferentially oriented at the surface with increasing PDMS incorporation. Despite the variation in the surface properties, the blood compatibility of these polymers was not significantly affected by the addition of the PDMS-containing polyols.

Animals↗

PubMed1991

Development of a new in vitro model for studying implantable polyurethane calcification.

The objective of this study was to reproduce mineralization of polymeric substrate in an extracirculatory environment which would facilitate investigation of the calcification mechanism in implantable biomaterials and methods of prevention. Calcification was examined on polyurethane films incubated in metastable solutions of calcium phosphate and the role of strain, serum and polymer porosity was examined. Validation of the model was evaluated by examining the calcification of both highly calcifiable biomaterial (bioprosthetic tissue) and a non-calcifiable biomaterial (charge-modified tissue and polyurethane containing anticalcification agent). It is concluded that the developed model is adequately sensitive to diagnose biomaterials' propensity to calcify and could serve as a pre-screening method to examine calcification mechanism and methods of prevention.

Biocompatible Materials↗

PubMed1992

Anticoagulant effects of sulphonated polyurethanes.

Sulphonated polyurethanes have been shown to have excellent blood contacting properties. In this paper, similar polyurethanes which are water soluble have been investigated to determine their influence on thrombus formation. These polymers were shown to delay clotting times in the following ways: by direct complex formation between the polymer and thrombin; by interference with fibrin polymerization; and by complex interactions between polymer, thrombin, plasma antiproteases and fibrinogen in plasma.

Animals↗

PubMed1992

Design of a polyurethane membrane for the encapsulation of islets of Langerhans.

A semipermeable membrane for the encapsulation of the islets of Langerhans, consisting of a microporous polymer network, has been developed. The polyurethane network was formed by cross-linking a mixture of linoleic acid and a linear poly(etherurethane) with dicumyl peroxide. Cross-linking the polyurethane impedes the formation of hard domains. Miocroporosity was introduced by adding salt crystals of different sizes before cross-linking and leaching it out afterwards. To optimize the permeability and immunoprotectivity, membranes were prepared with three different porosities. Membranes of this material were filled with islets of Langerhans and implanted in the peritoneal cavity of rats. Short-term in vivo experiments in rats show that membranes with pores in the range 0.3-0.7 micron and a wall thickness of about 8 microns were permeable for insulin and glucose and protected the islets of Langerhans against the cells of the immunological system.

Animals↗

PubMed1992

In vitro leucocyte adhesion to modified polyurethane surfaces. I. Effect of ionizable functional groups.

To study the effect of ionizable functional groups on the adhesion of leucocytes to surfaces, both poly(ethyleneimine) and poly(acrylic acid) were immobilized on polyurethane films, resulting in the introduction of amine and carboxylic acid groups, respectively. This was confirmed by contact angle measurements and XPS analysis. In vitro adhesion of granulocytes and lymphocytes on untreated and modified surfaces was compared. The number of adherent cells on modified surfaces as a function of time was significantly higher than on untreated surfaces. This effect was most pronounced for the adhesion of lymphocytes to surfaces modified with amine groups. In this case, the number of adherent cells after 1 h of exposure was three times higher than on untreated surfaces. A moderate enhancement of leucocyte adhesion was observed in the case of surfaces modified with carboxylic acid groups. There is evidence that these groups were not ionized under the experimental conditions used. The modification procedures described may be used to improve polyurethane filters for the removal of leucocytes from blood.

Cell Adhesion↗

PubMed1992

Seeding of enzymatically derived and subcultivated canine endothelial cells on fibrous polyurethane vascular prostheses.

Fibrous polyurethane (FPU) prostheses with or without fibronectin coating and gelatin impregnation and FPU prostheses with or without fibronectin coating were seeded with 4.8 x 10(5) subcultivated dog endothelial cells per cm2 prosthesis. Expanded polytetrafluoroethylene (ePTFE) prostheses with and without fibronectin coating served as controls. The numbers of cells retained on uncoated polyurethane prostheses were minimal but increased with fibronectin coating and/or gelatin impregnation. Adhering cells were predominantly round in shape and few cells were seen stretched over the prosthetic fibres. Optimum numbers of cells were found in prostheses impregnated with gelatin and coated with fibronectin, where almost all the cells were stretched forming a confluent monolayer. In ePTFE prostheses only minimal numbers of cells were retained but in the fibronectin-coated prostheses a high cell count was noted. Gelatin-impregnated and fibronectin-coated FPU prostheses, as well as ePTFE prostheses coated with fibronectin, were additionally perfused in vitro after seeding under nearly physiological conditions for 1 h. Cells in the FPU prostheses were still present after perfusion, whereas all the cells in the ePTFE prostheses were lost from the inner surface. It is concluded that FPU prostheses impregnated with gelatin and coated with fibronectin are a suitable substrate for subcultivated endothelial cells to be seeded on. The cells remained at the surface even after 1 h in vitro perfusion with tissue culture medium under nearly physiological conditions. Further research including in vivo implantations is indicated.

Animals↗

PubMed1994

Biocompatibility of silver-coated polyurethane catheters and silver-coated Dacron material.

The local effects of silver-coated polyurethane catheters and Dacron material were compared to uncoated polyurethane catheters and Dacron material in a long-term implantation test using rabbits. The tissue-implant interaction was analysed by investigating the type and number of inflammatory cells, capillaries, fat tissue, the extent of fibrosis, thickness of the fibrous capsule, number and distribution of silver particles, and the size of giant cells. Silver-coated and uncoated materials displayed comparable signs of inflammation and tissue reaction.

Animals↗

PubMed1994

Hydrolytic stability of polyurethane medical adhesive dressings.

The present study deals with the effect of the type and chemical character of incorporated polyester (polyether blocks) on the hydrolytic stability of different types of polyurethane medical adhesive dressings. Diffusion parameters of the investigated polyurethane adhesives, giving information concerning the chemical changes taking place in water or physiological solution, have also been determined.

Adhesives↗

PubMed1995

Calcification and fatigue failure in a polyurethane heart value.

The prosthetic heart valves were fabricated from a polyurethane containing a 4,4'-diphenylmethane diisocyanate hard segment, chain-extended with butanediol and with a polyether soft segment. The rate of calcification of these polyurethane heart valves was much slower in a dynamic in vitro test system than similar bioprosthetic heart valves. The calcified deposits were located exclusively at regions of material failure. Fourier transform infrared (FTIR) spectroscopy indicated the involvement of the polyether soft segments of the polymer directly in the calcification process. Calcification of polymer fractions also suggested that small molecular weight extractable components are accelerating factors in the calcification process.

Animals↗

PubMed1996

Tissue response to commercial silicone and polyurethane elastomers after different sterilization procedures.

Two different commercial polymeric materials, a silicone and a polyurethane (PUR), were studied with regard to correlations between the chemical and physical compositions of the polymer surfaces and the biological response on implantation. Test specimens of the materials were manufactured according to standard procedures. The specimens were implanted in rats for 10 and 90 days. Before implantation the polymers were sterilized in three different ways, namely, beta irradiation, ethylene oxide sterilization and steam sterilization. The polymers were characterized before and after the implantation with respect to the chemical composition and the morphology of the surfaces. After implantation the biological response was evaluated by counting numbers of macrophages, giant cells, fibroblasts and other cells present at the surfaces. The thickness of the fibrous capsule surrounding the test specimens was measured at the thickest and thinnest parts. PUR surfaces showed signs of degradation already after sterilization and after 10 to 90 days of implantation, pits and cracks appeared, especially in the ethylene oxide sterilized samples. However, differences in the biological responses were small and independent of the sterilization method. After 10 days of implantation the capsule thickness and the amounts of cell material adhering at the surfaces were different, and it appears that the silicone rubber induces more tissue response than PUR. The differences in the early tissue response evened out after 90 days implantation time and a steady state situation evolved, which was similar for the silicone and the polyurethane.

Animals↗