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At least 127 records · Page 7Linked to original sources

PubMed1998

Surface modification of polyurethane heart valves: effects on fatigue life and calcification.

Polyurethane heart valves can be functionally durable with minimal calcification, in vitro. In vivo, these characteristics will depend on the resistance of the polyurethane to thrombogenesis and biodegradation. Surface modification may improve the polyurethane in these respects, but may adversely affect calcification and durability. This study investigates the effects of surface modifications of two polyurethane heart valves (PEU and PEUE) on their in vitro fatigue and calcification behaviour. Modifications included heparin, taurine, 3-aminopropyltriethoxysilane and polyethylene oxide (PEO). Neither hydrodynamic function nor leaflet thickness distribution was significantly altered by surface modification. PEO-modification was detrimental to valve fatigue durability and calcification. Heparin, taurine or aminosilane modifications of PEU valves increased durability. Aminosilane modification of PEUE valves increased durability compared with PEO modification. Appropriate surface modification may be useful to improve blood compatibility of implantable polyurethanes, and may also be advantageous as regards fatigue durability of flexing materials in longterm applications.

Analysis of Variance↗

PubMed1998

Biocompatibility of polyurethane-coated stents: tissue and vascular aspects.

To assess the arterial injury triggered by polyurethane-coated vs. uncoated stents, six polyurethane-coated and six bare nitinol stents were implanted in rabbit carotid arteries. All animals were sacrificed 4 wk after stent placement. Sections were evaluated by histology and morphometric analysis. At 4 wk, both the coated and uncoated stent struts were entirely endothelialized. The spaces between the struts showed a relatively mild proliferative response, with a few sections demonstrating neovascularization around the struts. Polyurethane coating was associated with an inflammatory tissue response consisting of lymphocytic infiltration and foreign-body reaction, with the appearance of multinucleated giant cells. Lumen, intimal, and medial cross-sectional areas varied little between coated and uncoated stented vessels (2.45+/-0.19 vs. 2.47+/-0.47 mm2, 1.17+/-0.52 vs. 0.78+/-0.30 mm2, and 0.66+/-0.18 vs. 0.58+/-0.27 mm2, respectively). In the rabbit carotid artery model, polyurethane coating does not affect the degree of neointimal proliferation after endovascular stenting compared with the conventional stenting approach. However, the inflammatory tissue response may indicate a low intrinsic biocompatibility of this stable polymer, so that it may not be an ideal material for coating intravascular devices.

Animals↗

PubMed1999

Assessing the resistance to calcification of polyurethane membranes used in the manufacture of ventricles for a totally implantable artificial heart.

Ventricles made from segmented polyurethane membranes and used in the fabrication of a totally implantable artificial heart are known to undergo biomaterial-associated calcification. As there is no effective method currently available to prevent such biomaterials from calcifying, a practical solution is to use only materials with a relatively high resistance to calcification, to extend ventricular durability and ensure a longer functional life for the manufactured device. In the present study, an in vitro calcification protocol was used to determine the relative resistance to calcification of six different polyurethanes, namely, Carbothane PC3570A, Chronoflex AR, Corethane 80A, Corethane 55D, Tecoflex EG80A, and Tecothane TT1074A. The results demonstrated that all six polyurethanes did become calcified during the 60-day incubation period in the calcification solution. The degree of calcification was found to be associated with the surface chemistry of the particular polyurethane, with the Tecothane TT1074A exhibiting the highest level. The Corethane 80A and 55D polymers showed a relatively low propensity to calcify. These two membranes can, therefore, be considered as the most appropriate materials for the fabrication of ventricles for a totally implantable artificial heart. In addition, since the calcification occurred primarily at the surface of the membranes, without affecting the bulk microphase structure, the issue of modifying the surface chemistry to reduce the incidence of calcification is discussed.

Biocompatible Materials↗

PubMed1999

Photobinding of [gamma-(32)P] ATP gamma-benzophenone to the surface of a polyurethane membrane in the preparation of a beta-particle-emitting balloon catheter.

PURPOSE: The goal of this study was to photochemically bind 5'-[gamma-(32)P]-azido-ATP gamma-benzophenone ((32)P-ATP-BPA) to a polyurethane surface. Expandable balloon catheters composed of (32)P-coated polyurethane have the potential for preventing restenosis following percutaneous transluminal coronary angioplasty. METHODS: After extensive preparation and cleaning of polyurethane disks, 10 microL of the radioactive ATP-BPA reagent (specific activity = 9.4 Ci/mmol) was applied to the surface. After drying, the membrane disks were exposed ultraviolet radiation (254 nm; 6,000 microwatts/cm(2)) for up to 2 h and subsequently washed. The amount of (32)P bound to the membrane disks was determined by Cerenkov counting in a liquid scintillation counter. The effect of the labeling solution composition (solvent, presence of potassium or manganese ions, addition of surfactants, etc.) on photobinding efficiency was determined. RESULTS: The efficiency of attaching the (32)P-ATP-BPA reagent to the polyurethane surfaces was markedly dependent upon the cleaning and pretreatment conditions. Following detailed washing and rinsing steps, a photobinding efficiency of 36.4+/-3.6% was obtained with 10 min UV exposure time using (32)P-ATP-BPA solutions that were 95/5 methanol/water by vol. Increasing the concentration of the (32)P-ATP-BPA reagent did not improve the photobinding efficiency; however, the total amount of (32)P bound to the disks was increased. CONCLUSIONS: Photochemical methods can be employed to attach beta(-)-emitting radionuclides to polymers that are employed as balloon catheters. The preparation of the polymeric material (washing, rinsing, and drying) is critically important in maximizing the amount of (32)P-ATP-BPA that can be bound to the polymer.

Adenosine Triphosphate↗

PubMed1991

Thrombocytopenia associated with environmental exposure to polyurethane.

Few chemicals in the environment have been implicated as causes of isolated thrombocytopenia, and the evidence is usually less than convincing because the patients were not rechallenged with the chemical in vivo. In the present paper, a child is reported with the onset of thrombocytopenia in temporal association with environmental exposure to polyurethane. Five years after the initial thrombocytopenia had resolved, an inadvertent in vivo rechallenge with environmental polyurethane resulted in recurrence of the thrombocytopenia. This recurrence, together with the fact that only 1-4% of cases of idiopathic thrombocytopenic purpura in children recur, provided strong evidence for a causal role for the polyurethane exposure in this patient's thrombocytopenia. In summary, environmental exposure to polyurethane should be considered in the differential diagnosis of acquired thrombocytopenia in childhood.

Child, Preschool↗

PubMed1994

Endothelial seeding of compliant polyurethane vascular graft material.

Compliance was measured in a new compliant polyurethane vascular graft material and in polytetrafluoroethylene (PTFE) graft material using an ultrasonic device; attachment of indium-111 oxine-labelled human endothelial cells to both surfaces with a range of surface coatings was assessed. Compliant polyurethane was six to eight times more compliant than PTFE (P < 0.01) at all pressures in the range 50-120 mmHg, and endothelial cell attachment to uncoated polyurethane was three times better than to uncoated PTFE at times up to 90 min (P < 0.01). Attachment to polyurethane was also better after blood clot, collagen and fibronectin treatment at times up to 30 min (P < 0.05). Endothelial seeding of compliant graft material may provide a prosthetic vascular substitute with characteristics similar to those of autologous vein.

Aged↗

PubMed1990

Small-caliber polyurethane and polytetrafluoroethylene grafts: a comparative study in a canine aortoiliac model.

In vivo stability of a new small-caliber polyurethane graft (n8) was assessed in a canine aortoiliac model and compared to that of a conventional expanded polytetrafluoroethylene (ePTFE) graft (n8). Six months following implantation, marked aneurysmal dilatation to 230 +/- 80% (mean +/- SD) of the original diameter occurred in polyurethane grafts, while dilatation to 110 +/- 8% of the original diameter occurred in ePTFE grafts (p less than 0.005). Interval patency was 75% for each graft type. Luminal thrombus affected 59% of polyurethane graft surfaces compared to 22% of ePTFE graft surfaces (p less than 0.01). Qualitative examination of representative sections of polyurethane conduits demonstrated thick inner capsules with numerous small islands of graft material surrounded by macrophages and bands of mature fibrous tissue, in contrast to the thinner neointima and limited anastomotic pannus ingrowth observed in ePTFE grafts.

Animals↗

PubMed1991

Physical and blood-contacting properties of polyurethanes based on a sulfonic acid-containing diol chain extender.

Polyurethanes chain extended with N,N-bis (2-hydroxyethyl)-2-aminoethane-sulfonic acid (BES) were synthesized. The effect of the sulfonic acid group on the polymers' bulk, surface, and blood-contacting properties was evaluated by comparing the BES-based polymers with polyurethanes based on N-ethyldiethanolamine (EDEA). In addition, the effect of soft-segment polarity was addressed by comparing polyurethanes based on polytetramethylene oxide (PTMO) (MW = 1000) with polymers based on polyethylene oxide (PEO) (MW = 1000). The EDEA control samples had physical properties similar to a viscous fluid. The presence of the sulfonic acid group dramatically enhanced the degree of microphase separation and the mechanical strength of all the polymers. The more polar PEO soft segment resulted in polymers which were more phase mixed than the PTMO-based polyurethanes. Surface characterization studies revealed that in vacuum, all the surfaces were enriched in the polyether soft-segment phase. After 24-h equilibration in water, all the surfaces had similar surface polarities independent of the SO3H content. The canine ex vivo blood-contacting results showed that the sulfonic acid group in the PTMO-based polymers significantly reduced the number and activation of the adherent platelets. Fibrinogen deposition, however, increased with increasing sulfonic acid content. In contrast, platelet and fibrinogen deposition on the sulfonic acid-containing PEO-based polymers was greatly enhanced.

Adsorption↗

PubMed1991

In vivo biocompatibility of an aliphatic crosslinked polyurethane in rabbit.

A cage implantation technique has been adopted in a rabbit animal model to investigate the biocompatibility of an aliphatic crosslinked polyurethane based on hexamethylene diisocyanate (HDI). In this study, four cages are represented; the cage containing the candidate polyurethane material, biomedical grade polyurethane (Tecoflex), the commercial grade polyvinylchloride (PVC), and an empty cage which were implanted subcutaneously in rabbits. Exudates were aspirated from these cages at 4, 7, 14, and 21 days postimplantation. Exudates were analyzed for variations in proteins, cell counts, and extracellular enzymes. Results with the four types of cage implants showed that the candidate polyurethane caused an inflammatory response comparable to that caused by medical-grade Tecoflex and the empty cage control.

Alkaline Phosphatase↗

PubMed1992

Effect of sulfonation of segmented polyurethanes on the transient adsorption of fibrinogen from plasma: possible correlation with anticoagulant behavior.

The influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two-step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted in terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer-plasma "gel" hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anticoagulant activity on these materials.

Adsorption↗

PubMed2001

Enhanced degradation of naphthalene by immobilization of Pseudomonas sp. strain NGK1 in polyurethane foam.

A Pseudomonas sp. strain NGKI (NCIM 5120) capable of degrading naphthalene was immobilized in polyurethane foam. The naphthalene-degrading activity of the freely suspended cells was compared with that of immobilized cells in batches in shaken culture and in a continuous culture system in a packed-bed reactor. Increasing concentrations of naphthalene were better tolerated and more quickly degraded by immobilized cell cultures than by free cells. An initial naphthalene concentration of 25 mM was completely degraded by freely suspended cells (4 x 10(10) cfu ml(-1)) and polyurethane-foam-immobilized cells (0.8-1 x 10(12) cfu g(-1) foam cubes) after 4 days and 2 days of incubation, respectively. Free cells degraded a maximum of 30 mM naphthalene after 4 days of incubation with 50 mM naphthalene, and no further degradation was observed even after 15 days of incubation, whereas foam-immobilized cells brought about the complete degradation of 50 mM initial naphthalene after 6 days of incubation. Furthermore, with 25 mM naphthalene, the polyurethane-foam-immobilized cells were re-used 45 times over a period of 90 days without losing naphthalene-degrading activity. By contrast, with the same amount of naphthalene, alginate-, agar-, and polyacrylamide-entrapped cells could be reused for 18, 12, and 23 times over a period of 44, 28, and 50 days, respectively. During continuous degradation in a packed-bed reactor, foam-immobilized cells degraded 80 mM naphthalene at a rate of 150 ml(-1) h(-1). With the same flow rate and 40 mM naphthalene, this system operated efficiently and continuously for about 120 days, whereas the packed-bed reactor with alginate-, agar-, and polyacrylamide-entrapped cells could be operated only for 45, 40, and 60 days respectively. Thus, more efficient degradation of naphthalene could be achieved by immobilizing cells of Pseudomonas sp. strain NGK1 in polyurethane foam, rather than in the other matrices tested.

Cell Count↗

PubMed1989

Hydrophilic polyurethane versus autologous femoral vein as substitutes in the femoral arteries of dogs: quantification of platelets and fibrin deposits.

Hydrophilic, microporous polyurethane vascular prostheses displayed good mechanical characteristics and the behaviour in vitro was excellent. The in-vivo results were, however, disappointing. To obtain a better understanding of the phenomena involved in the acute and early thrombosis, we implanted the polyurethane graft in the canine left femoral artery and an autologous femoral vein in the right for 4 and 24 h. At 4 h, one polyurethane graft was totally occluded and the other two were close to complete occlusion; at 24 h, none was patent. On the other hand, all autologous veins were patent. The thrombotic matrix incorporating both platelets and fibrinogen, quantified by labelling, was anchored along the anastomotic lines. This study confirms that polyurethane occlusion is initiated by hyperplastic reaction, but does not explain why.

Animals↗

PubMed1994

Effect of polyol molecular weight on the physical properties and haemocompatibility of polyurethanes containing polyethylene oxide macroglycols.

The physical properties and haemocompatibility of polyurethanes containing polyethylene oxide (PEO) of varying molecular weights but constant weight fraction of hard segment are investigated. The PEO molecular weights studied were 600, 1450 and 8000. Analysis of polyurethane phase separation and crystallinity using dynamic-mechanical analysis and differential scanning calorimetry show that the degree of phase separation and crystallinity increase with polyol molecular weight, but level off at the highest molecular weights. The degree of water absorption increases substantially with increasing PEO molecular weight, levelling off at the highest molecular weight. Tensile data show a maximum in extensibility at a polyethylene glycol (PEG) molecular weight of 1450, while ultimate strength increases with increasing segment length. When the materials are hydrated, there is a significant drop in the modulus, ultimate stress and ultimate elongation. Dynamic contact angle measurements show that surface hydrophobicity decreases as the soft segment molecular weight increases. Using electron spectroscopy for chemical analysis (ESCA) to determine the surface composition of these polyurethanes, it was found that the hard segment content at the surface increases as the polyol block length decreases. The haemocompatibility of these polyurethanes was investigated in an ex vivo canine blood-contacting model. Only for the shortest block length studied, PEG-600, are differences in blood compatibility observed. This material was found to be the most thrombogenic. The PEG-1450 sample shows comparable blood compatibility to PEG-8000.

Animals↗

PubMed1995

Neutrophil-mediated degradation of segmented polyurethanes.

The biostability of polyurethanes was evaluated using a human neutrophil cell culture. The polymers were synthesized with 14C radiolabelled components incorporated into the polyurethane chain and the amount of radiolabel released during exposure to cells and medium was used as a marker for material degradation. The effect of diisocyanate, soft segment and chain extender chemistry on the susceptibility of polymer degradation was examined. All polymers showed a release of material into the tissue culture medium which was unrelated to the cells. A significant cell-dependent release of radiolabel-containing material was found from one of the polymers (a polyester urea-urethane, TDI/PCL/ED) which increased linearly up to 96 h. The polyether-containing polyurethanes showed no significant cell-mediated degradation under similar conditions as measured by radiolabel release. Scanning electron microscopy (SEM) showed that the cells adhered to the different polyurethanes. However, no effect of neutrophils on polymer structure could be detected by this technique. The cellular response to each polymer was evaluated by measuring release of elastase-like activity (ELA) into the tissue culture media. After 24h TDI/PCL/ED showed the highest levels of ELA in the tissue culture medium. When TDI/PCL/ED was incubated with commercial elastase in vitro, a significant release of radiolabel was found which was comparable to the amount of radiolabelled material released from this polymer in contact with the neutrophils in culture. No significant amount of radiolabel was released from the corresponding polyether material (TDI/PTMO/ED) under similar conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Biodegradation, Environmental↗

PubMed1996

Hybrid biomaterials based on the interaction of polyurethane oligomers with porcine pericardium.

Hybrid biomaterials have been produced by the interaction of polyurethane oligomers with both fresh and glutaraldehyde-fixed porcine pericardium. The hybrid biomaterials so formed were translucent with occasional white streaks and/or spots, had increased stiffness (to touch) but remained pliable. No shrinkage temperature was detected for fresh porcine pericardium hybrid up to 100 degrees C compared to porcine pericardium (approximately 67 degrees C) and glutaraldehyde-fixed porcine pericardium (approximately 87 degrees C). Amino acid analysis of the fresh porcine pericardium hybrid showed a reduction in lysine content after active isocyanate-terminated polyurethane oligomers exposure, indicating cross-linking between the polymer and tissue. Histological examination of the hybrid material shows a thin grey coating on both surfaces of the tissue, implying at least surface cross-linking of the tissue with polyurethane. The results suggest that fresh porcine pericardium can be reacted with active isocyanate-terminated polyurethane oligomers to produce hybrid biomaterials with covalent bonding.

Animals↗

PubMed1996

Physical and biological effects of a surface coating procedure on polyurethane catheters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphylococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

Adsorption↗

PubMed1991

Polyurethane film (Opsite) vs. impregnated gauze (Jelonet) in the treatment of outpatient burns: a prospective, randomized study.

As it has been shown that re-epithelialization of partial skin thickness wounds can be accelerated if the wound is kept moist, a prospective, randomized clinical study compared the water vapour-semipermeable polyurethane film, Opsite, with the conventional impregnated gauze dressing, Jelonet, in the treatment of outpatient partial skin thickness burns. Fifty-five patients were included: 30 were treated with the polyurethane film and 25 with the conventional dressing. The patients were followed at regular intervals until healing had occurred and were seen 3 months later for evaluation of residual scars and pigmentation. The burns treated with polyurethane films healed with a median of 10 days, while the conventionally treated burns healed with a median of 7 days (P greater than 0.05). Residual scars were noted in 21 per cent of the patients treated with polyurethane films and in 8 per cent treated conventionally (P greater than 0.05). Prophylactic methods should be publicly stressed since one-quarter of the patients were children of 3 years or less who were scalded by split hot liquids. Furthermore the patients' wounds were only briefly cooled before attending medical care. With small burns we advise that cooling should be prolonged until the pain fades then professional assistance should be sought.

Adolescent↗

PubMed2003

Clinical breakage, slippage and acceptability of a new commercial polyurethane condom: a randomized, controlled study.

Although latex remains the primary material for male condoms, a number of condoms made from synthetic materials have appeared in commercial markets in recent years. Published data on the safety and efficacy of these condoms is still limited, but nevertheless synthetic condoms do offer the user a wider choice and may encourage greater use of condoms for contraception and sexual transmitted infection prophylaxis. This paper reports on a study carried out in the Paris region of France on a new, commercial polyurethane condom marketed in Japan as Sagami Original and in Europe as Protex Original. A standard latex condom complying with the European standard for condoms (EN 600:1996) from the same manufacturer was used as the control in the study. The clinical breakage rate for the polyurethane condom was 0.6% (95% confidence interval 0.2-1.4%) compared to 1.3% (95% confidence interval 0.6-2.2%) for the latex condom. The difference was not statistically significant (chi(2) = 1.9, p = 0.168). Clinically significant slippage (complete slippage of the condom off the penis) was 1.1% (95% confidence interval 0.5-1.9%) for the polyurethane condom, compared to 0.5% (95% confidence interval 0.2-1.2%) for the latex; a difference that again was not statistically significant (chi(2) = 1.783, p = 0.182). The polyurethane condom was therefore equivalent to the latex condom in terms of clinical failure rate.

Adult↗