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At least 613 records · Page 34Linked to original sources
PubMed1985

[Polyurethane positioning devices for radiotherapy].

A simple and cheap method is described for the manufacturing of individual positioning aids made of foamed polyurethane. Some examples are given to demonstrate the applicability of these positioning aids for the irradiation of different body regions. The reproducibility of the radiation field in the head and neck area was investigated with and without positioning aid. It was proved that the field is adjusted more exactly when positioning aids are applied. The dosimetric investigations performed showed a negligible influence of foamed polyurethane on the radiation quality. So the positioning aids could be left within the radiation field when drawing the field borders.

Humans↗
PubMedDate not supplied

[Production and properties of trypsin immobilized on a polyurethane matrix].

Two methods were used to immobilize trypsin on the polyurethane carrier on the basis of toluylenediisocyanatepolyoxypropylene glycol due to interaction between the lyzine free amino groups and the enzyme arginine guanidine group and the prepolymer isocyanate group. The amount of the enzyme chemically bound by the two methods is about 50 and more than 70%, respectively. The substrate specificity of the initial and washed samples of the immobilized trypsin was studied with respect to three highly molecular substrates with different molecular weight and different charges--protamine, casein, hemoglobin. It is shown that independently of the method of binding the activity of the immobilized trypsin is the highest with respect to hemoglobin and is the lowest with respect to protamine. The samples of trypsin immobilized on the polyurethane carrier may be used in biology and medicine when creating the prolonged forms of the enzymic preparations.

Caseins↗
PubMedDate not supplied

[Growth of rat fibroblasts in tissue culture as affected by trypsin immobilized on polyurethane substrates].

The growth of fibroblasts of the rat subcutaneous tissue was studied as affected by different doses of trypsin, free and bound, on polyurethane substrates. The method of tissue culture provides essential criteria for estimating the degree of bioincompatibility of polymeric alloimplants in particular when immobilizing biologically active substances on them. Trypsin adsorbed on the polyurethane substrate diffusing gradually into the culture medium is established to inhibit the cell growth. Chemically bounded trypsin in the composition of the polymeric matrix at the early stages of cultivation stimulates for a long time the division of fibroblastic elements and further accelerates their degeneration. It is shown that on polymeric substrates containing no trypsin, the growth character and dynamics of the fibroblastic elements are similar on the whole to these indices for cultures grown in the plasm clot without the substrate.

Animals↗
PubMed1979

[Comparative evaluation of biodestruction of polyurethanes synthetized on the basis of simple and complex polyesters].

In model liquids and experimental animals (rats, rabbits) with the aid of physico-mechanical and histological methods (using interferentially polarizating microscopy) a comparative evaluation was made of the biodestruction of polyurethanes from synthetized simple and complex polyesters. The tissue reaction to intra-abdominal, intramuscular and subcutaneous implantation of perforated stripes of A-19 and Nr. 36 polymer was moderate. Two weeks post-operative increased volumetric biodestruction of the polymers was observed. The course was different in various standards and depended upon the chemical structure of the polymers. Taking into account the slight macrophage tissue reaction, in counterdistinction to the significant volumetric biodestruction which envolved the entire width of the polymer strip, it is assumed that the destruction of the investigated polyurethane composition (adhesive KL-3) takes place by hydrolysis 3 to 6 months post-implant.

Animals↗
PubMed1977

[Role of macrophages and foreign body type giant cells in the biodestruction process of polyurethane adhesive tissue].

The biodestruction process of polyurethane adhesive was investigated in application to intestine anastomoses, wounds of skeletal muscles and surfaces of some internal organs. The polymer destruction was proved to be connected with the activity of giant cells of foreign body type and macrophages phagocyting the micromolecules of the adhesive. The presence of adhesive microfragments in macrophages and giant cells was ascertained on the basis of a method elaborated by the authors consisting in staining of the polyurethane adhesive with Sudan III-IV. Moreover, it was pointed out, that biodestruction products had no negative effect in the regeneration of nervous and muscle fibers.

Animals↗
PubMedDate not supplied

[Enzymic segregation of segmented polyurethanes containing sugar residues in the composition of the main chain].

It is shown that segmented polyurethanes with D-lactose and D-maltose residues in the main polymer chain are subjected to a specific effect of enzymes: beta-galactosidase and alpha-amylase, respectively. This leads to a decrease in values of characteristic viscosity and physicomechanical indices of polyurethanes after their incubation with the mentioned enzymes. The compounds obtained are subjected to acid hydrolysis, which confirms sugar residues in the main polymer chain.

Animals↗
PubMed1984

Thrombogenicity of central venous catheters: prospective study of polyethylene, silicone and polyurethane catheters with phlebography or post-mortem examination.

The thrombogenicity of polyethylene, silicone and polyurethane central venous catheters was compared in a prospective clinical, phlebographic and post-mortem study in 52 patients. The incidence of central venous thrombosis was high with polyethylene catheters (70%), but much lower with silicone (20%) and with polyurethane catheters (17%).

Catheters, Indwelling↗
PubMed1982

Colles' fractures treated by plaster and polyurethane braces: a controlled clinical study.

In a prospective randomized controlled trial polyurethane casts and traditional plaster-of-Paris braces were compared in 46 cases of Colles' fractures of the forearm. Secondary fracture dislocation, subjective inconveniences, and the need for secondary adjustment of the cast were recorded. No significant difference was observed in the two groups. In comparison with plaster the synthetic bandage is lighter, water repellent, and hardens faster, and as far as circular bandages are concerned, they have zippers. It is concluded that polyurethane braces are a good supplement to plaster-of-Paris bandage in such fractures and recommended in selected cases.

Adolescent↗
PubMed1982

Light microscopic and scanning electron microscopic findings on intravenous polyurethane catheters.

Tips of two different types of unused and used intravenous polyurethane catheters as well as heads of the corresponding needles for venipuncture, artificially cut surfaces and longitudinally cut parts were either directly mounted on stubs or previously fixed in 1% phosphate buffered glutaraldehyde, postfixed in 1% phosphate buffered osmiumtetroxyde (pH 7.4), dehydrated with acidified 2,2-Dimethoxypropane, dried in a critical point drying apparatus using CO2, mounted with silver paint on stubs and sputter coated with 15 nm gold. In general, the surface of polyurethane catheters is smoother than that of catheters manufactured out of other materials. Distance marks, when placed on the surface and parts of the catheter wall, containing radio-opaque admixtures show a very irregular arranged structure. It could be demonstrated, that these parts of the catheter wall as well as roughnesses, caused by the manufacturing process, are much more favourable for adhesion of formed elements of the blood and bacteria or spores than other areas of the wall. In addition occasionally extensive fibrin layers and contamination of the surfaces by denaturated plasma proteins were observed. For better compatibility and for prevention of endothelial lesions some advice is given to the manufacturers and the medical staff.

Bacteria↗
PubMed1981

Effects of polyurethane and polyimide thermal decomposition products on shock escape and avoidance behavior.

Thirty-six male Sprague-Dawley rats were exposed for 15 minutes to the decomposition products of either a polyurethane or polyimide foam while performing an unsignalled shock escape-avoidance task. These products were generated by placing 1 g samples of the foams on a conductive plate heated to either 435, 605, or 775 degrees C. The decomposition products and behavioral toxicity of the 2 foams varied differentially with test temperature. At the 2 lower temperatures, the decomposition products of polyurethane proved to be more behaviorally disruptive than those of polyimide, while at 775 degrees C the reverse was true. These results indicate that operant behavior technology brings a sensitivity to material testing which may prove quite useful for future assessments of potential behavioral toxicity.

Animals↗
PubMed1980

Polyurethane foam wheelchair cushions: retention of supportive properties.

The supportive properties of polyurethane foam wheelchair cushions change significantly during the first hours of use. Thus, cushions which initially appear to optimally distribute the patient's weight may not do so after a break-in period. To solve this problem, a cushion prestressing protocol has been devised which breaks-in the foam cushion prior to determination of the patient's pressure distribution. It was found that the useful life of these cushions is adversely affected by heavy static loading and high temperatures, and if allowed to rest, polyurethane foam cushions recover a portion of their original load-bearing properties.

Compliance↗
PubMedDate not supplied

Adhesion of silicone to polyurethane in maxillofacial prostheses.

Primers have been reported to increase adhesion between silicone elastomers and polyurethane liners used for maxillofacial prostheses. This study evaluated two primers, three polymerization methods, and seven primer reaction times to determine the conditions for optimum adhesive bond strength. The T-peel strength of specimens was determined as described in ASTM Standard D 1876-72. Failure modes were evaluated, and two-sample t tests and one-way ANOVA were used to compare means for significant (P < .05) differences. Bond strengths were significantly greater for polyurethane treated with primer 1205 rather than S-2260 regardless of the polymerization method or primer reaction time. Neither any single polymerization method nor single primer reaction time consistently yielded greater bond strengths.

Adhesiveness↗
PubMed1993

[Thrombogenicity of central venous catheters: comparison of two polyurethane catheters].

BACKGROUND: Thrombosis represents a possible catheter-related risk. Beside many endogenous and exogenous factors, the material as well as its condition do have a decisive influence on thrombogenicity. One factor of thrombogenicity is the surface of the catheter. Therefore, two different types of polyurethane catheters were compared according to their surface structure by electron microscopy. Furthermore, an in vivo testing should confirm a possible, different thrombogenicity. MATERIAL AND METHODS: A model with a single aperture at the catheter tip and a model with multiple apertures were tested. We compared the electron-microscopic pictures of specific areas which were expected to cause problems. Thrombogenicity in the vena cava inferior was tested in 20 rabbits. For statistical evaluation the Wilcoxon U test was used. RESULTS: Polyurethane catheters have a smooth and homogeneous surface inside and outside of the catheter. However, there are many production-related, qualitative differences in the morphology of the apertures. The model with multiple apertures and a closed catheter tip turned out to have a much more irregular surface compared to the model with a single aperture. In vivo testing showed that each catheter causes thrombosis, independent of the type. The catheter with multiple apertures proved to have no advantages as far as thrombogenicity is concerned; catheter-specific complications of this type are possible. Also, atraumatic insertion by means of Seldinger's technique is not possible using a catheter with a closed tip. CONCLUSION: The catheter with multiple apertures does not have any advantages to the catheter with a single aperture.

Animals↗
PubMed1996

[Small-caliber polyurethane arterial prosthesis: clinical and angiomorphological follow-up of 20 patients in a prospective study].

The five year patency rate for femoropopliteal vein bypass grafts is around 70% according to the literature. Patency rates for synthetic grafts (eg PTFE, Dacron) range between 43 and 57%. If a vein is not available there is a new polyurethane 6 mm artery substitute on the market, that has shown in vitro promising physical characteristics and good long term results after implantation in dogs. In a prospective, randomized trial the results of the new polyurethane graft (PUR) were compared with those of a Dacron graft of the same diameter. Included in the study were 20 patients with lower limb ischemia stage Fontaine II B, III and IV, 10 in each group. Patency rates, handling of the graft and complications were analysed. During the one year follow up 7 PUR grafts had to be changed due to recurrent bypass occlusion within the first 3 months. At the end of the year there were only one PUR-bypass but 8 Dacron grafts open. 5 PUR grafts were examined histologically and no morphological reason for the occlusion, especially no myointimal hyperplasia, was found. A special regard was brought to the arterial run-off in both groups. It was confirmed to be comparable with only slightly better data for the PUR group. The exact reasons for the astonishing bad results of the PUR graft for femoropopliteal above knee bypass cannot be explained in our study. Due to the unexpected high occlusion rate the study was stopped earlier then planned.

Aged↗
PubMed1996

Morphological observations of vas deferens occlusion by the percutaneous injection of medical polyurethane.

Histological observations of 20 occluded vas segments obstructed by the standard procedure of medical polyurethane-vas occlusion in 10 volunteers requesting vasectomy and of 20 vas segments with plugs removed from 10 vas-occluded men requesting vas reversal were carried out in order to elucidate the mechanism of vas occlusion by medical polyurethane (MPU). Twenty vas deferens in vasectomy group were ruptured, only a small amount of MPU elastomer remained within the vas lumen, most having leaked through to encircle the ruptured vas. Histomorphology of the removed vas segments from 10 vas-occluded men, who had undergone MPU-vas occlusion 4 years earlier, showed diffuse proliferation of connective tissue, fibrosis, or hyalinization of fibroplastic tissue and local infiltration of lymphocytes and macrophages. The vas lumen both proximal and distal to the plugs was completely blocked. Sperm granuloma, foreign body granuloma, proliferation of nerve fibers and local infiltration of lymphocytes were found in four vas-occluded men with painful nodules. These results suggest that the contraceptive mechanism of MPU-vas occlusion could be the result of secondary obstruction due to tissue proliferation by MPU irritation after the rupture of the vas deferens.

China↗
PubMed1997

Polyurethane heart valve durability: effects of leaflet thickness and material.

A flexible trileaflet polyurethane valve has been made by dip-moulding leaflets directly onto an injection-moulded frame. The durability of this value is, in part, determined by the thickness of its leaflets. Leaflet thickness is also a major determinant of hydrodynamic function. This study examines valves (n = 31) with leaflets made of a polyetherurethane (PEU, n = 22) or a polyetherurethaneurea (PEUE, n = 9), of varying thickness distributions. The valves were subjected to accelerated fatigue test at 37 degrees C and failure monitored. Leaflet thicknesses ranged from 60 to 200 microns. PEU leaflet thickness bore no relationship to durability, which was less than 400 million cycles. PEUE valves, in contrast, exceeded 800 million cycles. Durability in PEUE valves was directly related to leaflet thickness (r = 0.93, p < 0.001), with good durability achieved with median leaflet thicknesses of approximately 150 microns. Thus polyurethane valves can be made with good hydrodynamic properties and with sufficient durability to consider potential clinical use.

Biocompatible Materials↗
PubMed1999

Preparation and Morphology Studies of Core-Shell Type Waterborne Polyacrylate-Polyurethane Microspheres.

Core-shell type waterborne polyacrylate-polyurethane microspheres in which polyurethane acts as the shell and acrylic polymer as the core were prepared. Hydroxyethyl acrylate and adipic dihydrazide were used as cross-linking agents introduced to the ends of the shell molecular chains, and two kinds of cross-linked structures between the core and the shell were formed. The photon correlation spectroscopy studies indicate that all the microspheres present continuous particle-size distributions and their mean particle sizes are smaller than 200 nm. The transmission electron photographs reveal that there are obvious core-shell structures for the noncross-linked type microsphere particles and different cross-linked networks between the core and shell for the two kinds of cross-linked type microsphere particles. These microspheres possess excellent storage stability, water resistance, and coating properties. Copyright 1999 Academic Press.

Journal Article↗