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At least 19 recordsLinked to original sources

PubMed1978

Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. I.

The evaluation of the efficiency of polymer additives with special emphasis on uv absorbers and antioxidants in polyurethane elastomers has been completed. Aliphatic polyurethanes were chosen for this study because their properties closely relate to the requirements of maxillofacial prosthesis. The polyurethane elastomers were either synthesized by ourselves or formulated according to the manufacturer's recommendation. Eleven different types of uv absorbes, coupled with one antioxidant, were incorporated into the polyurethane systems. The Atlas twin-lamp carbon arc Weatherometer was used as the source of uv. The samples were periodically withdrawn for examination of yellowing and tackiness. It was found that, although the incorporation of uv stabilizers enhanced the uv resistance of polyurethanes, the problem of tackiness resulting from uv aging was not solved satisfactorily. The phenomenon of yellowing, however, was significantly improved, mainly due to the aliphatic structure of polyurethanes. The most promising uv absorbers are Tinuvin 770 and the combination of Tinuvin 328, ZnO, and an antioxidant. Their effectiveness in other polyurethane systems is not known and further research is underway to explore this field. Hopefully, these findings will greatly assist the successful application polyurethane elastomers in maxillofacial prosthesis.

Biocompatible Materials↗

PubMed1978

[Studies on orthodontic polyurethane ringlets. (Part 1) Examination of its physical properties (author's transl)].

The purpose of this study was to develop orthodontic ringlets from polyurethane which have maximum flow resistance. The two types of polyurethane involved were thermoplastic and thermosetting polyurethane. The former included Paraprene 22, 25, 4805 + 4806, Biomer, Elastollan 585 (E-585) and improved Elastollan 590 (E-590). Thermosetting type incorporated Adiprene, Loyler 2170, Colonate 4080 and DC-4978. Using these materials as its base, a ring device was developed. Under two conditions, tests were conducted for tensile strength, aging effects on 50% and 100% modulus and permanent elongation. One group was stored in air at 20 degrees C and the other in water at 37 degrees C. The results were as follows; It was found that the thermoplastic polyurethane possessed high tensile strength. However, the modulus upon aging resulted in a lower reading with the exception of E-590 and Biomer. In the thermosetting polyurethane group, most of the rings except DC-4978 broke down during storage at 100% elongation in water at 37 degrees C. In the case of DC-4978, there was maximum flow resistance. Upon comparing it with E-590 and Biomer, it appeared that DC-4978 was the most effective for orthodontic purposes.

Elasticity↗

PubMed1978

Tissue reactions to breast implants coated with polyurethane.

The histological features noted in the capsules from 7 polyurethane coated silicone breast prostheses are described. The polyurethane provoked a definite foreign body reaction and was slowly degraded, with some particles ejected from the capsule into the surrounding tissues. Separation of the polyurethane coating from the silicone prosthesis and the degradation of the polyurethane took about two years. Another much more resistant foreign material was found to occur in conjunction with the polyurethane in the capsules. It may be an adhesive or flakes off the silicone shell. Vacuolated spaces were noted in the inner layers of 3 capsules; it was assumed that they contained liquid silicone.

Breast↗

PubMed1978

Physical and mechanical behavior of polyurethane elastomer formulations used for facial prostheses.

The initial results of this study of the physical and mechanical behavior of polyurethanes used for facial prostheses are presented. The parameters studied were surface hardness, modulus of elasticity (M), strength (S), percentage of elongation, and S/M ratio. Results showed that the physical and mechanical behavior of the polyurethanes can be altered by variations in the basic composition of the material accomplished through changes in the ratio of Part A to Part B and by the addition of catalysts. Properties of compositions with low quantities of Part B (isocyanate) and no catalyst reached or approximated those parameters proposed as ideal goals to simulate living tissue. When preparing polyurethane material, proper mixing is essential to avoid entrapment of air and phase separation of the catalyst. These conditions, which may render the prostheses less durable, are masked by the addition of colorants in the prearation of a sample for clinical application.

Chemical Phenomena↗

PubMed1992

Is polyurethane lead insulation still controversial?

A controversy arose some 10 years ago over the reliability of polyurethane lead insulation. On the basis of one of the longest standing and largest databanks worldwide, the authors compare the cumulative survival of several thousand polyurethane, standard silastic, and high-performance silastic electrodes as it pertains to the failure criterion described as insulation degradation. With the possible exception of the Medtronic 6972 (Medtronic, Inc.) electrode, polyurethane electrodes have a 100% reliability at 84 months, which is similar to silastic electrodes.

Databases, Factual↗

PubMed1976

Scanning electron microscopy of surface irregularities and thrombogenesis of polyurethane and polyethylene coronary catheters.

Following routine coronary arteriography, surface irregularities and thrombogenesis of the inner and outer wall of six Ducor polyurethane and six RPX polyethylene coronary catheters were studied by scanning electron microscopy. Polyurethane catheters had rough and highly irregular external and internal surfaces. All catheters showed adherent thrombi on their external surface. The internal surface of three catheters showed evidence of thrombosis. Polyethylene differed from polyurethane in several respects. Although the external surface had an irregular and wavelike appearance, the internal surface was smooth and regular. Two polyethylene catheters showed thrombi on their external surface. The internal surface of one catheter showed single platelets in one area. These results confirm recent reports showing that internal and external surface irregularities play a major role in the initiation of thrombosis in and on intravascular catheters. They stress the need for high quality catheter materials with smooth and regular surfaces in the prevention of thromboembolic complications from coronary arteriography.

Adult↗

PubMed1977

[Skin wound granulation from contact with synthetic foil of teflon-polyurethane type].

When a plastic-foil consisting of teflon-polyurethan foam is applied to ulcer cruris and to polyurethan foam is applied to ulcera cruris and to combusted skin, pronounced granulation and formation of new capillaries and collagen fibers are observed in the contact area. The tightly adhering foils are tolerated by the wounds for more than 40 days with continous granulation. An adverse reaction against the foreign material and development of eosinophils and giant cells is not observed, though the polyurethan-foam of the foil was burst by the ingrowing granulation tissue. When the wound surface is clean, change of the dressing with this foil is necessary only every second or third day.

Bandages↗

PubMedDate not supplied

Polyurethane foam in postoperative casts.

One-half inch thick polyurethane foam is recommended for use in postoperative casts to avoid complications seen with postoperative swelling. The polyurethane is placed over the operative area, over the dorsum of the foot, and the anterior surface of the leg. The use of polyurethane foam in the postoperative cast not only avoids the necessity of having to split the cast in many instances but the foam also constitutes a compression dressing. If splitting of the postoperative cast should become necessary, the foam protects the skin.

Casts, Surgical↗

PubMed1977

Polyurethane foam (Bentley) micropore blood transfusion filter: filtration characteristics.

Stored human blood of varying age was passed through polyurethane foam (Bentley) micropore blood transfusion filters. Passage through these filters resulted in decreased screen filtration pressure (SFP) of the blood and increased filter weights. Numerous microaggregates were removed and SFP returned to normal after filtration. Occlusion of the filter occurred after passage of only 2 units of whole blood. On the basis of this research, we conclude that polyurethane foam (Bentley) micropore blood transfusion filters are effective in removal of microaggregates from stored human blood. Because the filtering capacity is not great, it is recommended that when these filters are used during transfusion a new filter be used for each unit of blood administered.

Blood Preservation↗

PubMed1977

Interactions between segmented polyurethane surfaces and the plasma protein fibrinogen.

Surfaces of a segmented polyurethane were varied by casting on poly(ethylene terephthalate) (PET) and glass substrates, and were characterized through infrared-attenuated total-reflection spectroscopy (ATR). Surfaces cast on glass substrates showed a higher content of polyether segments, whereas those cast on PET contained a higher relative concentration of aromatic segments. Adsorption, and possible conformational changes of fibrinogen, were found to be more substantial on polymer surfaces having a higher content of polyether segments. It is concluded that the relatively good blood compatibility of segmented polyurethanes is partly due to the presence of peptide-like bonds on aromatic segments.

Adsorption↗

PubMed1979

ESCA studies of surface chemical composition of segmented polyurethanes.

Surface chemical analysis of two commercially available polyurethanes, i.e., Avcothane and Biomer was carried out by electron spectroscopy for chemical analysis (ESCA). The depth which is subject to analysis is in the range of 50-100 A. The variables studied in this study are the difference in exposure to air or to the mold substrate during the solvent casting process. Model compounds such as a pure polydimethylsiloxane, polyether soft segment and hard segment copolymer were used to identify and assign various ESCA peaks. The air facing surface of Avcothane which is the blood contacting surface is found to be covered mostly with polydimethylsiloxane polymer, with a small amount of polyether soft segment mixed with silicone. Therefore, the hard segment of the polyurethanes is hidden beneath the blood contact surface in Avcothane. In Biomer films, the air facing surface contains a greater concentration of polyether soft segment than the substrate surface. These results are consistent with our previous results obtained by Fourier transform IR internal reflection and Auger electron spectroscopy.

Carbon↗

PubMed1979

Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. II.

The effect of selected UV stabilizers on the stability of mechanical properties of a polyurethane material, Calthane ND2300, was evaluated. The addition of UV stabilizers prolonged the service life of the systems studied but did not achieve completely satisfactory results. The tensile strength and modulus of elasticity decreased after extended exposure to UV. The rate of decrease, however, was much less for the specimens with UV stabilizers. The polyurethane system that contains a mixture of a UV stabilizer and an antioxidant is considered to be the best of the groups tested, in terms of the percentage of retention of tensile strength and modulus of elasticity. It was also found that elongation at break was increased when the duration of UV aging was increased. This phenomenon occurred in all the systems, with or without UV stabilizers, and can be understood in terms of the concepts of the fragmentation of macromolecules that resulted from UV aging. The physical appearance in conjunction with mechanical property tests are needed to ensure the successful performance of any UV stabilizer.

Chemical Phenomena↗

PubMed1976

[Development and application of a new polyurethane plastics support bandage (author's transl)].

Experiences with a newly developed plastics support bandage on 1007 patients are reported. A polyurethane hard foam composition developed specially for medical purposes was used, which is created by blending the two components A (polyol) and B (isocyanate). The principle of our support bandage lies in the fact that after being mixed in a 1:1 ratio, the two highly viscous components are packed into a cotton stocking having a high transverse elasticity. After being rolled out to the desired thickness, the stocking is wrapped around the extremity which it is to support, where it hardens out into a polyurethane hard foam composition. By reason of the moisture content of the scoured cotton stocking, a 1 to 2 mm thick layer of foam forms in the contact region and renders any further padding unnecessary. Correspondingly, by using a double chamber stocking, circular bandages have been produced which can be removed, by means of incorporated zip and interengaging hook fasteners. Reclining shells, abduction bandages and body corsets can be made in the same way. The physical properties of the support bandage are illustrated: apart from its low weight, the bandage is particularly advantageous by reason of its high strength, insensitivity to water and ideal permeability to X-rays. The support bandages are easily made up and entail negligible cost.

Braces↗

PubMedDate not supplied

Polyurethane elastomer as a possible resilient material for denture protheses: a microbiological evaluation.

A polyurethane elastomer was microbiologically evaluated in vitro for its potential use in resilient denture liners. Specimens were immersed in suspensions of ten selected oral microorganisms; this was followed by viable cell counts at intervals during a 16-week period. Results indicated that the polyurethane neither supported the growth of the organisms nor was it degraded.

Candida↗

PubMed1975

Carcinogenesis from polyurethans.

Seventeen polyurethans, containing various substituent groups, and a polyethylene were implanted i.p. in groups of male black Bethesda rats and were evaluated for carcinogenesis over a 2-year period. Thirteen of the polyurethans and the polyethylene were similarly studied in females. Tumor development in these animals was expressed in terms of the incidence in the at-risk population, and the tumorigenic latent period was approximated for each sample. Twenty months after implantation, the relative tumorigenicity (area under the corrected cumulative tumor mortality versus time curve) in the males ranged from 0 (for the unimplanted controls) to 6.18 (for Y-238); for female rats this range was 0.29 (for unimplanted controls) to 5.72 (for Y-238). Estimated latent periods in the males ranged from 5 months (for Y-304) to 16 months (for Y-303), and 22.5 months for the unimplanted controls; for the females, the range was from 9 months (for Y-290) to 13.5 months (for Y-217), and 14 months for the unimplanted controls. The relative tumorigenicity of each sample was also compared to its in vitro activation energy for thermal decomposition. These data are discussed in terms of solid-state versus chemical carcinogenesis.

Animals↗

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↗