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At least 73 records · Page 4Linked to original sources

PubMed1991

Detection of toluenediamines in the urine of a patient with polyurethane-covered breast implants.

Breast prostheses are implanted for augmentation or during reconstructive surgery. One of the more commonly used prostheses is the polyurethane-sponge-covered silicone gel implant. Some clinicians are concerned about the safety of this product because the polyurethane foam disintegrates in vivo, and its subsequent fate is not known. Polyurethane is a polymer formed by reacting diisocyanates and polyols. This study indicates that the polymer sponge breaks down into its reactive monomers, 2,4- and 2,6-toluenediisocyanate, which are converted into their corresponding diamines. We present evidence of the excretion of the diamine metabolites in the urine of a patient implanted with polyurethane-covered prostheses.

Adult↗

PubMed1991

Heparinized polyurethane surface through ionic bonding of heparin.

Surface heparinization through an ionic bond is one of the methods used to improve polyurethane blood compatibility. Chains of poly(amido-amine), a tertiary aminic polymer capable of forming stable complexes with heparin, were either surface-grafted on polyurethane or interconnected with polyurethane chains using hexamethylenediisocyanate as cross-linking agent. In the latter case, a new material (PUPA) is formed with a heparin adsorbing capacity higher than poly (amido-amine) surface-grafted polyurethane. By changing the percentages of the components, different series of PUPA materials can be obtained with different physico-chemical properties. The ATR/FT-IR technique was used to characterize the new materials in the native and in the heparinized state. PUPA solution was used to coat commercial biomedical devices and they were also characterized physicochemically using ATR/FT-IR.

Animals↗

PubMed1989

[Experimental pancreatic duct occlusion with polyurethane].

Pancreatic transplantation requires an effective method to manage exocrine secretion. A new technique to eliminate the exocrine function of the pancreas by obstruction of the duct with polyurethane was investigated in terms of function, outcome and morphology. Polyurethane is an alcoholic solution of block copolymers with the property of polymerizing within 5-10 min. In this study the in-situ pancreatic tail model in dogs was utilized, the pancreatic duct was cannulated and injected with 2-3 ml of polyurethane. As a result, complete atrophy and fibrosclerosis of the exocrine tissue was obtained leaving islets well vascularized and functioning for the entire experimental periods. All animals remained normoglycemic and showed normal K-values. Amylase levels were found to be maximally elevated at 24 h and returned to normal within 2 weeks after duct occlusion. Insulin, glucagon and somatostatin levels remained normal. Because of its ability to effect a complete occlusion of the pancreatic ducts with subsequent atrophy of the exocrine gland and without notable disturbance of endocrine function, we feel that polyurethane solution is superior to previously used materials for this purpose.

Animals↗

PubMed1988

Polyurethane implants: a 6-year review of 416 patients.

The author reviews 6 years of experience and 416 patients in whom polyurethane implants were used for augmentation and reconstruction of the breast. As with many other plastic surgeons, early use was confined to "salvage cases." Owing to the impressive results, use was extended to routine augmentation. Polyurethane implants are now used exclusively for aesthetic breast surgery. Results are evaluated for replacement of gel capsules and simple and radical mastectomy reconstruction. Gel capsules (Baker stages III to IV), in which prostheses were removed and replaced with polyurethane-covered implants, improved in 29 of 32 patients (87 percent). For reconstruction, placement of polyurethane implants in unscarred situations gives far superior results than following repeated procedures. The incidence of infection is no higher than with gel implants. Removal without capsulectomy was not a problem in most instances. However, on two recent occasions capsulectomy was extremely difficult.

Breast↗

PubMedDate not supplied

[Enzymic splitting of polyurethanes containing dipeptide links in the main polymeric chain].

The paper deals with the proteolytic enzyme induced destruction of new types of segmented polyurethanes, the main chain of which contains dipeptides links: L-phenylalanyl-L-serine and glycyl-glycine. It is established that the chymotrypsin treatment decreases essentially the molecular mass of polyurethane containing the Phe--Ser links and does not affect the molecular mass of polyurethane with Gly--Gly links. Trypsin has no effect on the both types of polymers. Specificity of the chymotrypsin effect on the polymers is confirmed by the data of IR-spectroscopy. Destruction of the both types of segmented polyurethanes, mainly of the dipeptide fragments, is observed when the polymers are implanted into the animal organism.

Chymotrypsin↗

PubMed1994

The effects of soft segment structure on the fatigue crack propagation of model polyurethanes.

The present work is a study of the effects of soft segment molecular weight and chemical structure on the fatigue crack propagation of model copoly (ether-urethane-urea)s (PEUU). The PEUU were synthesized using polypropylene glycol (PPG), polytetramethylene glycol (PTMG), and polyethylene glycol (PEG) as the soft segment component. The number average molecular weights of the polyethers were within the range of 1000-2000. Methylene bis (4-phenylisocyanate) (MDI) and ethylene diamine were used as the diisocyanate and the chain extender, respectively. The cyclic loading experiments were carried out using a computerized film stretcher that can conduct sinusoidal operation at a constant strain amplitude, strain rate, and frequency. The Rivlin-Thomas tearing energy, T, and the fatigue crack propagation (FCP) rate were selected to characterize the fatigue behavior of the model polyurethanes. An empirical equation was applied to define the fatigue properties of model polyurethanes and to evaluate the fatigue resistance. To investigate the effect of molecular variables on the FCP, the morphological changes caused by structural differences and cyclic stress were determined using dynamic viscoelastometer (Rheovibron), Small Angle X-ray Scattering (SAXS), and Fourier-Transform Infrared (FT-IR) spectroscopy. Mooney-Rivlin plot was used to determine the crosslink density variation. In addition the orientation behavior at the crack tip was characterized by IR dichroism technique using a polarized FT-IR microscope. The results indicated a reasonable relationship between the FCP rates and the hard segment content, crosslink density, and deformation property at the crack tip. However, the initial stage of phase separation and domain disruption behavior did not show a good correlation with the FCP properties of model polyurethanes. Among the model polyurethanes tested, the PEUU with PTMG (Mn = 1000) exhibited the best fatigue resistance at given test condition.

Biocompatible Materials↗

PubMed1990

Unna's boot vs polyurethane foam dressings for the treatment of venous ulceration. A randomized prospective study.

Recent reports have suggested that polyurethane foam dressings provide a more rapid and comfortable healing of venous stasis cutaneous ulcerations than standard semirigid impregnated gauze dressings. This multi-institutional study consists of a randomized, prospective comparison of 36 consecutive patients who were treated with either polyurethane foam dressings (group 1, n = 17) or Unna's boot (group 2, n = 19) for venous ulceration of the lower extremities. Ulcer size ranged from 6.0 to 270 cm2 (mean, 32.2 cm2) for group 1 and 0.2 to 600 cm2 (mean, 76.0 cm2) for group 2. Nine (52.9%) of 17 group 1 patients withdrew from the study due to wound odor, while there was 100% compliance in group 2. Overall wound healing was superior in group 2 (18 [94.7%] of 19) as compared with group 1 (7 [41.2%] of 17) (chi 2 = 8.2). The rate of healing was also better in group 2 (0.5 cm2/d) than in group 1 (0.07 cm2/d). Contrary to published European trials, impregnated gauze dressings exhibited superior treatment results when compared with polyurethane foam dressings in the current study.

Bandages↗

PubMed1986

An unusual type of keratopathy observed in polyurethane workers and its reproduction in experimental animals.

We have reported two cases of keratopathy in polyurethane workers that appear to be identical to those described by previous authors. We have been able to produce similar findings in the corneas of cats by exposing the eyes of anesthetized animals to the vapor of two of the amines used as catalysts in polyurethane manufacture. We were unable to reproduce these results with toluene diisocyanate. Therefore we support the previous suggestion that the amine catalysts are responsible for the distinctive keratopathy in polyurethane workers. We are unable to substantiate the claim that toluene diisocyanate is responsible for this phenomenon.

Adult↗

PubMed1983

Fracture of a polyurethane cardiac catheter in the aortic arch: a complication related to polymer aging.

An undated Cordis Ducor polyurethane coronary catheter fractured and separated in the aortic arch during a cardiac catheterization, and was removed with an intravascular retriever. The recovered specimen appeared brittle, prompting an investigation of the effects of aging on the tensile strength of 91 polyurethane catheters manufactured by Cordis and the United States Catheter and Instrument Company (USCI). Cordis catheters have stable tensile strength for five years from manufacture, but then deteriorate substantially by seven years, particularly at the bond between the catheter tip and the stainless steel-reinforced catheter body. The deterioration is associated with the microscopic appearance of deep cracks in the catheter lumen wall. USCI catheters showed a modest but significant loss of tensile strength by three years after manufacture at the catheter bond. It would seem prudent to place a three-year expiration date on USCI polyurethane catheters, similar to those already on Cordis catheters.

Adult↗

PubMed1982

Urinary excretion of 5-hydroxyindolacetic acid in occupational exposure to polyvinyl chloride and polyurethane foams.

The effect of plastics as polyurethane foams and polyvinyl chloride on the metabolism of tryptophan was investigated by determining the concentration of 5-hydroxyindoleacetic acid (5-HIAA) as its metabolic end product excreted in the urine. Investigation of persons occupationally exposed to polyurethane and polyvinyl chloride showed that these plastics inhibit the metabolism of tryptophan, causing increased excretion of its easily measurable metabolite 5-HIAA. This fact points to the possibility of practical use of this laboratory test which, together with other biological parameters, could improve methods for early detection of occupational exposure to polyurethanes and polyvinyl chloride.

Environmental Exposure↗

PubMed1985

Heparinized polyurethanes: in vitro and in vivo studies.

Heparin immobilization chemistry using alkyl spacer arms was adapted to optimize yield on polyurethane (PU) surfaces. The resultant biological activity of immobilized heparin (HI) was examined in vitro and in vivo, and compared with a heparin releasing (HR) system. Immobilized heparin retained its ability to bind and inactivate thrombin and Factor Xa; nonspecific coagulation factor binding was insignificant. Such activity cannot be attributed to the leakage of improperly bound heparin. Immobilized heparin-polyurethane catheters implanted in canine femoral and jugular veins for 1 h periods exhibited significant reduction in thrombus formation compared with untreated PU contralateral controls. Polyurethane catheters coated with a 9% heparin dispersion in PU (HR) system provided even greater improvement in antithrombogenicity.

Animals↗

PubMed1987

Surface characterization of heparin-complexing poly(amido amine) chains grafted on polyurethane and glass surfaces.

Poly(amido-amine) chains grafted onto polyurethanes and glass form stable complexes with heparin yielding potential nonthrombogenic surfaces. The characterization of the surfaces, and the product of each chemical reaction including final heparinized surfaces, has been studied by contact angle data and scanning electron microscopy (SEM). Air in water, octane in water, and drop-on-plate contact angle data were used to estimate surface (gamma sv) and interfacial (gamma sw) free energies. Solid-water work of adhesion (Wa) and its dispersive (Wda) and polar (Ipsw) components were calculated for all studied surfaces. It has been found that the viscosity of polyurethane solution used for film casting influences wetting properties of these films. It has also been found that a direct correlation exists between the Ipsw/Wda values and the degree of coverage of the surfaces by cellular deposits after their exposure to platelet-rich plasma. Final heparinized polyurethane and glass materials are hydrophilic, their Ipsw/Wda ratio is high, and little or no cellular deposit is observed on their surfaces.

Biocompatible Materials↗

PubMed1987

Effects of alkyl grafting on surface properties and blood compatibility of polyurethane block copolymers.

In order to probe the factors which affect the interaction between the surface of a multiphase polyurethane material and blood, a series of butanediol-chain-extended polyetherurethanes was synthesized. These polyurethanes contained different levels of phase separation, produced by systematically varying the hard segment chemical structure by grafting ethyl and octadecyl groups to the urethane nitrogen atom. Surface characterization using high vacuum, air-equilibrated, and water-equilibrated methods was performed. A canine ex vivo arteriovenous series shunt was used to monitor initial platelet and fibrinogen deposition on these polymers. The ex vivo response to these materials, along with contact angle and ESCA surface chemistry, was found to vary with the degree of alkyl derivatization. This study demonstrated that an increase in the degree of phase separation and also the incorporation of long chain (C18) alkyl groups can affect surface properties and improve the short-term blood compatibility of the underivatized polyurethane.

Animals↗

PubMed1989

Establishment of a neovascular bed in a collagen-impregnated polyurethane sponge.

A technique for promoting vascularization of a polyurethane sponge is demonstrated in the present study. Collagen-impregnated polyurethane sponges (Hypol, 2002) Foamable Hydrophilic Prepolymer (FHP) were implanted in the femoral fossa of rats for 1 day to 6 weeks. The ligated femoral artery/vein was pulled through the sponges to facilitate more complete neovascularization. Light-microscopic evaluation of the implanted sponges revealed that significant vascularization had occurred by the seventh day of implantation, and was maximal by the fourth to sixth week. Sponges containing collagen had a more thorough vascularization process than sponges without collagen, perhaps due to a more uniform pore size as demonstrated by scanning EM. Time course studies suggested that the artery/vein pull-through enhanced the development of the neovascularization process in the center of the sponges. We conclude that significant vascular tissue in-growth can be developed in polyurethane sponges and that both collagen and centrally placed blood vessels help promote the vascularization process. Potential applications could extend to a variety of bioartificial systems including endocrine or hepatic transplantation, soft-tissue prosthetic materials, bone grafts, or drug delivery systems. Further studies would be useful in providing additional information on the factors promoting neovascularization, and on the potential applications of this methodology using the present or similar biomaterials.

Animals↗

PubMed1990

Characterization of alkyl grafted polyurethane block copolymers by variable takeoff angle x-ray photoelectron spectroscopy.

Variable takeoff angle x-ray photoelectron spectroscopy was used to determine the surface composition of five polyurethane block copolymers. The high-resolution C1s spectra from all five polyurethane samples had peaks at binding energies of 285.0, 286.5, and 289.5 eV, which are consistent with the presence of hydrocarbon, ether, and urethane carbon species. Both the measured elemental compositions at the low takeoff angles (deepest sampling depths) and the calculated elemental compositions for depths greater than 15 A generally showed good agreement with the expected bulk compositions. The outer 15 A of the surface of all five samples was depleted in the nitrogen-containing hard segment. For the base polyurethane sample in this series, an enrichment of the poly(tetramethylene oxide) soft segment and the presence of an organic silicone impurity were detected. Doubling the chain length of both the hard and soft segments resulted in a further decrease of the hard segment concentration in the outer surface of the sample. The grafting of C2 and C18 alkyl groups onto 10 or 20% of the urethane linkages resulted in an increase in the percentage of aliphatic carbon species present on the surface. In the case of the C18-alkylated material, the presence of alkyl chains at the surface was inferred using contact angle measurements.

Biocompatible Materials↗

PubMed1992

Postadsorptive transitions in fibrinogen adsorbed to polyurethanes: changes in antibody binding and sodium dodecyl sulfate elutability.

Residence time-dependent changes in fibrinogen after adsorption to six different polyurethanes were examined by measuring polyclonal antifibrinogen binding to the adsorbed protein. The amount of adsorbed fibrinogen that could be eluted by sodium dodecyl sulfate (SDS) was also measured. Baboon fibrinogen was first adsorbed from dilute plasma to the polymers, which were then stored in either buffer or buffered albumin solution prior to testing. Subsequently, the amount of antifibrinogen bound by the adsorbed fibrinogen was measured using a direct enzyme linked immunosorbent assay (ELISA). Alternatively, the surface with the adsorbed fibrinogen was soaked in a 3% SDS solution, and the amount of retained 125I-radiolabeled fibrinogen was measured. With increasing residence time, decreases in both antibody binding and the SDS elutability of the adsorbed fibrinogen occurred, but the rate of change was dependent on the polyurethane to which the fibrinogen was adsorbed. In addition, the antibody binding per unit of adsorbed fibrinogen, when measured immediately after the adsorption step, varied by approximately a factor of 3 among the various polyurethanes. When the protein-coated surfaces were stored in buffered albumin solution rather than buffer, the decrease in the reactivity of fibrinogen with residence time did not occur on some of the surfaces. This study shows that the chemical properties of the adsorbing surface influence the rate at which adsorbed fibrinogen undergoes change. The significance of the polymer-dependent changes in adsorbed fibrinogen with respect to blood reactions with polymers is discussed.

Adsorption↗

PubMed1992

Theoretical analysis on cell size distribution and kinetics of foreign-body giant cell formation in vivo on polyurethane elastomers.

The nature of in vivo leukocyte adhesion and foreign-body giant cell (FBGC) formation on polyurethanes was studied through theoretical and statistical analyses in terms of cell size distribution, density changes, and kinetics of FBGC formation. The results showed that the size distribution of FBGCs followed a "most probable" distribution. During FBGC formation, the densities of FBGCs changed with time. At an early stage, the number of FBGCs increased with time to a maximum at the expense of macrophages. As more FBGCs were formed and less macrophages were present, the fusion of FBGCs among themselves became significant. This, in turn, caused a gradual decrease of FBGC density with time. The rate of FBGC formation was characterized by a rate constant that represented certain characteristics of cell fusion and FBGC formation and the density of initial FBGC-forming macrophages that were a small fraction of leukocytes adhering to the surface. The direct correlations of surface cracking and pitting and adherent FBGCs demonstrated the influence of phagocytic actions of FBGCs on the biostability of implanted polyurethanes. While the cracking was thought to be caused by oxidative degradation facilitated by oxygen ion/radical release of FBGCs, the pitting appeared to result from the Methacrol 2138F aggregates diffusing out of the polymer in an acidic microenvironment under FBGCs, which in turn could be enhanced by the surface degradation and cell phagocytosis. The added Santowhite powder in polyurethane had a significant influence on FBGC formation: It reduced FBGC density and rate of FBGC formation by reducing leukocyte adhesion and the number of macrophages participating in FBGC formation.

Amines↗

PubMed1994

Antithrombogenicity of lumbrokinase-immobilized polyurethane.

Lumbrokinase is a potent fibrinolytic enzyme purified from the earthworm, Lumbricus rubellus. We immobilized 18 IU/cm2 of lumbrokinase to polyurethane using maleic anhydride methylvinyl ether copolymer (MAMEC) as an enzyme carrier, and the proteolytic and fibrinolytic activities of immobilized lumbrokinase were assayed. Immobilized lumbrokinase retained about 34% of its activity, compared with soluble lumbrokinase activity. Immobilized lumbrokinase showed stability against thermal inactivation and degradation and within a various pH range. The optimal pH of immobilized lumbrokinase shifted 1.0 pH unit upward compared with soluble enzyme. Upon exposure to the human whole blood, less amount of 125I-fibrinogen was adsorbed to lumbrokinase-immobilized surface than to the polyurethane control surface. The lumbrokinase-immobilized surface showed less platelet adhesion than did the MAMEC-grafted surface. At the early stage of platelet adhesion, the number of adhered platelets increased on the lumbrokinase-immobilized surface with increasing time; yet, the platelet number drastically decreased on the lumbrokinase-immobilized surface after 80 min incubation. This suggests that lumbrokinase-immobilized polyurethane digested the adsorbed fibrinogen and inhibited platelet adhesion on the surface, probably by inhibiting fibrinogen adsorption to be highly antithrombogenic. Clinical applications of this material to artificial organs should be developed in the near future.

Adsorption↗