PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Polyurethanes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
PubMed1991

New J-3 flexible-leaflet polyurethane heart valve prosthesis with improved hydrodynamic performance.

The aim of this new three-leaflet valve development was to design a leaflet with minimum membrane stresses during performance. This is achieved by manufacturing the valve leaflets shaped almost flat in a medium opening position. Thus, the leaflets have two stable positions, one with maximum opening area and the other with favorable stress distribution in the closed position. The transition between the two end positions is achieved through a two-dimensional rolling motion without buckling and with minimum membrane stresses (bulge forces). The manufacturing technique is dip-coating in polyurethane. Hydrodynamic evaluation of the J-3 valve in steady and pulsatile flow showed minimum pressure drop compared to other commercially available valves. Laser-Doppler-anemometry studies indicated very low shear stresses in the flow field downstream of the valve. In durability tests prototypes have reached lifetimes of up to 17 years. In conclusion, the J-3 valve shows superior hydrodynamic performance thereby reducing potential thrombus formation. Minimization of stresses within the valve leaflets through design could reduce calcification.

Biomechanical Phenomena↗
PubMedDate not supplied

Endothelial cell seeding onto the extracellular matrix of fibroblasts for the development of a small diameter polyurethane vessel.

A variety of experiments of endothelial cell seeding on artificial vessels have been performed. To improve endothelialization, one or two extracellular matrix components have been used as an underlying matrix. Although these methods have succeeded in in vitro experiments, they have not performed well in vivo. In this study, the authors used the whole extracellular matrix (ECM) excreted from fibroblasts as an underlying matrix. Fetal human fibroblasts were cultured on a polyurethane (PU) sheet. After confluence was attained, the cytoskeleton and the nuclei of the fibroblasts were destroyed using Triton-X, mitomycin, and irradiation. Omental microvascular endothelial cells from adult humans were seeded on various supports. After 12 days in culture, the cells were counted. The authors found that the ECM treated by irradiation had the highest cell number. In addition, the cells on this support exhibited the best morphologic appearance. Finally, the authors performed preliminary animal experiments. The PU vessels (inner diameter: 1.5 mm) treated with ECM were implanted in the arteries of rats. After the vessels had been implanted for 5 weeks, the authors found that the surface of the PU vessels were completely covered with endothelial cells. On the basis of these results, the authors conclude that the whole ECM makes a better underlying substrate for the endothelialization of small diameter artificial vessels.

Anastomosis, Surgical↗
PubMed1995

Use of a polyurethane carrier for assessing the survival of helminth eggs in liquid biological sludges.

Soft expanded polyurethane (plastic foam) was used as an egg carrier. A carrier of helminth eggs and a method for their isolation were tested. They proved applicable to evaluation of the survival of helminth eggs in liquid biological substrates (sludges, liquid excrements). The inside of the carrier was inoculated with 1,000 +/- 50 Ascaris suum eggs. After 21 days of incubation in an aerated medium at room temperature, 660.7 (66.1%) eggs were isolated on the average (n = 10, Tab. I). The carriers incubated in the medium at 4 degrees C yielded 716.2 eggs (71.6%) on the average (Tab. II). The intactness of the carriers in helminth eggs was proved during 21 days of incubation in aerated medium when the detected mean percentage of embryonated eggs was 80.5% (Fab. I). From the carriers kept at 4 degrees C for 21 days and subsequently incubated 76.6% of embryonated eggs were recovered on the average (Tab. II). Control showed 80.95% of embryonated eggs on the average, which is a statistically insignificant difference (P < 0.05). With the use of the carrier more than a 13-fold increase in the viable eggs was recorded, compared with a 5% yield obtained at a direct inoculation into liquid substrates. This method is rewarding for its optimization of experimental results and for reducing the number of eggs used in the experiments.

Animals↗
PubMed1996

Plasma protein adsorption to sulfonated poly(ethylene oxide)-grafted polyurethane surface.

Adsorption of proteins (fibrinogen, albumin, and gamma globulin) from plasma onto surface-modified PUs (PU-PEO, PU-SO3, and PU-PEO-SO3) was evaluated. Adsorbed fibrinogen at steady state decreased in the order PU-SO3 > PU > PU-PEO-SO3 > PU-PEO, suggesting that sulfonate groups have specific high affinity to fibrinogen. The intermediate fibrinogen adsorption on PU-PEO-SO3 can be explained by the compensatory effect between the low protein binding affinity of the PEO chain and the high fibrinogen binding affinity of the sulfonate group. In addition, PU-PEO-SO3 showed a very fast fibrinogen adsorption due to the high accessibility of the sulfonate group to fibrinogen by the poly(ethylene oxide) (PEO) spacer. The kinetic profiles of their surfaces showed that as the adsorption time increases, fibrinogen initially adsorbed was decreased and a plateau reached, demonstrating that all the surfaces exhibited the Vroman effect (the fibrinogen displacement phenomenon). PU-PEO showed the least fibrinogen and albumin adsorption among PUs, confirming the known nonadhesive property of PEO chains. It is very interesting that PU-PEO-SO3 exhibited the highest adsorption of albumin and the lowest adsorption of IgG. Therefore, it may be concluded that such adsorption behaviors of proteins to PU-PEO-SO3 contribute to improved blood compatibility.

Adsorption↗
PubMed2001

Fixation strength of swellable bone anchors in low-density polyurethane foam.

This study represents a natural extension of our previous efforts in the design and development of a new class of swellable bone anchors, which absorb body fluids and achieve fixation by an expansion-fit mechanism. Specifically, this study investigates (i) correlations between the optimal swelling strain for highest fixation strength and the foam (or bone) density, and (ii) the influence of a threaded surface on the fixation strength of the swellable implant. For this purpose, the immediate and the final (after swelling) fixation strengths of two variations of the swellable bone anchor designs (a smooth anchor and a screw anchor) were measured in two different foams (used to simulate bone) with different densities. The amount of swelling was varied systematically for each foam and anchor design combinations. This study indicates that the screw swellable anchors have higher initial fixation strength than smooth swellable anchors, but the final fixation strengths of both anchors are quite similar. Further, it is observed that the optimal swelling strain decreased with increasing foam density. Both the smooth and screw swellable anchors were also found to exhibit higher fixation strengths than the metallic screws of similar geometry.

Biocompatible Materials↗
PubMed2001

Studies on the effect of virtual crosslinking on the hydrolytic stability of novel aliphatic polyurethane ureas for blood contact applications.

The effect of virtual crosslinking on the hydrolytic stability of completely aliphatic novel poly(urethane ureas), HFL9-PU1 (hard-segment content 57.5%) and HFL13-PU2 (hard-segment content 67.9%) based on 4,4'-methylene bis(cyclohexyl isocyanate) (H(12)MDI)-hydroxy-terminated polybutadiene-1,6-hexamethylene diamine, was studied. Fourier transform infrared-attenuated total reflectance and wide-angle X-ray diffraction studies revealed hydrogen-bonding interaction and microphase separation and formation of crystallites by short- and long-range ordering in hard-segment domains. Three-dimensional networks from hydrogen bonding in the present polymers lead to virtually crosslinking and insolubility. These polymers were noncytotoxic to L929 fibroblast cells. The hemolytic potential is below the accepted limit. The studies on in vitro biostability in Ringer's solution, phosphate buffered saline, and papain enzyme revealed no weight loss. The infrared spectral studies revealed changes in the surface, especially on HFL9-PU1 aged in Ringer's solution and phosphate buffered saline, and no changes when aged in papain. The marginal changes noticed in tensile properties were attributed to the changes in degree of hydrogen bonding and associated rearrangement of molecular structure in the bulk. The results revealed that the lesser the crosslinking in virgin polymer, the higher the crosslinking in aged polymer and vice versa. Increased crosslinking during aging provided increased tensile properties in the aged polymer over the virgin polymer and vice versa. For comparison, an aliphatic polyetherurethane urea (HFL16-PU3) was also synthesized using poly(oxy tetra methylene glycol) in addition to the above reactants. Though both HFL9-PU1 and HFL16-PU3 contained the same hard-segment content, the aged sample of the latter showed decreased tensile properties with increased crosslinking during aging in contrast to the former. This was attributed to less microphase separation in the virgin HFL16-PU3 polymer.

Age Factors↗
PubMed2005

Asthma death after spraying polyurethane truck bedliner.

BACKGROUND: Isocyanate exposure is the most common cause of work-related asthma. In 2003, a male in his mid-40s died of an acute asthmatic reaction approximately 1 hr after he sprayed the inside of a cargo van with an isocyanate-containing truck bedliner. This is the first reported death attributable to this type of isocyanate application. METHODS: The Michigan Fatality Assessment and Control Evaluation (MIFACE) program investigated this work-related fatality to identify the factors that contributed to his death. The investigation included site visits, personal interviews, and a review of pertinent documents. RESULTS: Factors contributing to his death included: the vehicle type; lack of engineering controls; lack of a company safety and health program, including a personal protective equipment program, medical monitoring, and employee training; and a lack of recognition of work-relatedness of the deceased's respiratory problems by a health care provider. CONCLUSIONS: This work-related fatality investigation demonstrates the need for isocyanate manufacturers/formulators to inform end users of their products of appropriate health and safety work practices associated with new technologies. In addition, health care providers need more education and assistance to recognize and manage work-related asthma.

Adult↗
PubMed1995

Kinetics of drug delivery to the arterial wall via polyurethane-coated removable nitinol stent: comparative study of two drugs.

Polymer-coated removable stents were used to deliver 14C-labeled etretinate and 3H-labeled forskolin to the vessel wall in 31 New Zealand White rabbits to study their kinetics. Stents loaded with etretinate (n = 8) and forskolin (n = 14) were implanted in the rabbit carotid arteries, and the animals were euthanized at different time intervals. Drug levels were measured in the media and adventitia of the stented segment, in distant tissues, and in blood. In four rabbits, forskolin-loaded stents were percutaneously retrieved 2 hr after implantation in the carotid artery, and the tissue and blood levels were determined 2 and 24 hr after retrieval. In seven rabbits etretinate-loaded stents were retrieved 72 hr after implantation in abdominal aorta, and drug levels were measured in the tissues and blood immediately after and at 1 and 4 days after retrieval. Levels of etretinate in the vessel wall peaked at 24 hr (250 ng/mg) and remained high up to 72 hr (185 ng/mg) after stent placement. Levels of forskolin peaked within 2 hr of stent placement (135 ng/mg) and rapidly declined to 4.9 ng/mg at 24 hr with the stent in situ. About 50% (1.4 mg) of the original etretinate remained in the stent at 72 hr compared to about 5% (0.08 mg) of forskolin at 24 hr. Ratio of peak drug levels in the vessel wall to those in the blood was 6,000 for etretinate and 780 for forskolin. (ABSTRACT TRUNCATED AT 250 WORDS)

Alloys↗
PubMed2001

Blends of stearyl poly(ethylene oxide) coupling-polymer in chitosan as coating materials for polyurethane intravascular catheters.

To optimize the surface biocompatibility of the intravascular catheter, an amphiphilic coupling-polymer of stearyl poly (ethylene oxide) -co- 4,4'-methylene diphenyl diisocyanate-co- stearyl poly (ethylene oxide), for short MSPEO, was specially designed as the surface modifying additive (SMA). The blend of MSPEO in chitosan was coated on the outer wall of the catheters by the dip-coating method. The surface analysis was carried out by ATR-FTIR and contact angle measurements. The surface enrichment of MSPEO was confirmed. On the water interface, the larger the molecular weight of PEO was, the higher the surface enrichment. While on air interface, the case was the contrary. Three kinds of static test of clotting time, plasma recalcification time (PRT), prothrombin time (PT), and thrombin time (TT), as well as the static platelet adhesion experiment were carried out. The results indicated that the coated surface could resist the clotting effectively. In order to test the blood-compatibility of the coated catheters under a shear of blood flow, the dynamic experiment was performed through a closed-loop tubular system with the shear rate of 1500 s(-1). The results of blood regular testing at six different times (0, 5,10, 20, 30, and 60 min) indicated that the biocompatibility of the coating was nearly ideal. Finally, the SMA-MSPEO was proved to be non-chronic-toxic by animal experiments with rats and suitable as a coating material for clinical use.

Animals↗