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At least 685 records · Page 38Linked to original sources
PubMed2002

Tissue response to microfibers of different polymers: polyester, polyethylene, polylactic acid, and polyurethane.

Tissue response to single polymer microfibers of polyester (PET), polyethylene (PE), poly(L-lactic acid) (PLA), and polyurethane (PU) was assessed using a rat subcutaneous model. Fibers of diameters ranging from 1 to 15 microm were aligned parallel to each other on polycarbonate frames and implanted in the subcutaneous dorsum in the subscapular region. After 5 weeks of implantation, fibrous capsule thickness was significantly less for fibers of diameters 1-5 than for those of 11-15 microm for all polymers tested. For PET and PU, 75.0 and 71.4% respectively of the 1-5 microm fibers had no capsule, while for PE and PLA only 45.5 and 56.3% respectively had no capsule. For 1-5 microm fibers, PE had significantly thicker capsules than PET and PU. Reducing fiber diameters from 6-10 to 1-5 microm induced a greater reduction in capsule thickness than changing polymers among PET, PE, and PLA. PU showed the least encapsulation of all polymers, demonstrating significantly thinner capsules than PET, PE, and PLA for 6-10 and 11-15 microm fibers.

Animals↗
PubMed2002

Thermal property and processability of elastomeric polymer alloy composed of segmented polyurethane and phospholipid polymer.

To develop a thermoplastic elastomer with high blood compatibility, a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was blended with the segmented polyurethane (SPU) for preparing the polymer alloy. A tensile strength measurement was carried out to evaluate its mechanical strength. The mechanical strength of the SPU/MPC polymer alloy is the same as that of the original SPU and sufficient for use in medical applications. The thermal properties of the polymer alloy were evaluated by differential scanning calorimetry (DSC). The DSC curves indicated that the MPC polymer blended into the SPU did not affect the hard segment domain of the SPU. The SPU/MPC polymer alloy can be processed by heat treatment at 150 degrees C. Even after heat treatment, the SPU/MPC polymer alloy showed good mechanical properties, and MPC units were observed on the surface. Protein adsorption from human plasma was observed to evaluate the blood compatibility of the polymer alloy. The SPU/MPC polymer alloy suppressed protein adsorption on the surface before and after the heat treatment. Based on these results, it is concluded that the SPU/MPC polymer alloy has an excellent potential for application in various medical devices.

Adsorption↗
PubMed1974

Adhesion of synthetic organic polymer on soft tissue. I. A fast setting polyurethane adhesive.

Conventional polyurethane prepolymers have been shown to adhere to living biological tissues. However, their setting is not sufficiently expedient to permit convenient applications in vivo. A prepolymer prepared from the highly reactive 6-chloro-2,4,5-trifluoro-1,3-phenylene diisocyanate, castor oil, and a trace of pyridine has afforded an adhesive which sets in about 2 min in vivo. The fast setting has resulted in poor adhesion on biological tissue. The bonding has been improved by the inclusion of tolylene diisocyanate in the composition without affecting the fast curing rate of the prepolymer. The dispersion of the adhesive and its cohesion after solidification have been adjusted by other minor additives. Preliminary evaluation on animals indicates that this adhesive is most useful as a hemostatic coating in hepatic lacerations.

Animals↗
PubMed1982

A study of the interface between a fibrous polyurethane arterial prosthesis and natural tissue.

Fibrous polyurethane samples were implanted in subcutaneous tissue, muscle, and as an arterial prosthesis for periods up to six months. The interface between the polymer and living tissue was studied using optical, scanning, and transmission electron microscopy. A good correlation was found between the micromorphology of the polymer-tissue interface observed in three experimental methods used. Ingrowth of tissue occurs by cell penetration into the fibrous network of the polymer implant and eventual encapsulation by connective tissue. Full details of the distribution of collagen and the cell components around the individual polymer fibers and the structure of the connective tissue are given.

Animals↗
PubMedDate not supplied

A segmented polyurethane composite prosthetic anterior cruciate ligament in vivo study.

A segmented polyurethane prosthetic anterior cruciate ligament prototype has been developed and its in vivo integrity assessed in canine subjects. Prosthetic ligaments surgically implanted for 3, 4, 6, 8, 12, and 16 months were assessed clinically in living subjects, at time of autopsy, and microscopically postautopsy. It was found that the ligaments were adequate in strength to provide stability and last for periods up to 16 months. Notching of the ligaments was observed at two designated friction points.

Animals↗
PubMedDate not supplied

Transmission of water through a biocompatible polyurethane: application to circulatory assist devices.

The permeability characteristics of a water-segmented polyurethane (Biomer) system under the conditions encountered in circulatory-assist devices were investigated. A diffusion cell and permeability system providing precise control of membrane boundary conditions and allowing continuous measurement of water vapor transmission was designed. Liquid water at 37 degrees C was used as the donor fluid and the system incorporated a constant-flow nitrogen carrier gas and an optical dew point sensor downstream to determine the water vapor mass flow rate as a function of time. The mass flow rate was then numerically integrated and plotted against time to allow calculation of effective diffusion coefficient (D) by the dynamic time lag method. Steady-state permeabilities were found to be insensitive to donor chamber hydrostatic pressure (50-200 mm Hg) indicating that bulk flow is not a transport mechanism in these membranes. The permeability coefficient (P) was independent of membrane thickness (H) over the four samples tested (0.0102, 0.0148, 0.0269, and 0.0366 cm), with an average value of 3.29 X 10(-4) cm2/s. Thus, diffusion was Fickian with negligible boundary layers. A plot of lag time versus H2 was linear (R = 0.98) yielding a value for D of 2.18 X 10(-7) cm2/s. A water-Biomer partition coefficient was determined for each sample with an average value of 1525, indicating a moderately hydrophilic membrane with a water sorption of 6.3% at 37 degrees C. Since water transport is by Fickian diffusion in the absence of bulk flow, liquid water cannot be expected to accumulate in circulatory-assist devices unless a condensing surface is maintained within the system.

Biocompatible Materials↗
PubMed1988

Heparin immobilization onto segmented polyurethane-urea surfaces--effect of hydrophilic spacers.

Heparin was immobilized onto segmented polyurethane-urea surfaces (Biomer) using hydrophilic poly(ethylene oxide) spacers of different chain lengths. The use of the hydrophilic spacer, poly(ethylene oxide), reduces protein adsorption and subsequent platelet adhesion on the surface. In addition, the bioactivity of the immobilized heparin is enhanced by the incorporation of these spacers. Immobilized heparin bioactivity is shown to be a function of PEO spacer length. Use of hydrophilic PEO spacers demonstrates that immobilized heparin's bioactivity is consistently higher than that of the C6 alkyl spacer, but heparin-immobilized surfaces demonstrate no chain length effect on platelet adhesion, even though they show less platelet adhesion compared to Biomer controls. In the case of PEO-grafted surfaces, platelet adhesion is decreased compared to Biomer controls, and C6 alkyl spacer-grafted surfaces, and exhibits a minimum at PEO 1000. In ex vivo A-A shunt experiments under low flow and low shear conditions, all heparinized surfaces exhibit significant prolongation of occlusion times compared to Biomer controls, indicating an ability of immobilized heparin to inhibit thrombosis in whole blood.

Animals↗
PubMed1989

Preparation and surface characterization of PEO-grafted and heparin-immobilized polyurethanes.

Surfaces of commercial polyurethanes (PUs) were modified by poly(ethylene oxide) (PEO) grafting and/or heparin immobilization for long-term biomedical applications. PU surfaces were treated with diisocyanate and then reacted with PEO or heparin. The heparin immobilized by various methods on the PU surface was very stable, with concentrations of 1.45-1.84 micrograms/cm2. Surface structure and characteristics of each modified PU were examined by performing the following surface analyses: attenuated total reflection infrared (ATR-IR), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), and dynamic contact angle measurements. The reaction scheme and surface chemical structure of modified PUs were confirmed by ATR-IR and ESCA, respectively. SEM results showed that the PU-PEO surface was very smooth and that the smoothness of the heparinized PU surfaces varied, depending upon the solvent and coupling agent used in the process. The hydrophilicity of the surface was significantly increased after PEO grafting or heparin immobilization. Increase in the chain length of the grafted PEO resulted in significant increases in hydrophilicity and surface mobility.

Biocompatible Materials↗
PubMed1991

Negative cilia concept for thromboresistance: synergistic effect of PEO and sulfonate groups grafted onto polyurethanes.

In order to investigate the interaction between various sulfonated polyurethanes (PUs) and blood, a commercial PU surface was chemically modified by poly(ethylene oxide) (PEO), dodecanediol(DDO), and propane sultone to give hydrophilic, hydrophobic, and negative sulfonated surfaces, respectively. The blood compatibility of modified PUs was evaluated by an in vitro platelet adhesion test, activated partial thromboplastin time (APTT), and prothrombin time (PT) measurements as well as an ex vivo rabbit A-A shunt method. In the platelet adhesion test, the hydrophilic PEO grafted PUs showed less platelet adhesion than untreated PU and hydrophobic DDO grafted PU. Sulfonated PU-PEO exhibited a lower degree of adhesion and shape change of platelet. The APTT and PT, especially APTT, of the sulfonated PUs were extended, whereas those of PU-PEO and PU-DDO did not show any significant change compared with untreated PU. Meanwhile, in the ex vivo experiment, hydrophilic PEO grafted PUs showed longer occlusion times than untreated PU or hydrophobic DDO grafted PU. In addition, the incorporation of SO3 groups at the end of PU-DDO and PU-PEO, particularly PU-PEO-SO3, exhibited an enormous prolongation in occlusion time, indicating a synergistic effect of the hydrophilic PEO and the negative SO3 groups on thromboresistance. These occlusion times corresponded well to in vitro evaluation results: the less adhesion and shape change of platelet and the longer APTT and PT, the more extended the ex vivo occlusion time.

Animals↗
PubMed1991

Prevention of bacterial colonization on polyurethane in vitro by incorporated antibacterial agent.

The presence of implanted biomaterials increases host susceptibility to infections. Once established, biomaterial-mediated infections are resistant to treatment and persist until the device is removed. The objective of this work was to study the prevention of bacterial-biofilm formation on polymeric implant (polyurethane) by controlled release of incorporated antibacterial agents (parabens). By embedding parabens in PU by the solvent-cast method, matrices with amorphous dispersions (or solid solutions) were obtained. Release rate modulation was achieved by using different MW parabens and by a rate-limiting membrane. Preliminary in vitro antibacterial studies of both methyl and propyl paraben matrices exhibited significant inhibition of Staphylococcus epidermidis biofilm formation. Propyl paraben matrices (15 and 20% w/w drug load) decreased the number of colony-forming units on PU surface to 2 x 10(4)/mL, in comparison to 6 x 10(5) on control polymers. This significant reduction was obtained without any effect on the number of viable bacteria in the suspension culture. This type of delivery system provides regional prophylactic activity by creating a high local concentration of antibacterial agent.

Biocompatible Materials↗
PubMed1991

Formation of 4,4'-methylenedianiline in polyurethane potting materials by either gamma-ray or autoclave sterilization.

In this experiment, we found that a potential carcinogen, 4,4'-methylenedianiline (MDA), was produced from gamma-ray irradiated potting materials, medical thermosetting polyurethane (PU). gamma-Ray irradiated PUs were immersed in either methanol or in equine serum. The time course of MDA leached from the potting materials and other variables were compared. A significant relationship was noted between the amount extracted and the rigidity of the potting material. The accumulated amount of extracted MDA (a few ppm in the original sample) increased with increasing irradiation dose by a second-order equation. One sample indicated reduced MDA elution after irradiation in the early stage. MDA extraction with serum was 82-87% that with methanol. In one case, MDA leaching into serum in the early stage was higher than that into methanol. Autoclave sterilization did not promote MDA formation, thus indicating that autoclaving would be preferable.

Aniline Compounds↗
PubMed1992

Effect of soft segment chemistry on the biostability of segmented polyurethanes. II. In vitro hydrolytic degradation and lipid sorption.

A series of segmented polyurethanes (SPUs) with various polyol soft segments was prepared and their hydrolytic degradation and degradation due to lipid sorption was investigated. The hydrolytic degradation of the SPUs was investigated in a papain solution, where it was shown that the SPU based on poly(ethyleneoxide) (PEO) soft segment was susceptible to hydrolytic degradation. X-ray photoelectron spectroscopic (XPS) data suggest dissociation of the urethane linkage by enzymatic degradation. Degradation by lipid sorption was observed for the SPU based on a poly(dimethylsiloxane) (PDMS) soft segment. This is ascribed to the high solubility of lipid in the PDMS segment of the SPU.

Absorption↗
PubMed1992

Changes in fibrinogen adsorbed to segmented polyurethanes and hydroxyethylmethacrylate-ethylmethacrylate copolymers.

Fibrinogen adsorption from blood to biomaterials may regulate platelet adhesion and thrombus formation because of fibrinogen's central role in the coagulation cascade and its ability to bind specifically to the platelet membrane glycoprotein (GP) IIb-IIIa. Adsorption of fibrinogen from blood plasma to many materials exhibits a maximum with respect to plasma dilution and exposure time (the Vroman effect). In this study fibrinogen adsorption to several polymers was examined to ascertain the influence of controlled changes in surface chemistry on the Vroman effect. The materials included hydroxyethylmethacrylate-ethylmethacrylate (HEMA/EMA) copolymers, Biomer, and a series of segmented polyurethanes (PEUs), two of which contained fluorinated chain extenders. Each material exhibited maximal adsorption of fibrinogen at intermediate plasma concentrations. Little effect of soft-segment type or molecular weight was observed and no significant differences in fibrinogen adsorption to the fluorinated PEUs were seen. Changes in the strength of fibrinogen attachment to these materials with time after adsorption were also assessed. Fibrinogen adsorbed for 1 min was displaced more readily by blood plasma than that adsorbed for 1 h, regardless of the material. The more hydrophobic polymers exhibited greater retention of adsorbed fibrinogen. In addition, the fraction of fibrinogen retained by polyethylene depended on the amount of fibrinogen adsorbed to the surface, being greatest when the surface loading was the least. These studies indicate that spreading or transition of adsorbed fibrinogen molecules from a weakly to tightly bound state is a general consequence of protein adsorption to solid surfaces.

Adsorption↗
PubMed1995

Surface characteristics and properties of lumbrokinase-immobilized polyurethane.

Potent and novel fibrinolytic enzymes (lumbrokinase [LK]) were extracted from the earthworm, Lumbricus rubellus. These enzymes were very stable and showed greater antithrombotic activity than other currently used fibrinolytic proteins. An LK fraction showing the most potent fibrinolytic activity was immobilized onto a polyurethane (PU) surface to investigate its enzymatic activity and antithrombotic activity. A methanol-extracted PU surface was coated with 3% (wt/vol) maleic anhydride methylvinyl ether copolymer (MAMEC)/tetrahydrofuran (THF) solution, and the surface was incubated in an LK solution/phosphate-buffered saline (PBS, pH 7.4). The surface properties were characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and dynamic contact angle. The stability of immobilized LK was determined by caseinolytic activity assay and the specificity of immobilized LK on fibrinogen/fibrin was observed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The antithrombotic activity of immobilized LK was evaluated using an ex vivo rabbit A-A shunt experiment. LK immobilization was confirmed by ATR-FTIR and ESCA. Immobilized LK demonstrated stable proteolytic activity during various incubation periods. Immobilized LK proteolyzed fibrinogen and fibrin almost specifically, while it hardly hydrolyzed other plasma proteins including plasminogen and albumin. In the ex vivo A-A shunt experiment, the LK-immobilized surface significantly prolonged occlusion time over control surfaces. This is primarily due to the high thrombolytic activity of immobilized LK. In this work, a highly efficient surface modification method on the PU surface was developed, and this LK immobilization technique will be very useful in improving the blood compatibility of blood-contacting devices.

Animals↗
PubMed2003

In vivo biocompatibility of three different chemical compositions of Ricinus communis polyurethane.

Alteration in the chemical composition of a biomaterial may be undertaken to improve its biological properties. The aim of this work was to evaluate the biocompatibility of three chemical compositions of Ricinus communis polyurethane (RCP): RCPp (pure RCP), RCP + CaCO(3), and RCP +Ca(3)(PO(4))(2). RCP cylinders were surgically implanted in rabbit femurs. After 8, 12, and 16 weeks, the femurs were removed, fixed, sectioned, ground, and stained by Stevenel's blue/Alizarin red S for light microscopy and histomorphometry. The osseointegration and osseoconductivity were calculated by means of image analysis and the data were submitted to the Kruskal-Wallis test followed by Dunn's test. Osseointegration was already completed after 8 weeks on RCP + Ca(3)(PO(4))(2) because similar values were found from week 8 to 16, whereas it showed a time-dependent increase on RCPp and RCP +CaCO(3). The osseointegration was greater on RCP + Ca(3)(PO(4))(2) in all periods when compared with RCPp, and after 8 and 12 weeks when compared with RCP + CaCO(3). None of the RCP samples presented osseoconductivity. The present results showed that RCP blended with calcium phosphate improved the biocompatibility by both enhancing and accelerating its osseointegration. Based on the absence of osseoconductivity, RCP was considered to be a bioinert material.

Animals↗
PubMed2003

Low permeability biomedical polyurethane nanocomposites.

In this article we describe our continuing research on a novel nanocomposite approach for reducing gas permeability through biomedical polyurethane membranes. Nanocomposites were prepared using commercially available poly(urethane urea)s (PUU) and two organically modified layered silicates (OLS). Wide-angle X-ray diffraction experiments showed that the silicate layer spacing in the nanocomposites increased significantly compared with the neat OLS, signifying the formation of intercalated PUU/OLS structures. The nanocomposite materials exhibit increased modulus with increasing OLS content, while maintaining polymer strength and ductility. Water vapor permeability was reduced by about fivefold at the highest OLS contents, as a result of PUU/inorganic composite formation.

Calorimetry, Differential Scanning↗
PubMed2003

Effect of the chemical composition of Ricinus communis polyurethane on rat bone marrow cell attachment, proliferation, and differentiation.

Alterations in the chemical composition of a polymer may be undertaken to improve its biological properties. The aim of this study was to investigate the in vitro biocompatibility of Ricinus communis polyurethane (RCP) with three different chemical compositions: RCPp (pure RCP), RCP+CaCO(3), and RCP+Ca(3)(PO(4))(2). Rat bone marrow cells were cultivated under conditions that allowed osteoblastic differentiation and were evaluated for cell attachment, cell proliferation, cell morphology, total protein content, alkaline phosphatase (ALP) activity, and bonelike nodule formation. For the evaluation of attachment, cells were cultured for 4 h. After 3 days, cell morphology was evaluated. Cell proliferation was evaluated after 7 and 14 days. Total protein content and ALP activity were evaluated after 14 days. For bonelike nodule formation, cells were cultured for 21 days. Data were compared with an analysis of variance and Duncan's multiple range test when appropriate. Cell attachment and ALP activity were not affected by RCP chemical composition. Proliferation, total protein content, and bonelike nodule formation were all affected by RCP chemical composition. These results suggest that initial cell events are not affected by RCP chemical composition, whereas RCPs blended with calcium carbonate or, better yet, calcium phosphate, by favoring events that promote matrix mineralization, are more biocompatible materials.

Animals↗