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At least 1,207 records · Page 67Linked to original sources
PubMed2001

Studies on polyurethane potting compound based on HDI-TMP adduct for fabrication of haemodialyzer.

Polyurethane potting compounds based on hexamethylene diisocyanate-trimethylol propane (HDI-TMP) adduct (Component "A") and polypropylene glycol, polyethylene glycol and castor oil (Component "B") were prepared as potential compounds for the fabrication of haemodialyzer. The setting characteristics of the potting compounds having isocyanate index 2.0 are better than those compounds having 1.35. The aging stability of PEG and PPG based potting compounds are poorer than those of castor oil based potting compounds. Appreciable hydrolytic, oxidative and chemical stability could be observed with castor oil based potting compounds of HDI-TMP adduct.

Journal Article↗
PubMed2001

Surface modification of polyurethane for promotion of cell adhesion and growth 1: surface photo-grafting with N,N-dimethylaminoethyl methacrylate and cytocompatibility of the modified surface.

Functional polyurethane (PU) surface was prepared by photo-grafting N,N-dimethylaminoethyl methacrylate (DMAEM) onto the membrane surface. Grafting copolymerization was conducted by the combined use of the photo-oxidation and irradiation grafting. PU membrane was photo-oxidized to introduce the hydroperoxide groups onto the surface, then the membrane previously immersed in monomer solution was irradiated by UV light. The X-ray photoelectron spectroscopy and water contact angle characterized the grafted copolymers and verified the occurrence of graft copolymerization. The results showed that UV irradiation could realize the graft copolymerization effectively. The grafted membrane showed minimal surface morphology. Human umbilical vein endothelium (HUVE) cells were seeded on the grafted surfaces. The performance of the surface in cell attachment correlated with the content of oxygen and nitrogen. Cells were spread more extensive and grown faster on the surface with lower degree of grafting.

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PubMedDate not supplied

Silk fibroin-polyurethane scaffolds for tissue engineering.

Silk fibroin (SF) is a highly promising protein for its surface and structural properties, associated with a good bio- and hemo-compatibility. However, its mechanical properties and architecture cannot be easily tailored to meet the requirements of specific applications. In this work, SF was used to modify the surface properties of polyurethanes (PUs), thus obtaining 2D and 3D scaffolds for tissue regeneration. PUs were chosen for their well known advantageous properties and versatility; they can be obtained either as 2D (films) or 3D (foams) substrates. Films of a medical-grade poly-carbonate-urethane were prepared by solvent casting; PU foams were purposely designed and prepared with a morphology (porosity and cell size) adequate for cell growth. PU substrates were coated with fibroin by a dipping technique. To stabilize the coating layer, a conformational change of the protein from the alpha-form (water soluble) to the beta-form (not water soluble) was induced. Novel methodology in UV spectroscopy were developed for quantitatively analyzing the SF-concentration in dilute solutions. Pure fibroin was used as standard, as an alternative to the commonly used albumin, allowing real concentration values to be obtained. SF-coatings showed good stability in physiological-like conditions. A treatment with methanol further stabilized the coating. Preliminary results with human fibroblasts indicated that SF coating promote cell adhesion and growth, suggesting that SF-modified PUs appear to be suitable scaffolds for tissue engineering applications.

Journal Article↗
PubMed2002

Effects of thermal annealing of segmented-polyurethane on surface properties, structure and antithrombogenicity.

Analyses of the surface structure and properties of thermally heat-treated and non-treated segmented-polyurethane (SPU) surfaces showed that a crystalline structure, the domain size of which was larger than that of the micro-phase separation structure, appeared when the SPU surface was annealed in the temperature range of 60-140 degrees C. The appearance of the crystalline structure resulted in a decrease in surface free energy, that is, an increase in the hydrophobicity of the surface. Whole blood or platelet-rich plasma (PRP), when in contact with a SPU surface, which had previously been in contact with a glass surface during casting, coagulation of the whole blood occurred within approximately 30 min and, in case of PRP, in approximately 60 min. When the SPU surface was modified by thermal annealing, the coagulation time for PRP was delayed, whereas that of whole blood remained essentially unchanged. Relationships between the surface properties and the structure of annealed SPU and antithrombogenicity are discussed. The data collected herein suggest that the heat treatment of SPU might be useful for improving antithrombogenicity.

Journal Article↗
PubMed1997

A new composite made of polyurethane and glass ceramic in a loaded implant model: a biomechanical and histological analysis.

The biocompatibility and osseous integration of a new composite material made of polyurethane and a calcium silicophosphate ceramic was investigated in a loaded implant model in sheep and compared to that of commercially pure titanium. Six months after implantation, interfacial shear strength was higher between the titanium and bone than between the composite and bone. After 2 years, however, the shear strength was significantly higher in the composite group. Histologically, both implants were surrounded by bone and fibrous tissue and there were no signs of inflammation. Direct contact of bone on the composite surface increased significantly with time, whereas there was no time-dependent increase of bone contact on titanium. It can be concluded that the biocompatibility and osseous integration of the composite was very good in the loaded implant model used. It is therefore suggested that the new composite is a promising biomaterial for orthopaedic implants.

Journal Article↗
PubMed1997

Sequential polyurethane-poly(methylmethacrylate) interpenetrating polymer networks as ureteral biomaterials: mechanical properties and comparative resistance to urinary encrustation.

The mechanical properties and resistance to urinary encrustation of sequential-interpenetrating polymer networks (IPNs) composed of polyurethane (PU) and polymethylmethacrylate (PMMA), have been described. Mechanical properties were determined using tensile testing and dynamic mechanical analysis, whereas resistance to encrustation was examined using an in vitro model for encrustation simulating in vivo encrustation. Maximum and minimum tensile strength at break, Young's modulus, storage and loss moduli were associated with PMMA and PU, respectively. IPNs demonstrated intermediate mechanical properties which were dependent on the concentrations of the component polymers. Conversely, maximum elongation at break was observed for PU and this parameter decreased as the concentration of PMMA increased in the IPN. The dynamic mechanical damping parameter, tan delta, was similar for all IPNs at 37 degrees C. Increased advancing and decreased receding contact angles were observed for IPNs in comparison with the native PU. The rate and extent of encrustation, measured as the percentage surface coverage, was similar for PU, IPNs and PMMA. In contrast, encrustation on polyhydroxyethylmethacrylate, a model hydrogel, was greater than observed for the IPNs or component polymers. No apparent correlation was observed between the rate and/or extent of encrustation and polymer contact angle. It is concluded that these IPNs may be of clinical benefit in patients providing stent resistance to extrinsic compression of the ureter in comparison with native PU. The comparable resistance to encrustation between the IPNs and PU indicates that the use of IPNs should not be restricted in this regard.

Journal Article↗
PubMed1997

Endothelial cells on plasma-treated segmented-polyurethane: adhesion strength, antithrombogenicity and cultivation in tubes.

When the surface of segmented-polyurethane (SPU), where endothelial cells are not capable of proliferating, is modified by plasma treatment, the adhesion and proliferation of bovine aortic endothelial cells (BAECs) can be drastically improved. The cells were capable of proliferating on the inner surface of a plasma-treated SPU-coated tube (length: 50 mm; inner diameter: 1.5 mm). When a steady flow shear stress of 9 Pa was applied to the cells proliferated on the modified SPU surface for 90 min, most cells did not detach from the surface. From an in vitro evaluation test of antithrombogenicity, the cell surface can be considered to provide an inert surface against thrombus formation and blood coagulation. From analyses of the plasma-treated SPU surface, it was suggested that the improvements in BAEC proliferation and adhesion after plasma treatment were due to the change in wettability of the surface. Data suggest that the plasma treatment would be useful for developing a small-calibre hybrid vascular graft.

Journal Article↗
PubMed2003

Design, synthesis and properties of polyurethane hydrogels for tissue engineering.

Due to their similarity to natural soft tissues, water-swellable polymeric materials (hydrogels) are, in principle, ideal candidates for scaffolds/matrices in tissue engineering. Polyurethanes (PU), hydrophilic but water-insoluble, can be obtained by the incorporation of hydrophilic soft segments, e.g. poly(ethylene oxide) (PEO). These materials possess the favorable characteristics of the family of PUs as well as the ability to mimic soft tissues. In this work, new crosslinked PU-hydrogels were prepared in a one-step bulk polymerization process using an aliphatic diisocyanate, PEO, a low molecular weight diol, and a tri-functional crosslinking agent. A porous structure was also obtained by air-incorporation under mechanical stirring at a controlled high speed during the polymerization. Structural characteristics of the compact (PU-HyC) and the porous (PU-HyP) material were investigated. Molecular weight between cross-links, M(c), and crosslinking density, rho(x), were typical of a low crosslinking degree. A homogeneous distribution of non-interconnecting pores (phi100 microm) was observed in PU-HyP. Both materials showed a high water adsorption. The swelling behavior and weight loss in water was affected by porosity. For their mechanical behavior in the swollen state, the novel PU hydrogels can be considered for biomedical applications where good mechanical properties are required (i.e. 3D scaffold for tissue engineering).

Journal Article↗
PubMed1985

A study of calcergy in the rat induced by the implantation of polyurethane sponges soaked in lead acetate.

Polyurethane sponges were soaked in a 5 mg/ml solution of lead acetate, dried, and implanted subcutaneously in rats. Sponges soaked in distilled water were implanted as controls. The reaction to the sponges was studied from 5 h to 140 days after implantation, utilising sponge dry weight gain, rate of ingrowth of granulation tissue, histology and electron microscopy. Five hours after implantation, test sponges showed lead phosphate deposits in the central sponge zone and by one day the deposits stained positively for calcium. Transmission electron microscopy (TEM) showed needle-shaped crystals of hydroxyapatite. Ingrowth of granulation tissue into test sponges was delayed. Breakdown of the sponge matrix was observed in control sponges after 140 days. This model highlighted the physicochemical nature of the calcergic reaction, implicating fluid transudates/exudates in the initial stages.

Animals↗
PubMed1998

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler.

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.

Air Pollutants↗
PubMed1988

Implantation of 20 cm long polyurethane vascular prostheses in the femoral artery of dogs. Preliminary results.

In a preliminary experiment externally reinforced polyurethane prostheses measuring 20 cm in length, with an inner diameter of 3 mm, were implanted in a loop in the femoral artery of six dogs. The dogs received 250 mg acetylsalicylic acid and 25 mg dipyridamol three times a day as anti-thrombocyte aggregation therapy starting three weeks prior to surgery. Anti-thrombocyte aggregation therapy was continued throughout the study. All prostheses remained patent 8, 9, 15 and 17 months after implantation. Patency was confirmed by palpation and Doppler ultrasound measurements. Preliminary results suggest that in clinically relevant situations, these prostheses could function well over prolonged periods of time.

Animals↗
PubMed1990

Surgical correction of breast deformities following long-lasting complications of polyurethane-covered implants.

Breast deformities following long-lasting complications associated with the use of polyurethane prostheses are encountered with increasing frequency in our practice. Patients with this problem often feel frustrated after a long period of unsuccessful treatment and multiple operations. The anatomopathological bases of the deformity in such patients can be summarized as follows: volumetric mammary defect, soft tissue deficiency, and distortion and fibrosis of residual breast tissues. The reconstructive procedure should provide adequate aesthetic results with permanent or long-lasting symmetry, possibly in a single operative stage. The procedures employed in 12 patients are reviewed, and 3 representative cases are described in detail. The best aesthetic results in difficult cases have been achieved with either a latissimus dorsi muscular flap raised through minimal posterior incisions and transposed anteriorly to cover a permanent, expandable implant, or a suitably tailored, partly deepithelialized transverse rectus abdominis musculocutaneous flap.

Adult↗
PubMed1996

Candida albicans infection of bilateral polyurethane-coated silicone gel breast implants.

We present a report of bilateral Candida albicans infection of polyurethane-coated silicone gel prostheses and an acute onset of unilateral capsular contracture 4 years after breast augmentation. The patient was treated by removal of implants, antibiotic irrigation of the capsule cavities, and immediate replacement with new implants. Following histopathologic diagnosis, the patient was treated with a course of fluconazole and remains symptom free at the 12-month follow-up.

Adult↗
PubMed1986

"Saline float" positioning of the polyurethane-covered breast prosthesis.

The use of the "saline float" technique has enabled us to more easily position the foam-covered breast implants through a short aesthetic incision. Of 34 patients in whom this has been used, one breast has been complicated by wrinkling of the prosthesis noted early after surgery. At 6 months this is no longer evident. Retained saline has caused no problems, and no infections have been encountered. This technique offers a safe and simple solution to overcome the tissue friction associated with use of the polyurethane foam-covered prosthesis.

Breast↗
PubMed1997

Synchrotron radiation study of the relation between structure and strain in polyurethane elastomers.

This paper describes a system for the study of the relation between structure and applied strain in thermoplastic polyurethane elastomers using the Australian National Beamline Facility at the Photon Factory, KEK, Tsukuba, Japan. The system uses the sagittal focusing monochromator at beamline 20B to provide a high-intensity focused beam which then falls on the specimen mounted in a miniature tensometer mounted in the unique vacuum diffractometer (BIGDIFF). Imaging plates were used to record simultaneously SAXS and WAXS patterns from the specimen at a particular strain. The change in SAXS and WAXS patterns with loading and unloading was recorded using a ten-plate imaging-plate changer.

Journal Article↗
PubMed2002

Acoustic and dynamic mechanical properties of a polyurethane rubber.

Acoustical and dynamic mechanical measurements were carried out on a commercial polyurethane rubber, DeSoto PR1547. The sound speed and attenuation were measured over the range from 12.5 to 75 kHz and 3.9 to 33.6 degrees C. Shear modulus was measured from 10(-4) to 2 Hz and -36 to 34 degrees C. The peak heights of the shear loss tangent varied with temperature, demonstrating thermorheological complexity. At higher temperatures, time-temperature superpositioning could be applied, with the shift factors following the Williams-Landel-Ferry equation. From the combined acoustical and mechanical measurements, values for the dynamic bulk modulus were determined. Moreover, superposition of the bulk modulus data was achieved using the shift factors determined from the dynamic mechanical shear measurements. Finally, this work illustrates the capability and the working rules of acoustical measurements in a small tank.

Journal Article↗
PubMed1989

Efficacy of dicloxacillin-coated polyurethane catheters in preventing subcutaneous Staphylococcus aureus infection in mice.

In a mouse model, dicloxacillin-coated polyurethane catheters or control (uncoated) catheters were placed subcutaneously and then Staphylococcus aureus was inoculated at the time of insertion, 24 or 48 h later. The in vivo half-life of the antibiotic was 11 to 16 h. When 10(5) CFU of S. aureus were inoculated at the time of catheter insertion, dicloxacillin-coated catheters kept the number of S. aureus removed from catheters by sonication below 10(2) CFU at 12, 24, 48, and 96 h after inoculation compared with titers greater than 10(3.5) CFU for control catheters (P less than 0.05). When S. aureus was inoculated 24 h after catheter insertion, control catheters averaged greater than 10(2) CFU of S. aureus removed compared with less than 10(1.5) CFU for the dicloxacillin-coated catheters (P less than 0.05). No difference was found between coated and control catheters when S. aureus was inoculated 48 h after catheter insertion, but S. aureus titers averaged less than 10(2) CFU for all experimental groups. Our data suggest that in mice, regional prophylaxis of S. aureus subcutaneous space infection is feasible with catheters coated with dicloxacillin and that the presence of antibiotic is only necessary for the first 24 to 48 h.

Animals↗