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At least 523 records · Page 29Linked to original sources

PubMed2006

Clinical field testing of polyurethane feet for trans-tibial amputees in tropical low-income countries.

In a prospective controlled study, 172 polyurethane feet of different designs were fitted to 155 amputees with trans-tibial prostheses. These were followed in respect of their durability. The amputee compliance was in general good, and 87% were satisfied with their device. After 18 months the failure rate of 20% with the CIREC spring-blade foot was significantly better than the others, but poorer craftsmanship, higher complaint rate and lower compliance rate cast some doubt on the results. The results with the conventional SACH foot constructions with polyurethane as filling and covering materials were so poor after 18 months that their use cannot be recommended in tropical areas of the developing world.

Adolescent↗

PubMed2000

The determination of the ability of polyurethane foam to release toluene diisocyanate into air.

A study was conducted to assess the ability of polyurethane foam to release toluene diisocyanate (TDI) into the air. The study was completed in two phases. In the first phase, three-day post-production foam samples were "extracted" using 37 degrees C, 30 percent relative humidity air for a total of three days. In the second phase, foam samples were "loaded" with TDI (approximately 1 ppm (w/w) in the foam) by passing air containing a controlled level of TDI vapor through the foam. The "loaded" foam was then aged for three days (to simulate minimum possible expected time between production and consumer contact) before being extracted for three days using 37 degrees C, 30 percent relative humidity air. In both phases of the study, the extracted TDI was quantified by trapping it from the air using glass-fiber filters coated with 1,(2-pyridyl)piperazine (PP) derivatizing agent (modified OSHA Method 42) then analyzing the TDI derivative formed using high-performance liquid chromatography with ultraviolet detection. Validation of the test system was conducted using diffusion-tube-generated TDI atmospheres. Results of the Phase 1 portion of the study showed no quantifiable TDI being extracted from the three-day post-production commercial foam samples at a limit of quantitation of approximately 0.1 ppb TDI in air. Results of the Phase 2 portion of the study showed no quantifiable TDI being extracted from the "loaded" foams at a limit of quantitation of 0.12 microgram TDI (less than 0.03% of the level of TDI loaded into the foams). In conclusion, the results from this study indicate that it is not likely that TDI would be released from three-day post-production polyurethane foams in amounts likely to produce air concentrations of concern.

Air Pollutants, Occupational↗

PubMed2003

A life-cycle comparison of several auxiliary blowing agents used for the manufacture of rigid polyurethane foam.

In a commitment to zero ozone depletion, the United Nations and the U.S. Environmental Protection Agency (EPA) have called for the phase-out of the manufacture and import of hydrochlorofluorocarbons (HCFCs), used as auxiliary blowing agents (ABAs) in the manufacture of polyurethane foams. As a result, more environmentally benign alternative ABAs are being sought by the foam-blowing industry. This study examined the life cycle of HCFC-22, hydrofluorocarbon-134a (HFC-134a), and cyclopentane, which are currently used or considered as potential alternative ABAs in the manufacture of rigid polyurethane foams that serve as insulation in a model North American refrigerator. The raw material extraction/refining, manufacturing, use, and disposal stages of the life cycle of each ABA were considered, and their resulting relative impacts on ozone depletion and global warming were compared. The manufacturing, use, and disposal stages were determined to affect ozone depletion and global warming to the largest extent, emphasizing the need for a greater focus on pollution prevention opportunities in these stages. The HFC-134a life cycle yields no impact on ozone depletion and a significantly decreased global warming impact compared with its predecessor, HCFC-22, and a tradeoff of slightly higher global warming impact and fewer added safety concerns compared with its more flammable counterpart, cyclopentane.

Construction Materials↗

PubMed1997

Workers exposed to thermal degradation products of TDI- and MDI-based polyurethane: biomonitoring of 2,4-TDA, 2,6-TDA, and 4,4'-MDA in hydrolyzed urine and plasma.

The aim of the study was to investigate biomarkers of exposure to thermal degradation products of 2,4- and 2,6-toluene diisocyanate (TDI)- and 4,4'-methylenediphenyl diisocyanate (MDI)-based polyurethane and the toxicokinetics of these products. Blood and urine were collected from 15 factory workers exposed to thermal degradation products of MDI-based polyurethane glue and TDI-based flexible foam. Four of these workers were also studied during an exposure-free period. Urine and plasma were analyzed after acidic hydrolysis and the concentrations of the isocyanates' corresponding amines, 2,4-, 2,6-toluenediamine (TDA), and 4,4'-methylenedianiline (MDA), were determined as derivatives of pentafluoropropionic anhydride by gas chromatography using chemical ionization mass spectrometry monitoring negative ions. Urinary elimination rates were in the range of < 0.01-5.7 micrograms of 2,4-TDA per hour, < 0.01-3.5 micrograms of 2,6-TDA per hour, and < 0.01-1.6 micrograms of 4,4'-MDA per hour. Plasma levels were in the range of < 0.1-5.5 ng of 2,4-TDA per mL, < 0.1-2.3 ng of 2,6-TDA per mL, and < 0.1-45 ng of 4,4'-MDA per mL. The urinary half-lives of 4,4'-MDA for four of the workers were found to be 59, 61, 73, and 82 hours. The half-lives of 4,4'-MDA in plasma were 10, 14, 16, and 22 days. Elimination rate peaks of 2,4-TDA, 2,6-TDA, and 4,4'-MDA in urine varied during and between workdays. The individual variation in plasma concentrations of 2,4-TDA, 2,6-TDA, and 4,4'-MDA with time was small, but between individuals the variation was great.

Air Pollutants↗

PubMed1989

Evaluation of the elastic behaviour of central venous PVC, polyurethane and silicone catheters.

Eighty used and 20 new silicone, polyurethane and polyvinylchloride central venous catheters were tested to establish the Young's modulus and the bending stiffness of the catheters and their introducers. The catheters were subjected to longitudinal traction forces and their lengthening measured. Young's modulus and the geometric moment of inertia were then calculated. It is shown that polyurethane catheters show least variation in their elastic characteristics, and that silicone catheters offer least resistance to bending and do not change their elastic properties after use. All catheters were equally unlikely to cause thrombus production if this is related to excessive bending stiffness.

Catheterization↗

PubMedDate not supplied

Assessment of tissue ingrowth rates in polyurethane scaffolds for tissue engineering.

The continuous development of new biomaterials for tissue engineering and the enhancement of tissue ingrowth into existing scaffolds, using growth factors, create the necessity for developing adequate tools to assess tissue ingrowth rates into porous biomaterials. Current histomorphometric techniques evaluating rates of tissue ingrowth tend either to measure the overall tissue content in an entire sample or to depend on the user to indicate a front of tissue ingrowth. Neither method is particularly suitable for the assessment of tissue ingrowth rates, as these methods either lack the sensitivity required or are problematic when there is a tissue ingrowth gradient rather than an obvious tissue ingrowth front. This study describes a histomorphometric method that requires little observer input, is sensitive, and renders detailed information for the assessment of tissue ingrowth rates into porous biomaterials. This is achieved by examining a number of computer-defined concentric zones, which are based on the distance of a pixel from the scaffold edge. Each zone is automatically analyzed for tissue content, eliminating the need for user definition of a tissue ingrowth front and thus reducing errors and observer dependence. Tissue ingrowth rates in two biodegradable polyurethane scaffolds (Estane and polycaprolactone-polyurethane [PCLPU]) specifically designed for tissue engineering of the knee meniscus were assessed. Samples were subcutaneously implanted in rats with follow-up until 6 months. Especially at the earlier follow-up points, PCLPU scaffolds showed significantly higher tissue ingrowth rates than Estane scaffolds, making the PCLPU scaffold a promising candidate for further studies investigating meniscus tissue engineering.

Animals↗

PubMed2006

Effects of electromagnetic stimulation on calcified matrix production by SAOS-2 cells over a polyurethane porous scaffold.

There is increasing interest in designing new biomaterials that could potentially be used in the form of scaffolds as bone substitutes. In this study we used a hydrophobic crosslinked polyurethane in a typical tissue-engineering approach, that is, the seeding and in vitro culturing of cells using a porous scaffold. Using an electromagnetic bioreactor (magnetic field intensity, 2 mT; frequency, 75 Hz), we investigated the effect of the electromagnetic stimulation on SAOS-2 human osteoblast proliferation and calcified matrix production. Cell proliferation was twice as high; expression of decorin, osteocalcin, osteopontin, type I collagen, and type III collagen was greater (1.3, 12.2, 12.1, 10.0, and 10.5 times as great, respectively); and calcium deposition was 5 times as great as under static conditions without electromagnetic stimulation. RT-PCR analysis revealed the electromagnetically upregulated transcription specific for decorin, fibronectin, osteocalcin, osteopontin, transforming growth factor-beta, type I collagen, and type III collagen. The immunolocalization of the extracellular matrix constituents showed their colocalization in the cell-rich areas. The bioreactor and the polyurethane foam were designed to obtain cell colonization and calcified matrix deposition. This cultured biomaterial could be used, in clinical applications, as an osteoinductive implant for bone repair.

Bioreactors↗

PubMed2003

Clinical and Doppler ultrasonography data of a polyurethane vascular access graft for haemodialysis: a prospective study.

BACKGROUND: Absence of a permanent vascular access in most patients starting haemodialysis remains a cause of high morbidity and costs. This study obtained new clinical and colour Doppler ultrasound (CDU) data of a polyurethane vascular access graft (PVAG) proposing early post-operative cannulation. METHODS: Baseline characteristics were determined in 15 patients and the PVAGs were evaluated prospectively including first cannulation, patency and complications. CDU was used post-operatively and after 1 year for assessing graft morphology and access blood flow. RESULTS: PVAGs were cannulated at a median of 4 days post-operatively. The 1-year primary patency of the PVAG was 66.7%. During the 15 months observation three grafts thrombosed, one was replaced because of infection and one because of ischaemia. CDU measurements at the feeding brachial artery revealed a mean initial access volume flow of 773+/-89 ml/min, being significantly higher in patients without thrombosis compared to patients with thrombotic events (930+/-90 vs 375+/-143 ml/min, P<0.05). The initial inability to directly monitor PVAGs by CDU changed at sites of frequent centesis, where Doppler signals and luminal morphology could be evaluated in the follow up examination. CONCLUSIONS: The PVAG offers early access for urgent haemodialysis. CDU for access volume flow measurement at the feeding brachial artery contributes to predict access thrombosis. Direct non-invasive graft imaging is limited and the ultrasonographical changes in the polyurethane material enabling graft monitoring after repeated cannulation might indicate an injury of the graft with increased risk for access failure.

Adult↗

PubMed1996

Palliative therapy using polyurethane-covered self-expandable metallic stents for malignant esophageal strictures: experiences in six patients.

To evaluate the utility and limitations of palliative stenting with polyurethane-covered self-expandable metallic stents, 6 patients (3 males and 3 females ranging in age from 58-85 [mean 72.1] years) with malignant esophageal strictures were treated with these stents between April 1993 and October 1995. Three had esophageal carcinoma, two had gastric carcinoma and one had lung carcinoma. Song-type self-expandable metallic stents were inserted by intubation under local laryngeal anesthesia. A retriever was attached in 4 stents and an anti-reflux mechanism was attached in 2 stents placed over the esophagocardiac strictures. The stents were placed successfully in all patients, and no major complication related to intubation was encountered. All the stents fully expanded within 3 days after insertion. The grade of dysphagia was improved in 5 (83%) of the 6 patients. One stent was extracted using a retriever in one patient with no improvement. No reflux symptoms were observed in 2 patients whom received stents with an anti-reflux mechanism. No blockage of the stent due to food impaction or secondary stricture occurred in any patient during the observation period. One stent migrated into the stomach in one patient 27 days after insertion. Esophageal stenting with polyurethane-covered self-expandable metallic stents is a relatively safe and effective palliation for malignant esophageal strictures.

Aged↗

PubMed1991

Nineteen years' experience with polyurethane foam-covered mammary prosthesis: a preliminary report.

Long-term reviews of patients undergoing augmentation mammaplasty seem to be rare. Recently, a long-term study of patients who had undergone augmentation with polyurethane foam-covered prostheses was undertaken. However, at the time that study was published, the longest follow-up was just over 4 years. We have been using the polyurethane-coated prosthesis almost exclusively for nearly 20 years. The procedure is performed by one surgeon using a consistent technique, and all implantations were retroglandular. In reviewing this series, a follow-up rate of nearly 60% was achieved in patients augmented for periods of 1 to 19 years. The length of this study, together with a high follow-up compliance rate, makes this an unusual contribution to the literature on augmentation mammaplasty.

Biocompatible Materials↗

PubMedDate not supplied

Kinetics and quantitation of In-111 labeled platelet deposition on control and heparin-bonded polyurethane angio catheters in a dog model.

The dynamics of platelet deposition on control polyurethane catheters (CPC) and heparin-bonded polyurethane catheters (HBPC) were evaluated with In-111 labeled platelets (In-PLT) using a computerized gamma camera (CGC). Ten nonheparinized dogs (18-25 kg) had both femoral arteries catherized with 10 cm of CPC and HBPC (5 Fr.) 24 hr postinjection of 300-420 microcuries of In-PLT, and imaged for 3 hr with a gamma camera. Regional platelet deposition on three segments of catheters and the puncture site was determined. Catheters were harvested and radioactivity on the catheter segments (proximal: PROX, middle: MID, distal: DIST and puncture site: PS) of both was determined. From the platelet count in blood, and radioactivity in blood and segments of catheters, adjacent artery, and area of artery and catheter, the platelet-density [X10(3) (mean +/- S.D.)] on catheter and artery was calculated and tabulated. Proximal values were cath (CPC), 1289 +/- 1125; artery, 1355 +/- 587; cath (HBPC), 125 +/- 113; artery, 1149 +/- 1620. The middle values were cath (CPC), 1102 +/- 1109; artery, 1512 +/- 625; cath (HBPC), 132 +/- 108; artery, 1011 +/- 942. Distal values were cath (CPC), 780 +/- 584; artery, 132 +/- 108; cath (HBPC), 227 +/- 194; artery, 1457 +/- 1309. The puncture site values were cath (CPC), 106 +/- 382; artery, 1011 +/- 942; cath (HBPC), 164 +/- 135; artery, 1498 +/- 1240. The large standard deviation in retained platelets is due to embolization. The platelet-density and regional counts on catheter segments were lower with HBPC than CPC, as was the rate of platelet-deposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography↗

PubMedDate not supplied

Effects of radiofrequency glow discharge and oligopeptides on the attachment of human endothelial cells to polyurethane.

Activation of the surface of small diameter polyurethane vascular grafts using radiofrequency glow discharge (RFGD) and covalent linkage of cell attachment oligopeptides may improve graft patency. The effects of RFGD treatment were investigated on a polyurethane-polydimethylsiloxane (PU-PDMS) copolymer (Cardiothane-51; Kontron Cardiovascular, Inc., Everett, MA) membrane fabricated using the spray, phase-inversion technique. RFGD using H2O vapor was used to functionalize the membrane surface, reacted with 1',1 carbonyldiimidazole and covalently bound with oligopeptides (RGDS, RGES). Membranes not subjected to RFGD, either unmodified or with adsorbed fibronectin (Fn), vitro-nectin (Vn), RGDS, RGDV, and RGES, were used as controls. RFGD treated membrane surfaces were evaluated using electron spectroscopy for chemical analysis, which demonstrated a qualitative increase in nitrogen and silicon compared to unmodified PU-PDMS. Indirect confirmation of surface hydroxylation was provided by metallization with palladium and nickel, demonstrating uniform metallization of RFGD treated PU-PDMS surfaces. Human umbilical vein endothelial cells (HUVEC) were seeded at a density of 10(4) cells/cm2 and cell attachment assessed at 3 hr, 24 hr, and 7 days. Untreated PU-PDMS and membrane with adsorbed oligopeptides demonstrated poor HUVEC attachment at all intervals. Adsorbed Fn and Vn had significantly better early cell attachment and growth (p < 0.01). RFGD improved initial attachment and growth over non-RFGD treated controls (p < 0.01) for RGDS bound membranes, which performed as well as Fn controls (N.S.). PU-PDMS membranes can be modified using RFGD to covalently link oligopeptides. RFGD treatment alone, or with covalent linkage of cell attachment oligopeptides, improves HUVEC attachment and growth in a static environment.

Amino Acid Sequence↗

PubMedDate not supplied

Bacterial adhesion on polyurethane surfaces conditioned with thrombus components.

Thrombosis and infection are two major complications associated with cardiovascular devices such as ventricular assist devices, total artificial hearts, vascular grafts, and catheters. When blood contacts an artificial biomaterial, protein deposition occurs, as do activation of the blood coagulation cascade, platelet adhesion, activation, and aggregation, all of which lead to thrombus formation. An increased incidence of bacterial infection also has been seen clinically with indwelling biomaterial devices. Some evidence suggests a possible association between thrombosis and infection, in that adherent bacteria may provide a nidus for thrombus formation, or adherent thrombi composed of platelets and fibrin may form sheltered sites for bacterial adhesion. In the current study, the authors examined Staphylococcus aureus adhesion to sulfonated, aminated, and phosphonated polyurethane surfaces that had been pre-adsorbed with solutions of increasing complexity, in an effort to approach and simulate clot formation on the surface. These solutions included various combinations of fibrinogen, albumin, plasma, thrombin, and isolated platelets. Bacterial adhesion was observed in a radial flow chamber mounted on the motorized stage of a video microscopy system, with image processing software used to perform automated data collection and image analysis. Scanning electron microscopy also was used to visualize cross-linked fibrin and bacterial adhesion on these surfaces. Bacterial adhesion was found to be lowest on the phosphonated polyurethane. The presence of fibrin or isolated platelets significantly increased bacterial adhesion compared to surfaces pre-adsorbed with albumin.

Bacterial Adhesion↗

PubMedDate not supplied

A capillary method to measure water transmission through polyurethane membranes.

A capillary method has been developed to measure the rate of water transmission through polyurethane membranes prepared for use as ventricles in artificial hearts. The system consisted primarily of a leak-proof sample chamber containing the water, a glass capillary flow meter, and a receiver compartment with continuous dry air ventilation. The capillary flow meter monitored the volume of water loss in the sample chamber. The rate of water transmission through the test membrane was found to be proportional to the water loss in the sample chamber, and dependent on the membrane thickness. For thicknesses from 0.09 mm to 0.34 mm, water vapor transmission rates ranged from 7.53 x 10(-8) to 2.76 x 10(-8) mol/s cm2, respectively. Although the concentration of water vapor in the receiver compartment did affect the rate of water vapor transmission through the membrane, within the pressure range 50-200 mmHg, there was very little effect. These findings suggest that water transmission through a polyurethane membrane is dominated by a diffusion process rather than by bulk convection.

Biocompatible Materials↗

PubMedDate not supplied

Long-term experience with polyurethane, pail handle, coiled tip peritoneal dialysis catheters.

Long-term experience with 63 polyurethane, pail handle, coiled tip peritoneal dialysis catheters surgically implanted in 57 consecutive patients with renal failure is presented. One hundred percent follow-up of the study group represented 1,248 patient-months of observation. Cumulative catheter survival rates were 80.8% at 12 months, 62.3% at 24 months, and 48.1% through 51 months. Catheter half-life was 32.6 months. Infection was the most frequent catheter related complication. Incidence rate of peritonitis was 0.73, and exit site/tunnel infection was 0.42 episodes per patient-year. Median time to first episode was 11.7 months for peritonitis, and 26.3 months for exit site/tunnel infection. Infection led to removal of 28.6% of implanted devices, mechanical blockage resulted in 6.4% loss, and pericatheter leak and tubing break each accounted for 1.6% of catheter removals. The polyurethane, pail handle, coiled tip peritoneal catheter was found to be a reliable long-term access device compared with reported performances of other catheter types. An adverse outcome was identified in the current clinical series with a model design using a permanently attached catheter adapter that caused large exit site wounds that were predisposed to infection and catheter loss.

Adolescent↗

PubMedDate not supplied

Development of infection resistant polyurethane biomaterials using textile dyeing technology.

Infection is a major complication when using biomaterials such as polyurethane in the clinical setting. The purpose of this study was to develop a novel infection resistant polyurethane biomaterial using textile dyeing technology. This procedure results in incorporation of the antibiotic into the polymer, resulting in a slow, sustained release of antibiotic from the material over time, without the use of exogenous binder agents. Polycarbonate based urethanes were synthesized that contained either a non-ionic (bdPU) or anionic (cPU) chain extender within the polymer backbone and cast into films. The fluoroquinolone antibiotic ciprofloxacin (Cipro) was applied to bdPU and cPU using textile dyeing technology, with Cipro uptake determined by absorbance reduction of the "dyebath." These dyed bdPU/cPU samples were then evaluated for prolonged Cipro release and antimicrobial activity by means of spectrophotometric and zone of inhibition assays, respectively. Cipro release and antimicrobial activity by dyed cPU segments that were aggressively washed persisted over 9 days, compared with dyed bdPU and dipped cPU control segments that lasted < 24 hours. Dyed cPU segments, which remained in a static wash solution, maintained antimicrobial activity for 11 days (length of study), whereas controls again lost antimicrobial activity within 24 hours. Thus, application of Cipro to the cPU polymer by means of dyeing technology results in a slow sustained release of antibiotic with persistent bacteriocidal properties over extended periods of time.

Anti-Infective Agents↗

PubMed1982

Disappearance of the polyurethane cover of the Ashley Natural Y prosthesis.

Polyurethane foam implanted in our patient was neither inert nor permanent. Clinical observations and animal studies suggest that all polyurethanes implanted to date have slowly disintegrated and have been absorbed in tissue. This process takes several years to complete. The exact time sequence and histology are not known.

Breast↗

PubMed1986

Late breast pain following reconstruction with polyurethane-covered implants.

Two patients of 56 who were reconstructed with polyurethane-coated implants developed breast pain as a late complication and eventually required implant removal for relief. Although the cause of pain was not proven, it may have been due to contracture of the fibrous capsule which formed between the polyurethane and the shell of the implant. The complication of late pain has not been stressed previously in the literature on reconstruction.

Adult↗