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PubMed1983

Thermoplastic polyurethanes as insulating materials for long-life cardiac pacing leads.

Historically, the material most widely used for permanent cardiac pacing lead insulation has been silicone elastomer. We have recently evaluated a variety of polyether polyurethanes and found them also to be suitable as insulating materials for cardiac pacing leads. Test results showed that these polyurethanes are extremely tough, hydrolytically very stable, non-toxic, non-carcinogenic, and very inert in a biological environment. In addition, because polyurethane has a higher tensile strength than silicone elastomer, a thinner insulating layer can be used to construct smaller diameter leads. This facilitates the introduction of one or two leads through small veins or split sheath introducers. The smooth polyurethane material is also very easy to advance through the venous circulation, thus improving the handling characteristics of the lead or leads.

Animals↗

PubMed1986

Long-term performance of polyurethane pacing leads: mechanisms of design-related failures.

Environmental stress cracking has been identified as a crack propagating mechanism in polyurethane-insulated, heart pacemaker leads, which is directly related to specific lead design parameters. Lead designs imposing excessive stress on the polyurethane insulation through an interference fit between the coil and polymer have demonstrated insulation failures. Conversely, low-stress designs have shown virtually no insulation problems. The higher-stress designs have used organic solvents to facilitate coil placement during manufacturing, which may result in lowering the polymer's ability to resist the higher stress. In addition, a specific silver-containing coil wire composition has been found to galvanically corrode upon body fluid intrusion into the lead, ionizing the silver. These ions interact with the polyurethane polymer resulting in the loss of polymer strength. All polyurethane lead failures to date have been specific to high stress and/or chemical interaction. Leads using low-stress designs and nonreactive coil wire compositions continue to demonstrate a positive clinical experience.

Animals↗

PubMed2004

Cancer incidence and mortality of isocyanate exposed workers from the Swedish polyurethane foam industry: updated findings 1959-98.

AIMS: To assess whether cancer incidence and mortality in chronic obstructive lung diseases were increased in the Swedish polyurethane foam industry cohort, updated with 11 more years of follow up. METHODS: The mortality and cancer incidence (1959-98) experienced by a cohort of 4175 male and female employees employed for at least one year in the period 1959-87 at one of nine Swedish polyurethane foaming plants were investigated. Comparisons were based on calendar year, sex, and five-year age group specific mortality and incidence rates for Sweden. Workplaces and job tasks were categorically assessed for exposure to toluene diisocyanate (TDI) and methylene diphenyldiisocyanate (MDI) by occupational hygienists. RESULTS: Fewer cancer cases than expected were observed, but the lung cancer incidence was enhanced in women. Women with "apparent exposure" to TDI or MDI did not, however, have a higher lung cancer incidence than those with "no or low exposure". Moreover, a nested case referent study did not find that polyurethane dust exposure had been more prevalent among the female lung cancer cases than among referents. No increased mortality in chronic obstructive lung diseases was observed in the cohort. CONCLUSIONS: Results support the findings from two other cohort studies of an increased lung cancer risk among female workers in the polyurethane foam manufacturing industry. Chance or confounding from smoking are not obvious explanations for the coherent findings. However, the study was not able to link isocyanate exposed employment with lung cancer risk.

Adult↗

PubMed2003

Obstruction of the lacrimal system: treatment with a covered, retrievable, expandable nitinol stent versus a lacrimal polyurethane stent.

PURPOSE: To compare the clinical effectiveness of a covered nitinol stent with that of a polyurethane stent for treatment of lacrimal system obstructions. MATERIALS AND METHODS: A nitinol stent was knit from a single thread of 0.1-mm nitinol wire in a tubular configuration and was covered by dipping the stent into a polyurethane solution. The stent was 4 mm in diameter and 30 or 35 mm long. With fluoroscopic guidance, a covered nitinol stent (n = 33, group A) or a polyurethane stent (n = 35, group B) was placed in 68 patients. The following items were evaluated retrospectively: technical success, procedure time, cumulative patency rate, and complications. An unpaired Student t test was used to analyze the difference between the procedure times. Kaplan-Meier survival curves and a log-rank test were used to compare the cumulative patency rates. RESULTS: Stent placement was technically successful in 31 (94%) of 33 patients in group A and in all 35 (100%) patients in group B. After stent placement, all patients showed resolution of epiphora. Average procedure time was 400 seconds (range, 270-900 seconds) in group A and 260 seconds (range, 150-900 seconds) in group B. The difference between the procedure times was statistically significant (P =.0003). During the mean follow-up period of 40 months, there was recurrence of epiphora in 30 of 31 patients in group A and 26 of 35 patients in group B. The difference of the cumulative patency rates was statistically insignificant (P =.2). CONCLUSION: Although the polyurethane stent used for treatment seemed to be more effective than the nitinol stent, selection of these stents for placement should be made with caution, because the long-term patency rates are not encouraging.

Adolescent↗

PubMed2003

Compression-induced changes on physical structures and calcification of the aromatic polyether polyurethane composite.

It is generally accepted that stress causes calcification in both bio-prosthetic and polyurethane heart valves. However, simple uni-axially- and bi-axially-stretched samples did not yield a feasible model for the elaboration of the stress-induced calcification. In this study, heat compaction combined with the incorporation of polyethylene has been explored. Specimens of polyurethane were solution cast onto a porous bi-axially-drawn ultra-high-molecular-weight polyethylene film and then heat compacted under a pressure of 18 MPa at a chosen temperature for 1.5 h. The heat-compaction-induced calcification and physical changes of the polyurethane composite were evaluated using a 28-day in vitro calcification model and Attenuated Total Reflection-Fourier Transform-Infrared (ATR-FT-IR) spectroscopy. The calcification results indicated that heat-compaction-induced calcification was double that achieved without heat compaction. Heat-compacted polyurethane composite showed higher affinity to calcium ions than the non-heat compacted sample. The ATR-FT-IR results showed that the heat-compaction-induced physical changes include distortions of polymeric molecules and permanent changes of microstructures. The distortions of polymeric molecules could be deteriorated in contact with different media. The relaxation of the stressed structures of the polyether moiety might serve as a calcium trap and a heterogeneous nucleation site for calcification. The permanent changes of microstructures resulted from high distortions also served as affinity sites attracting calcification.

Biocompatible Materials↗

PubMed1996

A new method for continual quantitation of viable cells on endothelialized polyurethanes.

Many of the segmented polyurethanes currently used in cardiovascular prostheses undergo either modification of their surface structure or are lined with a confluent monolayer of endothelial cells to improve their hemocompatibility. During the establishment of an endothelial cell lining on these biopolymers it is necessary to continually monitor the number of viable cells that are covering the substrate. Yet, not all of the conventional cell enumeration techniques are suitable for assessing the growth of endothelial cells on polyurethanes. Methods, such as direct cell counting, dye uptake, or DNA or protein staining require either a transparent scaffold or lead to termination of the culturing process prior to measurement. In addition, some of the spectroscopic assays are often hampered by interaction of the dyes and/or solubilizers with the various constituents (e.g., catalyzers, antioxidants) and/or functional groups in the polyurethane formulations. In addressing these problems, we adapted a novel, highly reproducible fluorescent assay which is based on reduction by viable cells of an electrochemically sensitive compound, Alamar Blue. The bioreduced product is soluble and stable in culture media and noncytotoxic. In addition, the assay is independent of the geometry or physicochemical properties of the polymeric surfaces. In the present study we focus on the implementation of this assay to monitoring attachment and growth of various endothelial cell types on segmented polyurethanes.

Analysis of Variance↗

PubMedDate not supplied

Cuff Cath: an initial experience of cuffed polyurethane central venous catheters in children.

The tendency of medium- and long-term silicone central venous catheters (CVCs) to block, fracture, and become displaced has led to the evaluation of a polyurethane CVC, Cuff Cath (Viggo Spectramed, Swindon, Wilts, United Kingdom) as a possible alternative because polyurethane is smoother and stronger. We report the first prospective study of polyurethane cuffed CVCs in children. Sixty Cuff Caths were placed in 53 children, mean age 4.7 years (range, 4 days to 16.3 years), mean weight 15.6 kg (range, 3.1 to 58 kg). All CVCs were tunnelled (mean tunnel length, 12 cm; range, 5 to 20 cm) and inserted either into the subclavian vein (n = 28) or internal jugular vein (n = 32). In a total of 6363 catheter days (mean, 111 days per patient; range, 15 to 364 days), three (5%) CVCs had to be removed because of sepsis and one (2%) because of blockage. All other Cuff Caths remained patent to infusion and blood sampling. No Cuff Caths were pulled or fell out, fractured, or migrated. This study demonstrates significant advantages of polyurethane compared with previous series using silicone CVCs with respect to blockage, fragmentation, and dislodgement. A prospective, randomized, controlled trial of Cuff Cath compared with a silicone CVCs in children is required.

Adolescent↗

PubMed1987

Antithrombogenic heparin-bound polyurethanes.

Many kinds of heparin-bound polyurethanes have been developed. Polyurethanes are a family of elastomers displaying better blood-compatibility than other polymeric materials. It is useful to modify this material by heparinization. Several approaches to heparinization have been devised: 1) a general method of heparinization, applicable to all polymeric materials, 2) a heparinization method specific to polyurethanes, and 3) the design of heparinizable polyurethane derivatives. These three approaches are first explained in detail. Then, the antithrombogenic mechanism of the heparinized polymers is discussed. Finally, the interactions of the heparinized polymers with blood coagulation factors, plasma proteins, and platelets are discussed.

Biocompatible Materials↗

PubMed2003

In-vitro and in-vivo antibacterial activity evaluation of a polyurethane matrix.

Various in-vitro and in-vivo methods for evaluation of the duration of antibacterial activity were compared using a controlled-release polyurethane matrix developed for the prevention of surface bacterial adhesion and growth. Cefadroxil was incorporated into this polyurethane matrix by a solvent casting method before the matrix was coated with polyurethane in tetrahydrofuran solution. The release of cefadroxil from the matrix into distilled water at 37 degrees C was measured by HPLC. The morphological change of matrices before and after release studies was investigated by scanning electron microscopy (SEM). The duration of antimicrobial activity of the matrix against Escherichia coli and Staphylococcus aureus was evaluated by measuring the diameters of the inhibition zone and the optical density of the broth. The matrices were also implanted subcutaneously in rats and the duration of the antibacterial activity was determined by measuring the inhibition zone. The results showed that duration of antibacterial activity of the polyurethane matrix was successfully determined in-vitro by these methods, and the results differed from the conventional in-vitro release study. It was also possible to determine the duration of action of the matrix in-vivo by implanting the matrix in rats, and then measuring the antibacterial activity of the matrix at predetermined time intervals. While a good correlation was observed between the in-vitro and in-vivo methods used in this study to evaluate the duration of the antibacterial activity of the polymeric matrix, the conventional in-vitro release study did not coincide with these results.

Animals↗

PubMedDate not supplied

Evaluation of an aliphatic polyurethane as a microsphere matrix for sustained theophylline delivery.

In spite of several biomedical applications of polyurethanes, very little attention has been focused on these polymers for controlled drug delivery. In this study, an aliphatic polyurethane, Tecoflex, was evaluated as a microsphere matrix for the controlled release of theophylline. Polyurethane microspheres containing theophylline were prepared using a solvent evaporation technique from a dichloromethane solution of the polymer containing the drug. A dilute solution of poly(vinyl alcohol) served as the dispersion medium. Microspheres of good spherical geometry having theophylline content of 35% could be prepared by the technique. The release of the drug from the microspheres was examined in simulated gastric and intestinal fluids at 37 degrees C. While a large burst effect was observed in gastric fluid, in the intestinal fluid a close to zero-order release was seen. Attempts were made to modulate the release by incorporating poly(ethylene glycol) in the matrix and also coating the spheres with paraffin wax. Preliminary data indicate that polyurethanes could be interesting matrices for controlled drug delivery.

Chemistry, Pharmaceutical↗

PubMed1992

Biostable polyurethane elastomers.

The generic term polyurethane represents the most versatile family of synthetic polymers. The unsurpassed physical and chemical properties of polyurethanes, coupled with their biocompatibility, have led to their use in a wide range of biomedical applications. Although polyurethanes have been shown to be stable in vitro for many years, they can undergo rapid microcracking when implanted. These microcracks not only weaken the polymer but also serve as nucleation sites for thrombus formation and lead to catastrophic failure. In this article, the authors report on the development and testing of a new ether-free polyurethane that does not exhibit surface microcracking under accelerated in vivo condition.

Animals↗

PubMedDate not supplied

Exit-site care with ciprofloxacin otologic solution prevents polyurethane catheter infection in peritoneal dialysis patients.

OBJECTIVE: Mupirocin ointment and antiseptics are standard cleansing agents in routine exit-site care of peritoneal dialysis (PD) catheters, but these agents have a deleterious effect on polyurethane devices. We assessed the effectiveness of topical use of ciprofloxacin otologic solution for preventing exit-site infection (ESI) in PD patients with polyurethane catheters. DESIGN: Prospective study. SETTING: Service of Nephrology of an acute-care teaching hospital in Galdácano, Bizkaia, Spain. PATIENTS: A total of 164 patients with polyurethane catheters inserted was studied from start of continuous ambulatory PD to the end of a 24-month period. Patients were divided into two groups according to exit-site treatment protocols. INTERVENTION: Patients in group 1 (n = 86) were instructed on daily exit-site care with soap and water only; whereas patients in group 2 (n = 78) cleansed with soap and water, followed by application of a single-dose vial of 0.5 mL ciprofloxacin (1 mg) for application around the insertion site. MAIN OUTCOME MEASURES: Episodes of ESI and peritonitis. RESULTS: There were 67 episodes of ESI among patients in group 1 versus 9 episodes among patients in group 2 (p < 0.05), resulting in a rate of 0.41 and 0.06 episodes per patient-year of exposure, respectively (p < 0.001). Staphylococcus aureus ESI rate was 0.34 in group 1 versus 0.06 in group 2 (p = 0.001). Infections caused by Pseudomonas aeruginosa and other pathogens occurred in 11 patients in group 1 and in no patients in group 2 (p = 0.05). Peritonitis due to S. aureus ESI was significantly less frequent among patients treated with ciprofloxacin (1 vs 9 cases, p = 0.001). Removal of the catheter was necessary in 5 patients in group 1 and in no patients in group 2 (p < 0.05). CONCLUSION: Daily application of ciprofloxacin otologic solution at the exit site of PD patients with polyurethane catheters inserted significantly reduces the rate of ESI caused by S. aureus and other organisms, particularly P. aeruginosa.

Anti-Infective Agents↗

PubMed2002

[The advance of research for biocompatibility of medical polyurethanes].

Polyurethanes are popularly used in cardiovascular and other biomedical fields due to their good biocompatibility as well as mechanical properties. But they are subject to biodegradation in vivo for a long time, and cause inflammation, so improving the biocompatibility of medical polyurethanes is an important subject of biomaterials. Recent researches have focused on biological modelling of biomaterials for improving the biocompatibility of polyurethanes. This paper reviews two main methods for improving biocompatibility of polyurethanes-endothelial cells seeding and mimic biomembrane (phospholipid surface), and summarizes the main procedures and questions of these two methods.

Biocompatible Materials↗

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↗