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At least 325 records · Page 18Linked to original sources

PubMed2000

Artifacts recorded through failing bipolar polyurethane insulated permanent pacing leads.

Pacing failure in bipolar systems using polyurethane insulated leads may be frequent depending on the type of polyurethane and can cause oversensing and or failure to capture. The reason for this failure is often breakage in the inner insulation. The aim of this study was to evaluate the signals created by such a short circuit. Thirty-seven patients were included in the study, 13 with failing leads with polyurethane 80A insulation, 14 with old but normally functioning leads and 10 patients with new leads. Artifacts in the form of spikes were recorded, during surgical revision, from 11 patients with failing leads (84.6%). In patients with normally functioning leads and newly implanted leads no artifacts were recorded. A significant decrease in impedance of 373.4 Ohms (99% confidence intervals 286.4-460.4, P<0.05) was noted in the failing leads compared with a decrease of only 113.0 Ohms (99%, confidence intervals 6.5-219.6, P<0.01) in the control leads. The difference between the groups was highly significant. In 10 newly implanted and five normally functioning bipolar ventricular leads similar artifacts could be created by making intermittent contact between the proximal lead connections. Thus, artifacts could be recorded from failing leads and from intact leads with artificial intermittent connection at the proximal end. Our results suggest that the failure is caused by a short circuit in the lead. This finding may have important clinical applications in the follow-up of bipolar pacing and defibrillation leads.

Aged↗

PubMed1985

[Clinical experiences with polyurethane soft foam fillings for retinal surgery].

Polyurethane sponge was used for scleral buckling in 165 patients suffering from retinal detachment. This material showed good tissue compatibility and the therapeutic procedure was successful in 90% of the cases thus treated. In 10 patients polyurethane was used with success for cerclage. Postoperative complications observed were infection of the sponge in one patient and conjunctival dehiscence in two. Polyurethane sponge is less elastic than silicone sponge but has the same scleral buckling effect.

Adolescent↗

PubMed2002

Polyurethane-covered metal stent for management of distal malignant biliary obstruction.

BACKGROUND: The efficacy of polyurethane-covered metal expandable stents for treatment of neoplastic distal biliary obstruction was analyzed. METHODS: Twenty-one patients with unresectable malignant tumors involving the mid to distal bile duct who were seen with obstructive jaundice were consecutively enrolled. Eighteen patients underwent endoscopic implantation of a polyurethane-covered metal stent and 3 patients underwent transhepatic insertion because of duodenal obstruction. The stent patency, complications, and patient survival were analyzed. RESULTS: Effective biliary decompression was achieved in all patients. Adverse events were minor: mild pancreatitis (1) and cholecystitis (2) occurred within 7 days of stent insertion. Mean survival and stent patency were 233 days and 206 days, respectively. Stent occlusion occurred in 3 patients (14%) after a mean of 188 days. Tumor ingrowth through the stent mesh was not observed. However, 2 stents were occluded by tumor overgrowth and 1 by compacted alimentary debris. CONCLUSIONS: A polyurethane membrane may prevent tumor ingrowth and reduce the occlusion rate for expandable metal stents implanted in patients with malignant obstruction of the distal bile duct.

Adult↗

PubMed2004

In vitro assessment of chlorhexidine gluconate-impregnated polyurethane foam antimicrobial dressing using zone of inhibition assays.

OBJECTIVE: To evaluate an antimicrobial dressing consisting of hydrophilic polyurethane foam with chlorhexidine gluconate for activity against several antibiotic-resistant clinical isolates as well as American Type Culture Collection reference strains using zone of inhibition assays. METHODS: Sterile foam samples with chlorhexidine gluconate and untreated controls were transferred onto inoculated agar plates. Plates were incubated at 35 degrees C to 37 degrees C for 24 hours and examined for zones of inhibition around the foam samples. RESULTS: Polyurethane foam with chlorhexidine gluconate showed antimicrobial activity in vitro against all of the challenge organisms including antibiotic-resistant clinical isolates. CONCLUSION: The data from this in vitro study support the hypothesis that polyurethane foam with chlorhexidine gluconate has an antimicrobial effect against antibiotic-resistant Staphylococcus and Enterococcus species, as well as Candida species.

Anti-Infective Agents, Local↗

PubMed2006

Assessing isocyanate exposures in polyurethane industry sectors using biological and air monitoring methods.

Isocyanates, as a chemical group, are considered to be the biggest cause of occupational asthma in the UK. Monitoring of airborne exposures to total isocyanate is costly, requiring considerable expertise, both in terms of sample collection and chemical analysis and cannot be used to assess the effectiveness of protection from wearing respiratory protective equipment (RPE). Biological monitoring by analysis of metabolites in urine can be a relatively simple and inexpensive way to assess exposure to isocyanates. It may also be a useful way to evaluate the effectiveness of control measures in place. In this study biological and inhalation monitoring were undertaken to assess exposure in a variety of workplaces in the non-motor vehicle repair sector. Companies selected to participate in the survey included only those judged to be using good working practices when using isocyanate formulations. This included companies that used isocyanates to produce moulded polyurethane products, insulation material and those involved in industrial painting. Air samples were collected by personal monitoring and were analysed for total isocyanate content. Urine samples were collected soon after exposure and analysed for the metabolites of different isocyanate species, allowing calculation of the total metabolite concentration. Details of the control measures used and observed contamination of exposed skin were also recorded. A total of 21 companies agreed to participate in the study, with exposure measurements being collected from 22 sites. The airborne isocyanate concentrations were generally very low (range 0.0005-0.066 mg m(-3)). A total of 50 of the 70 samples were <0.001 mg m(-3), the limit of quantification (LOQ), therefore samples below the LOQ were assigned a value of 1/2 LOQ (0.0005 mg m(-3)). Of the 70 samples, 67 were below the current workplace exposure limit of 0.02 mg m(-3). The highest inhalation exposures occurred during spray painting activities in a truck manufacturing company (0.066 mg m(-3)) and also during spray application of polyurethane foam insulation (0.023 mg m(-3)). The most commonly detected isocyanate in the urine was hexamethylene diisocyanate, which was detected in 21 instances. The geometric mean total isocyanate metabolite concentration for the dataset was 0.29 micromol mol(-1) creatinine (range 0.05-12.64 micromol mol(-1) creatinine). A total of 23 samples collected were above the agreed biological monitoring guidance value of 1.0 micromol mol(-1) creatinine. Activities that resulted in the highest biological monitoring results of the dataset included mixing and casting of polyurethane products (12.64 micromol mol(-1) creatinine), semi-automatic moulding (4.80 micromol mol(-1) creatinine) and resin application (3.91 micromol mol(-1) creatinine). The biological monitoring results show that despite low airborne isocyanate concentrations, it was possible to demonstrate biological uptake. This tends to suggest high sensitivity of the biological monitoring method and/or that in some instances the RPE being used by operators was not effective or that absorption may have occurred via dermal or other routes of exposure. This study demonstrates that biological monitoring is a useful tool when assessing worker exposure to isocyanates, providing a more complete picture on the efficacy of control measures in place than is possible by air monitoring alone. The results also demonstrated that where control measures were judged to be adequate, most biological samples were close to or < 1 micromol mol(-1) creatinine, the agreed biological monitoring benchmark.

Air Pollutants, Occupational↗

PubMed1992

The polyurethane foam covering the Même breast prosthesis: a biomedical breakthrough or a biomaterial tar baby?

Because controversy continues to surround the implantation of the polyurethane foam-covered Même breast prosthesis, in vitro experiments were conducted to determine: (1) whether the polyurethane foam contains extractable toluene diamine isomers (TDAs), and (2) whether the polyurethane foam releases TDAs on exposure to mild hydrolytic conditions. Results confirmed the presence of extractable TDAs and other impurities in the foam covering the unused Même prosthesis, and that the concentrations of these impurities could be significantly reduced by washing the foam in a regular detergent. This washing step was omitted from the manufacturer's production process. Furthermore, on exposure to mild alkalis, the foam exhibited significant degradation, rapid fragmentation, loss of mechanical strength and physical integrity, as well as the release of additional TDAs. Because of the potential long-term risks associated with the release of TDAs in vivo, continued clinical use of the Même prosthesis containing this particular type of foam appears questionable.

Biocompatible Materials↗

PubMed1992

Polyurethane-covered mammary implants: a 12-year experience.

Polyurethane-covered mammary implants are the implants of choice in aesthetic and reconstructive mammary surgery. These implants give very good results in regard to breast contour and consistency, and have a very low complication rate. We present our 12-year experience using polyurethane-covered prostheses. We place the implant mostly in the subglandular or subcutaneous site, and their capsular contracture rate is extremely low (3.3%). Based on our experience, we also review the other complications and side effects occurring with polyurethane prostheses and discuss them in detail.

Breast↗

PubMedDate not supplied

Hemodynamic comparisons of polyurethane trileaflet and bioprosthetic heart valves.

Hemodynamic comparison of two polyurethane prosthetic heart valves with a bioprosthetic valve is presented. The valves were incorporated in a pulse duplicator simulating physiologic pulsatile flow, and comparisons between the valves were made on the transvalvular pressure drop, percent regurgitation, valve orifice area, rate of opening and closing as well as the performance index. The results showed that the functional characteristics of the polyurethane valve compared favorably with that of the bioprosthetic valve. The polyurethane valve can be a viable and inexpensive alternative, especially for short-term use in a total artificial heart as a bridge to transplant.

Bioprosthesis↗

PubMedDate not supplied

Assessment of the in vitro transport parameters for ethanehydroxy diphosphonate through a polyurethane membrane. A potential refillable reservoir drug delivery device.

Calcification (CALC) is the most frequent cause of failure in bioprosthetic heart valves (BHV) fabricated from glutaraldehyde pretreated porcine aortic valve or bovine pericardium. Site specific controlled administration of ethanehydroxy diphosphonate (EHDP), using numerous carriers, has been successful in inhibiting CALC of BHV tissue in an accelerated rat subdermal model, without adverse effects on serum calcium, bone development, or overall somatic growth. The current study was designed to evaluate refillable reservoir devices fabricated from polyurethane (Biomer Woburn, MA) with regard to their transport properties relative to EHDP. The refillable reservoirs were evaluated for EHDP release in vitro at 22 degrees C (under perfect sink conditions) into both a physiologic receptor phase (N-2 hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer, pH = 7.4) with (1.5 mM) or without Ca2+ present. Transport parameters for EHDP diffusion through the polyurethane membranes used to fabricate the reservoirs were significantly different for the two receptor phases evaluated. The mean diffusion coefficients (D) for EHDP through the polyurethane membrane into each receptor phase were not significantly different. However, an approximately 3.5-fold reduction was observed in the mean value of the partition coefficient (K) for EHDP when EHDP was evaluated for release into a receptor phase that contained 1.5 mM Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1981

Clinical experience with polyurethane-covered gel-filled mammary prostheses.

We have used 104 low-profile polyurethane-covered gel-filled mammary prostheses in 54 patients. Only one patient has developed capsular contracture. Foreign-body reaction to polyurethane was clinically significant in only one patient. Other complications have been few and of the type that can accompany any type of mammary prosthesis. Of the 54 patients studied, 51 still have their implants in place and have soft, compressible breasts. The superior wrinkling and palpable implant edge that is occasionally present when the implant is placed subcutaneously has been of some concern to patients and can be eliminated by submuscular placement. The use of polyurethane-covered low-profile gel-filled prostheses for breast reconstruction has greatly improved our results, and the satisfaction of both surgeon and patient has been gratifying.

Breast↗

PubMed1984

Reconstruction of the breast using polyurethane-coated prostheses.

We have inserted 302 Natural-Y polyurethane-coated implants in 92 patients. Follow-up time for the cases studied ranges from 6 months to 41/2 years after reconstruction. None of our patients was observed to develop capsular contracture, and the foreign-body reaction to the polyurethane was of no clinical significance when the implants were placed in a total muscle pocket. Four cases of ruptured prostheses were observed. Overall, the excellent aesthetic results of the polyurethane-coated prostheses were encouraging, resulting in soft, natural-feeling, and aesthetically pleasing breasts.

Breast↗

PubMed1998

Late capsular hematoma after breast reconstruction with polyurethane-covered implants.

We report two patients who developed late hematomas after breast reconstruction with polyurethane-covered implants. Although the cause of these hematomas is not absolutely clear, they are believed to have been caused by the intense, highly vascular inflammatory response that polyurethane coating is known to elicit. The development of late hematoma has not been previously stressed in the literature as a late complication of polyurethane-covered breast implants.

Adult↗

PubMed2003

Flared polyurethane-covered self-expandable nitinol stent for malignant biliary obstruction.

PURPOSE: To determine the technical efficacy and safety of a flared polyurethane-covered self-expandable nitinol stent in the management of malignant biliary obstruction and to evaluate its clinical efficacy by estimating stent patency and patient survival rates. MATERIALS AND METHODS: Thirteen patients with common bile duct strictures (nonhilar) caused by malignant disease were treated by placement of 13 nitinol stents. The stents used include a flared section in the proximal portion (12 mm in diameter and 10 mm in length) and a section in the remnant portion that is fully covered with high-elasticity polyurethane, with an unconstrained diameter of 10 mm and a total length of 50-80 mm. Patient survival and stent patency rates were calculated with use of Kaplan-Meier survival analysis. The follow-up bilirubin and serum amylase and lipase levels were calculated, and the differences in means were evaluated with use of a Wilcoxon signed-rank test. The average follow-up duration was 22.9 weeks (range, 8-56 weeks). RESULTS: Placement was successful in all cases. The 30-day mortality rate was 0%. The survival rates were 38% and 24% at 20 and 50 weeks, respectively. Seventy-seven percent of study patients had adequate palliative drainage during their the remainder of their lives. The stent patency rates were 71% and 48% at 20 and 50 weeks, respectively. Three patients (23%) presented with stent occlusion requiring repeat intervention. There were no procedure-related complications such as proximal or distal migration. No complications occurred other than stent occlusion. One patient's stent was removed under endoscopic guidance 15 weeks after its insertion. Bilirubin levels had significantly decreased 1 week after stent insertion (P <.001). CONCLUSION: Preliminary results suggest that placement of a flared polyurethane-covered self-expandable nitinol stent is feasible and effective in achieving biliary drainage. The stents do not migrate, but there is tumor ingrowth into the flared portion of the stent. Treatment of a larger group of patients will be mandatory to validate these long-term results.

Adult↗

PubMed2006

First development of a polyurethane keratoprosthesis and its Australian connection: an unbeknown episode in the history of artificial cornea.

This paper is aimed at establishing a particular chronological priority issue in the convoluted history of artificial cornea. According to existing records, the first keratoprosthesis made from polyurethane was developed by Caldwell and Jacob-Labarre in the late 1980s. This paper demonstrates that in fact the first polyurethane keratoprosthesis was proposed and designed in 1985 by Lawrence Hirst, an Australian ophthalmologist then working in St Louis, USA. The first prototype was manufactured in January 1986 by Thermedics Inc according to Dr Hirst's instructions from Tecoflex, a transparent polyurethane developed by the same company. This keratoprosthesis, which also had a porous skirt, was inserted intralamellarly in a monkey cornea and followed up clinically for about 3 months. There were no significant postoperative complications, and the histology of the explant indicated proper biointegration of the prosthetic skirt within the host stromal tissue. Because of a delay in the manufacture of further prototypes and to Dr Hirst's decision to return to Australia, the project was eventually abandoned. As no report was published on this development, the present paper is entirely based on original documents held in Dr Hirst's archives.

Artificial Organs↗

PubMed1995

Fracture of polyurethane double pigtail stents: an in vivo retrospective and prospective fluoroscopic study.

OBJECTIVE: To study the behaviour of pigtail polyurethane ureteric stents during breathing and change in body habitus and thereby explain some side-effects of stenting, particularly spontaneous stent fracture. PATIENTS AND METHODS: The study comprised retrospective evaluation of records and radiographs of seven patients (five men and two women, mean age 41; SD 10.9 years) who were admitted with fractured polyurethane pigtail stents, and a prospective fluoroscopic study of the behaviour of 14 stents in 12 patients (11 men and one woman; mean age 40; SD 9.3 years) during breathing, spinal flexion, extension and rotation. RESULTS: Five of the seven pigtail stents fractured where the stent crossed the lateral edge of psoas muscle, 7-10 cm below the renal coil of the stent. The sixth stent was fractured at its lower third and the seventh fractured just proximal to the stent's bladder coil. The prospective study revealed a 20-80 degrees bend in the upper third of 11 of the 14 stents and a 35 degrees bend in the lower third of two stents. A 1-5 cm craniocaudal movement and a 0-2 cm vertical movement of the stents occurred during breathing and spinal flexion and extension. There were no changes in stent configuration during spinal lateral rotation or at the sacral promontary. The bend in the upper third of the ureter was profound in two stents whose vertical movement was restricted by other conditions. CONCLUSION: As the kidney-to-bladder distance shortens during inspiration and spinal flexion, the stent adapts by bending and/or moving. Fracture of the stent may be caused by repeated mechanical stress, particularly across the side-holes, and by diminution of its tensile strength by depolymerization during long indwelling times. Large polyurethane stents tended to bow, displacing the upper ureter anteriorly, while small, soft stents conformed to the anatomical course of the ureter, suggesting that they should be used after open or endoscopic surgery to the upper two-thirds of the ureter. Stress on the stent can be minimized by choosing the correct length, particularly where vertical stent movement is limited by other conditions.

Adult↗

PubMed1987

Albumin adsorption and retention on C18-alkyl-derivatized polyurethane vascular grafts.

The short-term albumin affinity and thrombo-resistance of a polyether polyurethane vascular graft have been improved. The method is based on the C18 alkylation of the polymer. Thrombus formation by a planimetric technique and albumin retention on wire-reinforced polyurethane tubes, both C18 alkylated and untreated, were measured in short-term (4-h) exposure at femoral arterial sites in the dog. 125I-Albumin was preabsorbed on tubes and then exposed to blood for successive 2-h periods. Albumin uptake on alkylated tubes prior to blood exposure and retention following 2 h of blood exposure were significantly greater than on controls. Following a fast desorption phase in blood, the remaining albumin was more slowly desorbed from alkylated than from control tubes. Reincubation with albumin and blood reexposure produced a similar tendency, suggesting blood conditioning does not reduce the albumin affinity-enhancing property of C18 alkylation in the short term. Blood-preconditioning experiments suggested endogenous albumin has a high affinity for the C18-alkylated surface. Scanning electron microscopic examination showed thrombus and platelet densities were higher on control than on alkylated surfaces. These results suggest in vivo albumin affinity is increased for C18-alkylated polyurethane, which may be linked to decreased thrombus formation on these surfaces.

Adsorption↗

PubMed1989

In vitro comparison of velocity profiles and turbulent shear distal to polyurethane trileaflet and pericardial prosthetic valves.

A comparative study of flow dynamics past biomer trileaflet valves and a pericardial bioprosthetic valve under steady and physiological pulsatile flow conditions in vitro is reported in this paper. The velocity profiles and the turbulent shear stresses distal to the valves were measured using laser Doppler anemometry. The authors' results showed that the velocity profiles distal to the trileaflet valves were similar to that measured distal to the pericardial valve. Higher magnitudes of absolute turbulent shear stresses were measured distal to the synthetic valves in comparison to the pericardial valves. However, when the stresses were nondimensionalized with respect to the orifice diameter at the inlet aspect, the stresses were comparable for all of the three valves. With design modifications to increase the orifice diameter at the inlet aspect of the polyurethane valves, the turbulent stresses distal to the valves can be minimized. Such in vitro studies on the flow dynamics past the polyurethane valves can provide information towards design changes to improve the performance characteristics of these valves. Polyurethane valves with flow characteristics comparable to the pericardial valves can be manufactured relatively inexpensively compared to mechanical or tissue valve prosthesis. Hence, the synthetic valves may be a viable alternative for short-term use in total artificial heart devices as a bridge to transplant.

Bioprosthesis↗

PubMed1996

Changes in polyurethane calcification due to antibiotics.

To develop artificial materials for prolonged use in the vascular system, the complicated process of surface-induced calcification must be better understood. Calcification was examined on porous polyurethane incubated in metastable solutions of calcium phosphate, and the role of certain antibiotics in the medium was evaluated. It seems that certain aminoglycoside antibiotics can modify polyurethane surfaces and, subsequently, their mineralization process. In addition, these antibiotics may alter the calcium transport through polyurethanes. Therefore, it is conceivable that certain antibiotics can, in addition to producing their antibacterial effect, modulate surface calcium binding by changing the calcium mobilization and crystallization. Additional studies are needed to develop applications.

Aminoglycosides↗