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At least 577 records · Page 32Linked to original sources

PubMed2006

Long-term follow-up of transvenous defibrillation leads: high incidence of fracture in coaxial polyurethane lead.

BACKGROUND: As a result of longer follow-up after implantation of cardioverter defibrillators (ICD), fatigue of the leads has become a concern. The aim of this study was to determine the incidence and clinical presentation of ICD lead failures. METHODS AND RESULTS: The study population consisted of 241 patients with 249 ICD leads who underwent implantation of an ICD with a transvenous lead system. After device implantation, the patients were routinely followed up every 4 months. Five lead failures (2.0%) occurred as an oversensing of artifact during the follow-up period (2.6+/-2.1 years); 4 of those 5 patients received inappropriate shocks and 1 case of lead failure was identified in a patient with frequent episodes of non-sustained ventricular fibrillation. In particular, the right ventricular polyurethane transvenous lead in the Medtronic model 6936 failed in 4 (13%) of 31 cases. Percutaneous lead extraction was not available in all cases, so an additional ICD lead was inserted through the same site of the subclavian vein. CONCLUSIONS: Lead failures may occur 5 years after ICD implantation and polyurethane leads have an especially high incidence of failure. However, there were no follow-up parameters observed that predicted lead failures.

Adult↗

PubMedDate not supplied

Removal of heavy metals from aqueous solution using Rhizopus delemar mycelia in free and polyurethane-bound form.

This study assesses the ability of mycelia of Rhizopus delemar (both free and immobilized on polyurethane foam) to remove heavy metals from single-ion solutions as well as from a mixture of them. All experiments were conducted using 0.5-5 mm solutions of CuSO4 x 5H2O, CoCl2-6H2O and FeSO4 7H2O. Mycelia immobilized on polyurethane foam cells showed some times increase in uptake compared with that of free cells. Metal ions accumulation from a mixed solution was decreased slightly for cobalt and iron and considerable for copper ions. Heavy metal uptake was examined in the immobilized column experiments and more than 92% heavy metal removal (mg heavy metals removed/mg heavy metals added) from a mixed solution was achieved during the 5 cycles. During these experiments, the dry weight of the immobilized cells was decreased by only 2%. These results showed that immobilized mycelia of Rhizopus delemar can be used repeatedly for removal of heavy metals from aqueous solutions.

Absorption↗

PubMed1998

Treatment of malignant biliary obstruction with polyurethane-covered Wallstents.

OBJECTIVE: This study was undertaken to determine the safety, efficacy, and performance of polyurethane-covered Wallstents in the treatment of malignant biliary obstruction. SUBJECTS AND METHODS: This pilot study included 30 patients with malignant biliary obstruction. Palliative decompression of the obstructed bile duct was attempted with a polyurethane-covered Wallstent that is a prototype. Patients with hilar obstructions were excluded. All stents were inserted percutaneously. Kaplan-Meier analysis was used to determine stent patency. RESULTS: Effective biliary decompression was achieved in all patients initially. No acute stent-related complications occurred. The 30-day mortality rate was 20%. During follow-up, 11 stent occlusions occurred; therefore, the occlusion rate was 37%. The patency rates after 1, 3, 6, and 12 months were 96%, 69%, 47%, and 31%, respectively. Tumor growth through the stent covering that was proven both histologically and by biopsy observed in two patients, causing stent occlusion in one of them. Other reasons for stent occlusion were distal tumor ingrowth (n = 1) and biopsy-proven granulation tissue inside the stent (n = 2). Otherwise, the reasons for stent occlusion remained unclear. CONCLUSION: This prototype of a covered stent did not provide better results than did conventional uncovered stents in patients with malignant biliary obstruction. The covering did not effectively prevent tumor ingrowth in at least two patients. The stent also seems prone to premature occlusion.

Aged↗

PubMed1993

Replacement of the os trapezium by polyurethane implants.

Twenty-five patients with arthrosis of the first carpometacarpal joint had the os trapezium replaced by a polyurethane implant (Tecoflex), and the results were evaluated after three years (range 28-47 months). There were three failures in which the implants had been removed because of dislocation with pain. The clinical results in the remaining 22 cases in terms of relief of pain and thumb function were comparable with previous series of silicone implants. Radiographic examination showed no signs of bone resorption or other unfavourable tissue reactions around the implants, but subluxation of the implants was seen in half of the cases. Implant subluxation might be caused by poor design of the implant or the limited amount of fibrous foreign-body reaction around the polyurethane material that resulted in less firm encapsulation than occurred around silicone implants.

Adult↗

PubMed1984

The use of flexible polyurethane foam in orthotics.

The casting of flexible polyurethane foam into a wide range of customised shapes has been found to offer a relatively straightforward solution to a number of problems associated with providing support for the physically handicapped. This note describes the techniques used for the production of such supports and reports on clinical experience of their use. A suitably prepared plaster cast of the patient, obtained in the usual way via vacuum consolidation of polystyrene beads, forms the lower surface of a wooden moulding box. Suitable quantities of the two chemicals, an isocyanate and a polyol, are then thoroughly and rapidly mixed together before being poured into the moulding box over which a weighted lid is placed to contain the foam and to improve its consistency. After removal, the finished product can then be trimmed and if necessary covered with fire-retardant leathercloth. To date polyurethane foam mouldings have been used with considerable success as seat cushions, seat backs and as spinal body supports which allow a patient to be nursed prone and supine following spinal fusion.

Construction Materials↗

PubMed1990

Biologically inert synthetic dural substitutes. Appraisal of a medical-grade aliphatic polyurethane and a polysiloxane-carbonate block copolymer.

Two types of artificial membranes, a medical-grade aliphatic polyurethane and a polysiloxane-carbonate block copolymer, were tested as substitutes for dura in 24 and 12 rabbits, respectively. The films were placed either epidurally, subdurally, or as dural grafts in equal subgroups of animals. The postoperative course was uneventful with no manifestations of convulsive disorder or cerebrospinal fluid leak. The animals were sacrificed 3, 6, or 9 months after implantation of the artificial membranes. Both types of artificial membranes were easily removed from the underlying nervous and the other surrounding tissues. The histological examination failed to reveal adhesions, neomembrane formations, or any type of foreign body reactions to the polyurethane film. The implantation of the polysiloxane-carbonate film caused no reaction when it was applied epidurally. As a dural graft, the polysiloxane-carbonate copolymer induced the formation of a thin neomembrane of one to two layers of fibroblasts which formed a watertight seal of the dural defect. A similar thin neomembrane was found to encase this artificial membrane in the group of animals in which it was implanted subdurally. There was no foreign body reaction to the polysiloxane-carbonate film. The authors conclude that these materials hold promise as dural substitutes or in the prevention of spinal dural scarring, and should be evaluated clinically.

Animals↗

PubMed2004

Phase variation of biofilm formation in Staphylococcus aureus by IS 256 insertion and its impact on the capacity adhering to polyurethane surface.

While ica gene of Staphylococcus epidermidis is known to undergo phase variation by insertion of IS256, the phenomenon in Staphylococcus aureus has not been evaluated. Six biofilm-positive strains were tested for the presence of biofilm-negative phase-variant strains by Congo red agar test. For potential phase-variant strains, pulsed-field gel electrophoresis was done to exclude the possibility of contamination. To investigate the mechanism of the biofilm-negative phase variation, PCR for each ica genes were done. Changes of ica genes detected by PCR were confirmed by southern hybridization, and their nucleotides were analyzed by DNA sequencing. Influence of ica genes and biofilm formation on capacity for adherence to biomedical material was evaluated by comparing the ability of adhering to polyurethane surface among a biofilm-negative phase-variant strain and its parent strain. A biofilm-negative phase-variant S. aureus strain was detected from 6 strains tested. icaC gene of the phase-variant strain was found to be inactivated by insertion of additional gene segment, IS256. The biofilm-negative phase-variant strain showed lower adhering capacity to polyurethane than its parent strain. This study shows that phase variation of ica gene occurs in S. aureus by insertion of IS256 also, and this biofilm-negative phase variation reduces adhering capacity of the bacteria.

Bacterial Adhesion↗

PubMed1980

Mutagenic action of isocyanates used in the production of polyurethanes.

Isocyanates used in the production of polyurethanes were investigated for mutagenic action in Salmonella typhimurium. These investigations showed that the most commonly used isocyanates, toluene diisocyanate (TDI) and 4,4'-methylene-diphenylisocyanate (MDI), are mutagenic. This effect can be ascribed to the amine analogues formed during the hydrolysis of isocyanates: TDI is mutagenic in TA 1538 and TA 98 after metabolic activation. This finding agrees with the results obtained with the amine analogue 2,4-toluenediamine. MDI, like the amine analogue 4,4'-methylenedianiline, is mutagenic in TA 100 after metabolic activation by rat liver enzymes (S-9 mix). A prepolymerized polyisocyanate of the MDI type is also mutagenic in assays using TA 100 and S-9 mix. It is concluded that isocyanates are potentially mutagenic and carcinogenic to man. In view of their widespread use in the work environment and in light of the high production figures for polyurethanes in industrialized countries, isocyanates must be considered to represent a serious health hazard.

Cyanates↗

PubMed1999

Retrospective report on the effectiveness of a polyurethane football helmet cover on the repeated occurrence of cerebral concussions.

This report reviews the literature and unpublished data and presents survey results related to the use of a polyurethane football helmet cover. Two hundred forty-five individuals, identified by the helmet manufacturer as having purchased at least one device, were sent a survey after the 1992, 1993, and 1994 football seasons; 155 (63.3%) of the surveys were returned. The questionnaire, designed to be completed by the athlete, required a detailed history of concussions occurring both prior to and during the period the device was used. Individuals used the device as a result of having incurred at least one concussion. Rates of concussion reoccurrence while the device was worn were grouped by the number of previous concussions (1, 2, 3, or 4+) that occurred over a 4year period prior to use of the device. The rate of concussion reoccurrence was 2.4%, 7.3%, 15.8%, and 33.3%, respectively, over a 4-year period. The range appeared to reflect a parallel relationship between pre- and post-device concussion experiences: the more concussions experienced prior to adopting the device, the higher the rate of concussion reoccurrence while using the device. The natural history of repeated occurrences of concussive events may not be affected by the use of a polyurethane football helmet cover. We suggest that such a device not be routinely used prophylactically, but instead be reserved for individuals with 1 to 2 prior concussion injuries. However, at this time, we neither recommend nor discommend the device.

Adolescent↗

PubMed1995

Polyurethane paranoia flexible friend or deadly foe?

One of the most versatile of all materials used in medical devices has been under a cloud of suspicion for a few years, because of concerns about degradability and carcinogenicity. There is considerable confusion about the exact nature of polyurethanes and the extent of the problem. This article attempts to explain the essentials of polyurethane chemistry and put these concerns into perspective.

Animals↗

PubMed1991

Polyurethanes in medical devices.

Because of their biocompatible qualities, polyurethanes have found many uses in the medical device field. This article describes several of the better-known polyurethanes and discusses their suitability for use in medical applications such as artificial heart systems, catheters, mammary implants, semiocclusive dressings, and drug delivery systems. The adoption and use of these materials by the medical community is likely to increase as new formulations are developed.

Biocompatible Materials↗

PubMedDate not supplied

Diisocyanates in polyurethane plastics applications.

Diisocyanates are a group of low molecular weight aromatic and aliphatic compounds, widely used in the manufacture of polyurethanes. The most commonly used of these compounds are toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), and hexamethylene diisocyanate (HDI). This article presents a brief summary of the use of diisocyanates in the manufacture of polyurethane products and a review of the epidemiology, medical surveillance, and clinical diagnosis of respiratory and dermal effects of diisocyanates, with emphasis on diisocyanate asthma.

Humans↗

PubMed1999

Exposure to MDI during the process of insulating buildings with sprayed polyurethane foam.

Buildings are often insulated with sprayed-in-place polyurethane foam in spite of the fact that few studies have been carried out on exposure levels to isocyanates during the spraying process. This paper is meant to provide new data on personal exposure to methylene-bis (4-phenylisocyanate) (MDI) while dwellings and office buildings are being insulated with polyurethane foam. An impinger using a 1-(2-methoxyphenyl)piperazine toluene solution as absorbent was used to take personal samples for the sprayer and helper during indoor and outdoor applications. The analytical results show that the levels of exposure were significant, especially for the sprayer, with values of up to 0.077 mg m-3 and 0.400 mg m-3 during outdoor and indoor applications, respectively. The helper's exposure was always lower.

Aerosols↗

PubMed2000

Comparative In vitro evaluation of two different preparations of small diameter polyurethane vascular grafts.

Polyurethane (PU) frequently has been used to manufacture small diameter vascular grafts due to its good bicompatibility. In this study, sponge PU small diameter vascular grafts were fabricated from Pellethane 2103, as well as a self-synthesized PU, by utilization of a salt casting technique and by varying the salt/polymer ratios. Two types were made; one of them had a thin solid layer on the outer surface. The inner surface was identical and was coated with gelatin crosslinked by epoxide. Tensile properties, compliance, platelet activation, and endothelial cell attachment were evaluated in vitro. It was found that for the grafts with an outer nonporous coating, compliance could not be estimated from modulus due to anisotropy. The most compliance-matched grafts were made of self-synthesized polyurethane with a salt/polymer ratio 4 to 8 or Pellethane with a ratio 6 to 8 without the outer nonporous coating. The former had better elongation. Self-synthesized PU had lower platelet adhesion as well as more endothelial attachment than Pellethane. Porosity activated platelets strongly and reduced endothelial adhesion unless the surface was modified by the crosslinked gelatin layer. It was concluded that PU synthesized in our lab with a salt/polymer ratio of at least 4 and coated with epoxy crosslinked gelatin was a better substrate for preparation of small diameter vascular grafts.

Animals↗

PubMed1975

Carcinogenesis from polyurethans.

Seventeen polyurethans, containing various substituent groups, and a polyethylene were implanted i.p. in groups of male black Bethesda rats and were evaluated for carcinogenesis over a 2-year period. Thirteen of the polyurethans and the polyethylene were similarly studied in females. Tumor development in these animals was expressed in terms of the incidence in the at-risk population, and the tumorigenic latent period was approximated for each sample. Twenty months after implantation, the relative tumorigenicity (area under the corrected cumulative tumor mortality versus time curve) in the males ranged from 0 (for the unimplanted controls) to 6.18 (for Y-238); for female rats this range was 0.29 (for unimplanted controls) to 5.72 (for Y-238). Estimated latent periods in the males ranged from 5 months (for Y-304) to 16 months (for Y-303), and 22.5 months for the unimplanted controls; for the females, the range was from 9 months (for Y-290) to 13.5 months (for Y-217), and 14 months for the unimplanted controls. The relative tumorigenicity of each sample was also compared to its in vitro activation energy for thermal decomposition. These data are discussed in terms of solid-state versus chemical carcinogenesis.

Animals↗

PubMed2001

Polyurethane foam based biofilter media for toluene removal.

Polyurethane foam medium was manufactured and analyzed to determine its suitability as a solid support medium for use in gas-phase biofilters. Physical and chemical studies were conducted to determine the medium's characteristics. The medium's ability to support an active biofilm capable of degrading volatile organic compounds was assessed using a laboratory scale biofilter fed a model waste stream containing toluene for more than 250 days with empty bed residence times (EBRTs) ranging from two to four minutes. Results are presented that show how a polyurethane foam medium with high porosity, suitable pore size, low density, and an ability to sorb water was able to remove over 99% of the influent toluene when fed at a concentration of 200 ppm. An operating strategy is described which effectively prevented two problems common to conventionally operated biofilter systems: nutrient limitations and biosolid accumulation.

Air Pollutants↗

PubMed2001

The polyurethane-covered mammary prosthesis: facts and fiction (II): a look back and a "peek" ahead.

The senior author believes that there is a niche for polyurethane-covered devices in the new millennium if they in fact become available. During the span of this author's practice, he has never been able to match the number and quality of superior results exemplified by these patients when using other devices. Women seeking reconstruction after mastectomy or aesthetic improvement will be well served if the polyurethane-covered device once again becomes one of the choices of mammary prostheses available to them, in this author's opinion.

Breast Implants↗

PubMed2002

[Replacement of bone defects with a polyurethane composition with hydroxyapatite high-filling ].

There have been obtained high-filling polyurethane compositions with hydroxyapatite. Compositions with hydroxyapatite and immunomodulator in the polyurethane base acquire better adhesiveness and improved strength characteristics as evidenced by physical-and-clinical studies made. Modal operations are developed in test animals on bone defects replacing that carry a high mechanical load. Histological studies showed that polyuretane-base high-filling polymeric compositions replace the loss of bone fully, stimulate the processes of bone formation, with no negative responses of the osseous tissue noted.

Animals↗