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PubMed2004

The effect of bone cement particles on the friction of polyethylene and polyurethane knee bearings.

Compliant layer knee joints have been considered for use in an attempt to increase the serviceable life of artificial joints. If designed correctly, these joints should operate within the full-fluid film lubrication regime. However, adverse tribological conditions, such as the presence of bone and bone cement particles, may breach the fluid film and cause surface wear. The frictional behaviour of both polyurethane (PU) and conventional polyethylene (PE) tibial components against a metallic femoral component was therefore assessed when bone cement particles were introduced into the lubricant. The bone cement particles caused a large increase in the frictional torque of both the PE and PU bearings; however, the friction produced by the PU bearings was still considerably lower than that produced by the PE bearings. The volume of bone cement particles between each of the bearings and the resultant frictional torque both decreased over time. This occurred more quickly with the PE bearings but greater damage was caused to the surface of the PE bearings than the PU components.

Biocompatible Materials↗

PubMed2003

Silk fibroin-coated three-dimensional polyurethane scaffolds for tissue engineering: interactions with normal human fibroblasts.

Silk fibroin (SF)-based or -coated biomaterials hold structural and surface properties that render them suitable for biomedical applications. In this work, we investigated the behavior of four strains of normal human adult fibroblasts (HAFs) seeded onto polyurethane foam, uncoated (PUF) or SF coated (PUF/SF). HAF adhesion within 3 h to PUF/SF was 2-fold that of adhesion to PUF. After 30 days of incubation in vitro, 37% more HAFs had grown on PUF/SF than on PUF. Taking 10(5) cells as a basis for comparisons, HAFs on PUF/SF exhibited initially higher glucose consumption rates, but persistently lower glutamine uptake rates than on PUF, whereas the rates of lactate and interleukin 6 release and of extracellular assembly of type I collagen fibers were alike on either substrate. Moreover, HAFs on both PUF/SF and PUF never secreted any ELISA-assayable amounts of interleukin 1beta, tumor necrosis factor alpha, and transforming growth factor beta(1). Hence, PUF/SF scaffolds embody a novel class of biomaterials favoring the adhesion, proliferation, and performance of specific metabolic tasks by HAFs without eliciting any concurrent secretion of the chief proinflammatory cytokines.

Adaptation, Physiological↗

PubMed2004

Assessment of encrustations on polyurethane ureteral stents.

PURPOSE: To determine the composition and the extent of crystalline (and other) encrustation on ureteral catheters inserted under sterile conditions in stone formers, in comparison with catheters of the same type inserted in nonstone formers for the same time but for different clinical reasons. MATERIALS AND METHODS: Forty consecutive self-retained polyurethane pigtail ureteral catheters removed by cystoscopy between November 2000 and February 2002 were studied, 30 from stone formers and 10 from patients without stone histories. The mean dwelling time was 55 days for the stone formers and 79 days for the other patients. The encrustations were collected and analyzed with Fourier-transform infrared spectroscopy, powder X-ray diffraction, or both. The stones from nine of the patients were also subjected to the same spectroscopic analysis. Representative sections of the catheters were investigated by scanning electron microscopy and energy-dispersive X-ray analysis. RESULTS: The most common encrustation in stone formers was calcium oxalate monohydrate. In patients without stones, deposits of organic compounds were found consistently. The mean mass of encrustation of stone formers was larger (71.05 mg) than that of patients without stones (1 mg). CONCLUSIONS: Calcium oxalate is the predominant type of encrustation on ureteral catheters in stone formers. Prevention of heavy encrustation should be directed to therapeutic measures concerning calcium oxalate lithiasis and development of new materials by the medical industry that are less prone to encrustation.

Calcinosis↗

PubMedDate not supplied

Composite articular cartilage engineered on a chondrocyte-seeded aliphatic polyurethane sponge.

To circumvent the reconstructive disadvantages inherent in resorbable polyglycolic acid (PGA)/polylactic acid (PLA) used in cartilage engineering, a nonresorbable, and nonreactive polyurethane sponge (Tecoflex sponge, TS) was studied as both a cell delivery device and as an internal support scaffolding. The in vitro viability and proliferation of porcine articular chondrocytes (PACs) in TS, and the in vivo generation of new articular cartilage and long-term resorption, were examined. The initial cell attachment rate was 40%, and cell density increased more than 5-fold after 12 days of culture in vitro. PAC-loaded TS blocks were implanted into nude mice, became opalescent, and resembled native cartilage at weeks 12 and 24 postimplantation. The mass and volume of newly formed cartilage were not significantly different at week 24 from samples harvested at week 6 or week 12. Safranin O-fast green staining revealed that the specimens from cell-loaded TS groups at week 12 and week 24 consisted of mature cartilage. Collagen typing revealed that type II collagen was present in all groups of tissue-engineered cartilage. In conclusion, the implantation of PAC-TS resulted in composite tissue-engineered articular cartilage with TS as an internal support. Long-term observation (24 weeks) of mass and volume showed no evidence of resorption.

Animals↗

PubMedDate not supplied

Fibrin-polyurethane composites for articular cartilage tissue engineering: a preliminary analysis.

In this study we investigated the use of a fibrin hydrogel to improve the potential of a polyurethane (PU) scaffold-based system for articular cartilage tissue engineering. PU-only ("no-fibrin") and PU-fibrin ("fibrin") composites were cultured for up to 28 days and analyzed for DNA content, glycosaminoglycan (GAG) content, type II collagen content, GAG release, and gene expression of aggrecan, collagen I, and collagen II. The use of fibrin allowed for higher viable cell-seeding efficiency (10% higher DNA content on day 2 in fibrin versus no-fibrin composites) and more even cell distribution on seeding, a more than 3-fold increase in the percentage of newly synthesized GAG retained in the constructs, and 2- to 6-fold higher levels of type II collagen and aggrecan gene expression through day 14. Addition of aprotinin to the medium inhibited fibrin degradation, most noticeably in the center of the constructs, but had little effect on biochemical composition or gene expression. Short-term mechanical compression (0-10% sinusoidal strain at 0.1 Hz for 1 h, applied twice daily for 3 days) doubled the rate of GAG release from the constructs, but had little effect on gene expression, regardless of the presence of fibrin. Although further work is needed to optimize this system, the addition of fibrin hydrogel to encapsulate cells in the stiff, macroporous PU scaffold is a step forward in our approach to articular cartilage tissue engineering.

Aggrecans↗

PubMed2006

Biodegradable elastomeric polyurethane membranes as chondrocyte carriers for cartilage repair.

Autologous chondrocyte implantation in combination with an autologous periosteal patch has become a clinically accepted procedure for the treatment of articular cartilage defects. The use of periosteum has, however, several drawbacks. We have been able to fabricate thin elastomeric biodegradable polyurethane (PU) membranes that may possibly have an application as a tissue-engineered substitute for the periosteal patch. Three types of membranes varying in pore size and surface texture were used as substrates for bovine chondrocytes in culture. The membranes, marked as P-I, P-II, and P-R, had average pore sizes of 10 to 20 microm, 40 to 60 microm, and less than 5 microm, respectively. A poly(L/DL-lactide) 80/ 20% micro-porous membrane (PLA) with an average pore size in the range of 10 to 70 microm was used as a control. There was no difference in the cell proliferation profile among the 4 membranes. In terms of proteoglycan and collagen production, P-I, P-R, and PLA performed similarly to one another. The rate of matrix production appears to be greater in the PU membranes than in the PLA membrane in the first 10 days, although by day 30, the PLA membrane had caught up. In all comparisons, the performance of P-II lagged behind those of the other materials. In conclusion, this preliminary study supports the potential use of this novel group of PUs as a periosteal flap substitute or perhaps as a chondrocyte carrier for matrix-assisted chondrocyte implantation and related techniques. Further studies will be necessary to better define their role in clinical applications for cartilage repair.

Absorbable Implants↗

PubMed2004

A survey of airborne isocyanate exposure in 13 Swedish polyurethane industries.

Exposure to isocyanates can be harmful to workers by causing different disorders of the airways. The main objectives of this study were to survey the personal 8 h time-weighted average exposure to isocyanates at 13 Swedish plants that handled either polyurethane, diisocyanates or both, including four types of manufacturing processes: moulding, continuous foaming, flame lamination and low or no heating processes. A total of 223 air samples were collected for 111 workers with personal air monitoring using a dry filter method with 1-(2-methoxyphenyl)piperazine (2MP) as derivatization reagent. A further 272 stationary samples were collected, using the 2MP method, a modified 2MP method and an impinger method using dibutylamine in toluene. With the applied strategy, a large number of workers were monitored and four industrial environments were compared regarding the isocyanate exposure. All workers were found to be exposed to isocyanates in the range 0.004-5.2 p.p.b. On average, the personal exposure levels in the different types of manufacturing processes were, in decreasing order: continuous foaming > flame lamination > moulding >> low or no heating processes. However, there were variations in exposure levels in plants with similar processes and also between different shifts performing the same tasks. Isocyanic acid, which could not be sampled by the 2MP method used for personal monitoring, was found by short-term stationary monitoring in levels up to 38 p.p.b. in the flame lamination plants.

Air Pollutants, Occupational↗

PubMedDate not supplied

Analysis of a carcinogen, 4,4'-methylenedianiline, from thermosetting polyurethane during sterilization.

Polyurethane (PU) is widely used in medical devices such as potting material in artificial dialysis devices, plasma separators, etc. Gamma-ray irradiation is frequently used for the sterilization of such devices. This paper reports that a carcinogen, 4,4'-methylenedianiline (MDA, p,p'-diaminodiphenylmethane), is produced from medical thermosetting PU by gamma-ray irradiation. Gamma-ray irradiated PU was immersed in methanol or equine serum. The serum was treated with a mixture of 5N HCIO4:acetonitrile (1:10) in order to deproteinate and recover MDA. It was found that MDA is formed from thermosetting PU at around a few ppm in the original sample. The production of MDA increased with increasing irradiation dose. The MDA amount formed was related to the irradiation dose by a second order equation. Results of methanol and serum extraction were similar. Pressurized steam (autoclave) sterilization in place of gamma-ray sterilization was also examined. MDA production was not found in autoclave sterilization procedures. Gel permeation chromatography (GPC) of methanol or N,N-dimethylformamide (DMF) extract of irradiated PU showed that the PU oligomers eluted. Time course of methanol extract of irradiated PU was detected at 245.5 nm. This showed an exponential decline regardless of doses of irradiation.

Aniline Compounds↗

PubMed2001

Biological monitoring of workers exposed to dimethylformamide in a textile polyurethane unit.

Dimethylformamide (DMF) is a universal solvent noted for its solubility in both aqueous and lipid media. It is hepatotoxic, and there are concerns about its carcinogenicity. Our objective was to determine the correlation between air monitoring measurements and biological measurements of a suitable metabolite of DMF in a cohort of operatives in a polyurethane production unit. This was done with a view to assessing how much the inhalation route contributed to total DMF exposure, mainly for control purposes. We investigated the relationship between personal air sample measurements of DMF and biological measurements of N-methylformamide (NMF) in nine adult subjects, recruited across the shifts, with varying levels of exposure to DMF. Personal exposure monitoring was carried out with a low-flow-rate Model 222-4 SKC pump, while post-shift urine samples were obtained for further analysis. Operatives were asked to abstain from consuming alcohol for 24 h before the designated shift, as advised by the laboratory responsible for the analysis of urine samples. We found a very strong statistical association between air sample measurements of DMF and NMF in the urine of the sample population (R(2) = 0.95, P < 0.0001). This study suggests that airborne exposure contributes significantly to elevated levels of NMF and, therefore, indicates that efforts should be concentrated on engineering controls in reducing workplace DMF exposure.

Adult↗

PubMed1984

Reconstruction of breasts following mastectomy with polyurethane-covered, gel-filled prostheses.

This article describes a simple, one-stage procedure to reconstruct breasts following radical and subcutaneous mastectomy by using subcutaneous placement of Natural-Y prostheses (polyurethane-covered, gel-filled implants with an internal Y-shaped septum). Breast reconstruction after mastectomy or immediately following subcutaneous mastectomy was performed in 36 patients using 62 Natural-Y prostheses. All patients still had implants in place six months to five years later. Neither spherical capsular contractures, infection, nor skin necrosis developed around any implants. Transfer of pedicle flaps was not required in any patient and the reconstructive procedures resulted in minimal scarring. Wrinkling of skin and a palpable implant edge in the superior quadrant were noticeable in some breast reconstructions following subcutaneous mastectomy but rarely in breasts reconstructed following mastectomy because the taut skin conformed to the implant.

Breast↗

PubMed1988

Breast reconstruction with a subcutaneous tissue expander followed with a polyurethane-covered silicone breast implant.

We have reexamined the subcutaneous route of reconstruction of the breast following mastectomy. For either delayed or immediate reconstruction of the breast, we have used a subcutaneously placed Radovan tissue expander, followed by expansion of the skin flap, then capsulotomy and insertion of the polyurethane-coated implant. The results of these procedures are presented after follow-up periods ranging from one and one-half to three years, with more than satisfactory results.

Adult↗

PubMed1990

Polyurethane nipple prosthesis.

Long-term nipple projection remains the elusive ingredient for measuring the success of a nipple reconstruction. Augmentation of this projection without sacrifice of autogenous donor tissues may be achieved using a polyurethane-coated silicone gel implant affectionately and descriptively called the "gumdrop" nipple. Two patients who agreed to implantation with this device have each been observed over a one-year period with no loss of projection. The role of an internal nipple prosthesis, although perhaps of some value as a salvage procedure, appears to offer few advantages over other accepted methods of reconstruction that do not use any foreign body.

Adult↗

PubMed1991

Transparent polyurethane (Omiderm) dressing for free flaps.

A transparent polyurethane dressing (Omiderm) for free flaps is presented. Considering the importance of reliable flap monitoring postoperatively, this synthetic membrane allows for constant ability to observe the flap, assess the capillary filling, and detect the blood flow with an ultrasound Doppler device.

Bandages↗

PubMed1995

Synovial metaplasia of a periprosthetic capsule surrounding a polyurethane foam breast prosthesis.

A 43-year-old woman underwent two-stage bilateral reconstruction mammoplasty using silicone-filled, polyurethane foam-covered breast implants. The permanent implants were later removed. The periprosthetic capsule demonstrated synovial metaplasia by light and electron microscopy. Synovial metaplasia is believed to be induced by the physical and chemical characteristics of the prostheses and may have important clinical implications in reducing capsular contracture and increasing host acceptance of implantable biomaterials.

Adult↗

PubMedDate not supplied

New polyurethane valves in new soft artificial hearts.

This article describes new bistable valves, and introduces a new soft heart that is easy to implant. Earlier, five polyurethane (PU) valves were implanted in the mitral position in sheep. All five survived for 1 year or more, and the valves, although calcified, were intact. Since the opening resistance was somewhat high, valves that are bistable were developed, which means they may be open or closed. These valves have lower opening resistance, and regurgitation is similar to that of mechanical valves. Eight calves have been implanted with a new, soft total artificial heart (TAH). Seven had bistable leaflet valves; the eighth had mechanical (Bicer) valves in the inflow position. Four of the calves were sacrificed after 22 to 43 days. At autopsy, the number of thromboemboli found, particularly in the kidneys, was low compared with previous experiments. None of these animals received anticoagulants other than the heparin given during heart/lung bypass.

Animals↗

PubMedDate not supplied

Albumin immobilized polyurethane and its blood compatibility.

Surface pretreatment with albumin on a blood contacting material inhibits platelet adhesion, activation, and subsequent thrombus formation. Although adsorbed albumin improves blood compatibility, rapid desorption occurs when this surface is exposed to circulating blood. In this study, human serum albumin was immobilized on a polyurethane (PU) surface to investigate its blood compatibility and extended effects on a blood-material interface. The PU surface was treated with hexamethylene diisocyanate (HMDI), and the PU-HMDI was further grafted with albumin to produce an albumin immobilized PU surface (PU-albumin). The PU-albumin surface was characterized by attenuated total reflection infrared electron spectroscopy for chemical analysis, scanning electron microscopy, and dynamic contact angle. Blood compatibility was evaluated by in vitro protein adsorption, platelet adhesion, and occlusion time in an ex vivo rabbit arterio-arterial shunt. Immobilization of albumin was confirmed by the disappearance of the -NCO peak observed at 2,250 cm-1 on the PU-HMDI surface by infrared spectroscopy and the existence of sulfur atomic percent by electron spectroscopy for chemical analysis. The concentration of PU-albumin was approximately 5.8 micrograms/cm2. The PU-albumin also showed a slight increase in hydrophilicity on the Wilhelmy plate method, and there was less fibrinogen adsorption than a PU control. In addition, PU-albumin had less platelet adhesion, platelet activation, and thrombogenicity. The ex vivo occlusion time of untreated PU was 50 min, that of PU-albumin was extended to 150 min, indicating that a PU-albumin surface has better blood compatibility than PU alone.

Adsorption↗

PubMedDate not supplied

Experimental study of bioactive polyurethane sponge as an artificial trachea.

An artificial trachea that has tissue reconstructive activity and elasticity that matches a biologic trachea was fabricated using a polyurethane sponge (PS). The inner surfaces of the PS were modified by immobilizing collagen, fibronectin, RGD peptide, a coating of collagen, and apatite. Two PS pore sizes were prepared, 150 to 350 microns (small pore) and 350 to 710 microns (large pore). When they were implanted in the subcutaneous tissue of rats, study of the implantation showed severe inflammatory cell infiltration with the treated PS, especially with collagen and collagen coating. Infiltration and maturity of fibroblasts inside the PS were noted with fibronectin. Infiltration of inflammatory cells and fibroblasts was noted with small pore PS compared with large pore PS. Partial tracheal defects were patched with PS. Better epithelization of PS patches was observed with fibronectin and apatite compared with the others. The artificial trachea made of PS was transplanted into the tracheas of dogs. No separation of the anastomosis and tissue reconstruction of the artificial trachea wall were observed; however, sputum absorption and tracheal granulation were seen.

Amino Acid Sequence↗

PubMedDate not supplied

In vitro studies of immobilized heparin and sulfonated polyurethane using epifluorescent video microscopy.

In situ surface modification techniques to improve the blood compatibility of blood contacting surfaces of medical devices have been developed by the authors. The techniques include heparin immobilization and sulfonated polymer grafting onto a polyurethane (PU) surface by using either ozone oxidation or photo reaction. These modified PUs were evaluated using an epifluorescent video microscope combined with a parallel plate flow cell. The epifluorescent video microscope system measured the amount of platelet coverage on the PU surfaces using whole human blood containing mepacrine labeled platelets perfused at a wall shear rate of 100 sec-1 for 20 min. Platelet activation and complement activation were also measured. Both immobilized heparin and sulfonated PUs showed significantly lower levels of platelet adhesion than the control PU. The platelet activation levels of these modified PUs also correspond to the results of the platelet adhesion. As for complement activation, heparin the immobilized surface showed the least complement activation, while sulfonated PU and the control PU showed higher levels of complement activation. In situ surface modification techniques, which use either ozone oxidation or photo reaction, are useful in a variety of medical devices even of a complex design, such as membrane oxygenators or artificial hearts.

Allylamine↗