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PubMed2001

Interaction of blood components with heparin-immobilized polyurethanes prepared by plasma glow discharge.

The blood compatibility of poly(ethylene oxide) (PEO)-grafted and heparin (Hep) immobilized polyurethanes was investigated using in vitro plasma recalcification time (PRT), activated partial thromboplastin time (APTT), platelet adhesion and activation, and peripheral blood mononuclear cell (PBMC) adhesion and activation. In the experiment with plasma proteins, the PRT of the polyurethane (PU) surface was prolonged by PEO grafting and further prolonged by heparin immobilization. The APTT was prolonged on PU-Hep, suggesting the binding of immobilized heparin to antithrombin III. The percentage of platelet adhesion on PU was not much different from that on acrylic acid- and PEO-grafted PUs (PU-C, PU-6, PU-33), yet was substantially decreased by heparin immobilization (PU-6-Hep, PU-33-Hep). The release of serotonin from adhering platelets was slightly suppressed on PEO-grafted PUs yet significantly suppressed on heparin-immobilized PUs. In the PBMC experiments, the adhesion and activation of the cells were significantly suppressed on heparin-immobilized PUs, and the amount of interleukin-6 (IL-6) released from PBMCs stimulated with surface-modified PUs decreased with a decrease in PBMC adhesion.

Biocompatible Materials↗

PubMed1990

The in vivo auto-oxidation of polyether polyurethane by metal ions.

The first large scale use of polyether polyurethane elastomers in long term human implants was as insulation for cardiac and neurologic pacing leads. While the performance of these polymers has generally been very good over a 14-year period, several failure mechanisms have been discovered that involve interactions between the devices, materials and the body. One of these is auto-oxidation of soft segment ether through the intermediate action of certain transition metal ions, derived from conductor wires by corrosion processes. Biologically produced oxidants appear to be an accelerating factor. In this study, Pellethane 2363-80A tubing containing conductor coils or mandrels of various metals or controls were implanted in rabbits. Explants were analyzed as a function of implant time by optical and scanning electron microscopy, electron dispersive analysis by X-ray, stress-strain, FTIR, GPC and AA spectrophotometry. Only cobalt produced bulk oxidative degradation while surface damage was found in the presence of cobalt bearing alloys. No evidence of significant auto-oxidation was found in the presence of silver, nickel, chromium, molybdenum, iron, titanium, platinum, 304 stainless steel, glass or empty tubing. The combination of polyether polyurethane and metals (especially those containing cobalt) in an implantable device must be carefully evaluated for biostability prior to human use.

Biocompatible Materials↗

PubMed1993

Effect of polyurethane surface chemistry on its lipid sorption behavior.

The relationships among surface, bulk properties and lipid sorption behaviors of segmented polyurethanes (SPUs) with various polyol soft segments were investigated. The polyols used in this study were poly(ethylene oxide) (PEO), poly(tetramethylene oxide) (PTMO), and poly(dimethylsiloxane) (PDMS). The hard segment of these segmented polyurethanes was composed of 4,4'-diphenylmethane diisocyanate and 1,4-butanediol, present at 50 wt%. X-ray photoelectron spectroscopic (XPS) and dynamic contact angle measurements were carried out in order to analyze the surface chemical structure in the air- and water-equilibrated states. XPS revealed that in the air-equilibrated state, lower surface free energy components were enriched at the air-solid interface, whereas in the water-equilibrated state, higher surface free energy components were enriched at the water-solid interface. The change in environment from air to water induced the surface reorganization in order to minimize interfacial free energy. Lipid sorption behaviors of SPUs were investigated by means of infrared spectroscopy. Even after extensive rinsing of the surface, the amount of lipid present on the SPU surface was more than that calculated on the assumption that a monolayer covers the SPU surface. Therefore, the lipid was not only adsorbed on the surface of SPU but absorbed into SPU. The SPU with hydrophilic PEO sorbed larger amount of phospholipid compared with that with hydrophobic polyol such as PTMO and PDMS. Also, the competitive sorption behaviors of phospholipid and cholesterol from their mixed liposome solution were studied. The ratio of sorbed cholesterol to phospholipid increased with an increase in surface hydrophobicity owing to the hydrophobic nature of cholesterol.

Absorption↗

PubMed1996

Preparation and evaluation of polyurethane surfaces containing immobilized plasminogen.

Plasminogen has been immobilized onto a segmented polyurethane containing amino groups, using glutaraldehyde as coupling agent. It was also aspecifically adsorbed, for sake of comparison, onto polyurethane films containing different functional groups and, in particular, epsilon-amino caproic acid and lysine residues. The differently immobilized plasminogen has been converted to plasmin by activation with urokinase, and the percentage of active plasmin for the various polymer films was determined using a tripeptide (S-2251) as a synthetic substrate. The biological behaviour of the differently treated polymer films has been evaluated in vitro by measurements of partial thromboplastin time (PTT) and platelet adhesion.

Anticoagulants↗

PubMed1997

Hemocompatibility studies of surface-treated polyurethane-based chronic indwelling catheters.

The objectives of this research were to evaluate and compare the interactions of several polyurethane-based central venous catheter materials with blood. Specifically, measurements of fibrinogen adsorption, platelet adhesion, kallikrein generation, and fibrinopeptide A (FPA) release were performed. The catheter materials examined in this study included: platinum-cured, 50 shore A durometer, barium sulfate-filled, silicone (SI); Tecoflex EG85A-B20 polyurethane (PU); PU catheters whose outer surface had been impregnated with ion beam-deposited silver atoms (AgI and AgII); PU catheters coated with a hydrophilic, polyacrylic acid polymer (UC); PU catheters coated with an air-cured PTFE emulsion (CS); and PU catheters coated with an aminofunctional dimethylsiloxane copolymer (JG). The time course of fibrinogen adsorption from plasma to the SI, JG, PU, and CS materials was similar, with CS exhibiting the least amount of adsorbed fibrinogen after 1 h (65 +/- 4.7 ng cm-2) and PU the greatest (144 +/- 16.5 ng cm-2). After 90 min of contact, AgI and AgII exhibited the greatest number of adherent platelets, levels that were approximately two to three times higher than those on the other catheter materials. With the exception of UC and PU, which caused kallikrein generation levels approximately half that of the positive (glass) control, little kallikrein formation was observed for any of the materials relative to the negative control. Finally, FPA generation was greatest using the SI, CS, and PU materials, with the latter causing the production of almost four times the amount of FPA as the negative control. This preliminary assessment of the hemocompatibility of the various catheters suggests that the surface treatments did not adversely affect their interactions with blood components; further investigations of these materials are therefore warranted in order to completely characterize their behavior prior to use in clinical situations.

Adsorption↗

PubMed1998

Formation of a spherical multicellular aggregate (spheroid) of animal cells in the pores of polyurethane foam as a cell culture substratum and its application to a hybrid artificial liver.

Monkey kidney cells (Vero), human embryonic kidney cells (293), human liver cells (PLC/PRF/5), and primary rat, dog, and porcine hepatocytes formed spherical multicellular aggregates (spheroids) in the pores of polyurethane foam which was used as a cell culture substratum. These spheroids of various cell types express high cell activity for a long period. A practical hybrid artificial live support system composed of a multi-capillary polyurethane foam packed-bed type cell culture module including primary hepatocyte spheroids was developed. The success of the system is indicated by an 80% recovery rate in hepatic failure rats which died in control experiments.

Animals↗

PubMedDate not supplied

Polyurethane elastomer as a possible resilient material for denture protheses: a microbiological evaluation.

A polyurethane elastomer was microbiologically evaluated in vitro for its potential use in resilient denture liners. Specimens were immersed in suspensions of ten selected oral microorganisms; this was followed by viable cell counts at intervals during a 16-week period. Results indicated that the polyurethane neither supported the growth of the organisms nor was it degraded.

Candida↗

PubMed1996

A prospective clinical comparison of two intravenous polyurethane cannulae.

Tissue irritation, as evidenced by phlebitis, associated with Optiva (Johnson & Johnson Medical) and Insyte (Becton Dickinson) polyurethane cannulae was studied. The integrity of the cannulae on removal, the incidence of infection at the cannula site and the factors which influence phlebitis were also examined. One thousand and eight patients had a polyurethane cannula placed for induction of anaesthesia for cardiac surgery. After surgery, the cannula was examined every 24 hours. If evidence of phlebitis occurred, the cannula was removed and sent for culture. All remaining cannulae were removed at 72 hours and the site examined daily for a further three days. There were 503 Optiva and 505 Insyte cannulae studied. The distributions between the two cannulae with respect to patient characteristics, gauge of cannula, number of attempts and difficulty of insertion, cannula site and anaesthetist inserting were similar. The early removal rate for both groups was 47%. Overall phlebitis rate with Optiva was 31% and Insyte 33%. This difference is not statistically significant. The cumulative phlebitis rate increased with time but did not differ between the two types of cannulae. Minor tip distortion or shaft kinking of the cannulae occurred in 16.2% of Optiva and 23.5% of Insyte. This difference is statistically significant and may relate to the slightly more acute taper at the Optiva cannula tip. Both cannulae were similar in clinical performance.

Adolescent↗

PubMed1997

A prospective clinical comparison of two intravenous polyurethane cannulae.

Adolescent↗

PubMed1997

Polyurethane central venous catheters, hydrochloric acid and 70% ethanol: a safety evaluation.

Three groups of polyurethane central venous catheters (CVC) were infused daily for twenty days with 0.1 normal hydrochloric acid, 70% ethanol and normal saline (control) respectively to look for any changes in microscopic structural integrity. A 1 cm segment was cut from the distal end of each CVC daily. All sections were examined in a scanning electron microscope, looking for evidence either of damage to the lumen surface or of wall thinning. No significant damage to the lumen surfaces was observed with either treatment. Sporadic fine surface-pitting appeared late in the study without any clear temporal or treatment-related pattern. The mean CVC wall thickness did not change significantly over the study period (P = 0.15). Qualitative softening of ethanol treated catheters was observed, and this finding limits the recommendations for the use of ethanol. 0.1N HCl does not compromise the structural safety of the catheters, and its use should be considered when polyurethane CVC. become occluded.

Catheterization, Central Venous↗

PubMed2002

Cultivation of porcine hepatocytes in polyurethane nonwovens as part of a biohybrid liver support system.

Many patients suffering from end-stage liver disease cannot be transplanted within reasonable time due to the shortage of donor organs. Bioartificial liver support systems may contribute to the liver regeneration or bridging the time until a liver graft for transplantation becomes available. Nonwovens with integrated oxygenation capacity have been developed and manufactured by melt blow technology using thermoplastic polyurethane. Capillary membranes for oxygenation were integrated into the nonwoven during the processing. The polyurethane nonwoven structures with adapted pore size and high pore volume allow high cell densities in the hepatocyte culture. The three-dimensional cell culture was housed by a flow bioreactor system and was integrated in a closed loop circulation with monitoring possibilities for pressure, pH, temperature, ammonia, and oxygen. Hepatocytes were isolated from rats or pigs by collagenase perfusion and infused into the medium-perfused circulation. Cells showed high viability and hepatocyte specific cytochrome P450-dependent metabolic function in culture (MEGX test).

Albumins↗

PubMed1988

Polyether polyurethanes: biostable or not?

Certain polyether polyurethanes have been shown to be biostable in long-term implant studies. Others retain good bulk properties, but have been shown to develop cracks on their tissue contacting surfaces. Two cracking mechanisms have been identified, in vivo stress cracking and metal ion oxidation. Stress cracking is the result of an interaction between the in vivo mammalian environment and residual stress (strain) in the implanted polymer. Mild autooxidation can be initiated by stress cracking. More extensive autooxidation can be initiated and propagated by corrosion of metallic device components, especially the corrosion products of cobalt. Both mechanisms are controllable, thus, do not necessarily preclude the use of polyether polyurethanes in implantable devices.

Biocompatible Materials↗

PubMed1989

Towards an ideal polyurethane graft for hemodialysis.

Numerous studies have been reported in the field of vascular graft in recent years. The main interest in these studies has focused on producing either a small diameter arterial graft or prosthesis for veins. Polyurethane polymers are emerging because of their superior mechanical, chemically stable and biocompatible nature. Above all, the prominent blood compatibility and elasticity has attracted many investigators to investigate the material for vascular grafts with small diameter. Although several difficulties still remain to be solved, important factors such as anti-thrombogenicity of materials, compliance in long term, porosity, surface microstructure, and permeability are discussed on the basis of many experimental results. In addition, our basic as well as clinical examination of polyurethane graft as a blood access for hemodialysis are presented along with future prospects and difficulties to overcome.

Arteries↗

PubMed1991

An assessment of 2,4 TDA formation from Surgitek polyurethane foam under simulated physiological conditions.

Samples of polyurethane foam used in the manufacture of mammary prostheses were enzymatically treated for a total of thirty days. Papain (a plant thiol endopeptidase which has similar activity to the human lysosomal enzyme cathepsin B) was our enzyme of choice since it has both amidase as well as esterase activity. The experiment was conducted under physiological conditions closely simulating the microenvironment likely to be found around an implanted mammary prosthesis. In our tests, 2,4 TDA was formed during enzymatic attack of this TDI-based polyurethane foam for the first four (4) days, reaching a maximum of 8.3 parts per million. After the initial burst, no further TDA was observed within the limits of detection of the experiment (10 parts per billion). Based on standard risk assessment, this amount of TDA translates into a risk of developing cancer of one in four hundred million.

Animals↗

PubMed1992

Biostability of a non-ether polyurethane.

A new type of medical grade polyurethane elastomer, based upon an ether-free macroglycol, has been developed by VASCOR, Inc. Prior research conducted by others has indicated that an ether-free urethane should be inherently immune to biodegradation and environmental stress cracking. Specimens of the experimental polyurethane, along with positive and negative control materials, were formed into tubing, mounted on mandrels, and implanted in rabbits. After being exposed to the in vivo environment for six months, the specimens were explanted and examined with scanning electron microscopy. No indication of degradation was observed in the experimental polymer or negative control specimens, whereas severe microcracking was seen in most of the positive control specimens.

Animals↗

PubMed1996

Development of silastic polyurethane (Angioflex) materials with antibacterial agent.

Bioimplants incorporated with antimicrobial agents are needed to control Foreign Body Associated Infection (FBAI) in clinical settings. Attempts are made here to develop five different types of polyurethane (Angioflex), viz., (1) bare polymer, (2) bare polymer glow discharged, (3) bare polymer coated with chlorhexidine, (4) chlorhexidine coated polymer glow discharged, and (5) material (4) recoated with another layer of chlorhexidine digluconate. These materials are tested for their in vitro antibacterial effects using disc diffusion technique against five different standard clinical staphylococcus strains, viz., Wood 46 (Staph. aureus), A 182 (Staph. epidermidis), A 313 (Staph. epidermidis), A 61 (Staph. epidermidis), and A 72 (Staph. epidermidis). Maximum antibacterial effects (zone of inhibition) are observed with polyurethanes incorporated with chlorhexidine digluconate (3) and chlorhexidine incorporated and glow discharged (4). Findings of this study indicate that glow discharge does not seem to produce either additive 8r synergistic antibacterial effects with chlorhexidine digluconate coated Angioflex material.

Anti-Bacterial Agents↗

PubMed1995

In vitro determination of the curvatures and bending strains acting on the leaflets of polyurethane trileaflet heart valves during leaflet motion.

Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high levels of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 +/- 0.125 mm (mean +/- standard deviation) were present during leaflet opening, 0.76 +/- 0.24 mm during leaflet closure and 1.01 +/- 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.

Heart Valve Prosthesis↗

PubMed1996

Determination of lubricating film thickness for permeable hydrogel and non-permeable polyurethane layers bonded to a rigid substrate with particular reference to cushion form hip joint replacements.

The lubricating film thickness in a model of compliant layered bearings, using both permeable hydrogels and non-permeable polyurethane elastomers for total hip joint replacements, has been measured using optical interferometry, under both entraining and squeeze-film motion. The film thickness in the lubricated contact was measured for both water and a 40 per cent glycerol solution in water as a function of entraining velocity and squeeze-film time. The measured lubricating film thickness for the permeable hydrogel was compared to that of the non-permeable polyurethane elastomer and little difference was found when the lubricating film thickness was sufficiently large (greater than 150 nm). Comparison of the experimental results and the theoretical predictions based upon elastohydrodynamic lubrication analysis showed good agreement in the entraining experiments where the film thickness was greater than 150 nm. In the squeeze-film experiments the experimental measurements were greater than the theoretical predictions for all squeeze times due to the formation of a central pocket of fluid which was not predicted by the simple theory used. This also occurred for the hydrogels for films greater than 150 nm. For longer squeeze times the film thickness for the hydrogel fell below the theoretical prediction. This was considered to be due to the permeability of the hydrogel reducing the film thickness when the film thickness was less than 150 nm. The permeability of the hydrogel was not modelled in the theoretical lubrication analysis used in this study.

Biomechanical Phenomena↗