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At least 91 records · Page 5Linked to original sources

PubMed1996

Hybrid biomaterials based on the interaction of polyurethane oligomers with porcine pericardium.

Hybrid biomaterials have been produced by the interaction of polyurethane oligomers with both fresh and glutaraldehyde-fixed porcine pericardium. The hybrid biomaterials so formed were translucent with occasional white streaks and/or spots, had increased stiffness (to touch) but remained pliable. No shrinkage temperature was detected for fresh porcine pericardium hybrid up to 100 degrees C compared to porcine pericardium (approximately 67 degrees C) and glutaraldehyde-fixed porcine pericardium (approximately 87 degrees C). Amino acid analysis of the fresh porcine pericardium hybrid showed a reduction in lysine content after active isocyanate-terminated polyurethane oligomers exposure, indicating cross-linking between the polymer and tissue. Histological examination of the hybrid material shows a thin grey coating on both surfaces of the tissue, implying at least surface cross-linking of the tissue with polyurethane. The results suggest that fresh porcine pericardium can be reacted with active isocyanate-terminated polyurethane oligomers to produce hybrid biomaterials with covalent bonding.

Animals↗

PubMed1996

Physical and biological effects of a surface coating procedure on polyurethane catheters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphylococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

Adsorption↗

PubMed1991

Polyurethane film (Opsite) vs. impregnated gauze (Jelonet) in the treatment of outpatient burns: a prospective, randomized study.

As it has been shown that re-epithelialization of partial skin thickness wounds can be accelerated if the wound is kept moist, a prospective, randomized clinical study compared the water vapour-semipermeable polyurethane film, Opsite, with the conventional impregnated gauze dressing, Jelonet, in the treatment of outpatient partial skin thickness burns. Fifty-five patients were included: 30 were treated with the polyurethane film and 25 with the conventional dressing. The patients were followed at regular intervals until healing had occurred and were seen 3 months later for evaluation of residual scars and pigmentation. The burns treated with polyurethane films healed with a median of 10 days, while the conventionally treated burns healed with a median of 7 days (P greater than 0.05). Residual scars were noted in 21 per cent of the patients treated with polyurethane films and in 8 per cent treated conventionally (P greater than 0.05). Prophylactic methods should be publicly stressed since one-quarter of the patients were children of 3 years or less who were scalded by split hot liquids. Furthermore the patients' wounds were only briefly cooled before attending medical care. With small burns we advise that cooling should be prolonged until the pain fades then professional assistance should be sought.

Adolescent↗

PubMed1995

Comparison of transverse strength and dimensional variations between die stone, die epoxy resin, and die polyurethane resin.

This study compared transverse strength and dimensional variations of die stone, epoxy resin, and polyurethane resin. The polyurethane resin was tested unfilled, then filled with 20%, 40%, and 60% silica, by weight. Transverse strength was evaluated for five test strips for each material, and an original calibration plate technique closely simulating intraoral conditions was introduced to evaluate dimensional accuracy. Two series of five measurements for dimensional variations were recorded on each test strip. The first series was 15 minutes after removal from mold and the second series of 5 minutes a week later. The results were computed with a parametric ANOVA and Scheffe's test at 95% confidence level (p < or = 0.05). These results confirmed that die stone recorded the least dimensional change but was rigid and brittle, whereas epoxy resin and polyurethane resin had suitable mechanical properties including greater dimensional variations. Incorporating silica filler in polyurethane resins also reduced their transverse strength and sponsored minimal dimensional variations.

Analysis of Variance↗

PubMedDate not supplied

Preparation of porous polyurethane particles and their use in enzyme immobilization.

Porous polyurethane particles were prepared as follows: (1) Two low molecular weight polymers, namely, poly[methylene(polyphenyl isocyanate)] and poly(propylene glycol) were mixed with stirring at room temperature and allowed to react. (2) The reacted mixture was dispersed with stirring in mineral oil containing small amounts of water, the catalyst dibutyltin dilaurate, and CaCO3 powder. In the presence of the catalyst, the reaction between the two polymers proceeded to completion. Small particles of polyurethane are thus formed which contain mineral oil and CaCO3 as porogens. The particles obtained, separated by filtration, were treated with a solution of HCl in order to generate additional pores, extracted with benzene to eliminate the mineral oil present in the pores, and finally subjected to drying and sieving. The particles were investigated by scanning electron microscopy (SEM), infrared (IR) spectroscopy, and specific surface area measurements. Lipase from Candida rugosa was immobilized by adsorption on the porous polyurethane particles and cross-linked with glutaraldehyde to enhance the stability of the immobilization. The biocatalytic particles were used for the hydrolysis of triacylglycerides. The high activity of the immobilized enzyme, which per enzyme molecule can be higher than that of the free enzyme, reveals that the porous polyurethane particles constitute excellent supports for lipase.

Emulsions↗

PubMed1994

Epicardial administration of ibutilide from polyurethane matrices: effects on defibrillation threshold and electrophysiologic parameters.

Polymer-drug composites known as controlled-release systems have been used effectively to prevent and treat ventricular arrhythmias in experimental studies. We wished to determine if such systems could be useful in reducing ventricular defibrillation energy requirements in an acute canine model without producing undesirable electrophysiologic effects. Ibutilide-polyurethane monolithic controlled-release matrices were formulated with ibutilide fumarate and a polyether polyurethane. In vitro drug-release characteristics of the drug matrices were determined. Two formulations were investigated: (a) 20% ibutilide by weight in polyether polyurethane, and (b) 4% ibutilide/16% dimethyl tartrate in polyurethane. Based on in vitro release studies, 20% ibutilide matrices (25 mg) would provide a 25-kg dog with a dose of 25 micrograms/kg ibutilide in a 2-h acute experimental period, and 4% ibutilide matrices were estimated to provide 3.5 micrograms/kg. We used each of these types of matrices in acute open-chest dog studies to assess electrophysiologic effects and the influence of epicardial controlled-release ibutilide, as compared with intravenous (i.v.) administration, on defibrillation energy thresholds (DFTs), using epicardial defibrillation electrodes. In monophasic defibrillation waveform studies, 20% matrices significantly decreased DFT as compared with a predrug control period [2.54 +/- 0.59 (mean +/- SEM) vs. 7.23 +/- 1.73 J, respectively, p = 0.038]. Administration of the same dose i.v. did not cause significant reduction in energy requirement. With a biphasic defibrillation waveform, 4% ibutilide matrices significantly decreased DFT as compared with control (2.53 +/- 0.34 vs. 3.42 +/- 0.46 J, respectively, p = 0.003). Administration of an equivalent i.v. dose did not cause a significant reduction in biphasic energy requirement. Both types of controlled-release systems significantly prolonged refractoriness and conduction times of ventricular extrastimuli as compared with vehicle. No proarrhythmia events were observed. Epicardial polymeric controlled-release ibutilide significantly prolonged ventricular refractoriness and conduction and thus may enhance antiarrhythmia activity. In addition, controlled-release ibutilide formulations significantly decreased DFT requirements. Thus, ibutilide-polymeric controlled-release matrix systems may be useful in conjunction with implantable defibrillators in preventing ventricular arrhythmias and reducing defibrillation energy requirements.

Animals↗

PubMed1990

Natural-Y Même polyurethane versus smooth silicone: analysis of the soft-tissue interaction from 3 days to 1 year in the rat animal model.

The polyurethane foam-covered breast prosthesis is experiencing increased clinical use. The polyurethane is felt to be responsible for altering capsule formation and reducing the contracture rate. This study characterizes the soft-tissue response to the Natural-Y Même polyurethane foam versus smooth silicone in a rat model. Implants were fashioned from an unbacked polyurethane foam specimen used to cover the Natural-Y prosthesis, a silicone shell covered with the Natural-Y foam, and a smooth silicone control. Materials were placed subcutaneously into the backs of male Lew/SsN rats (n = 81) for 3, 7, 14, and 28 days and 3, 6, and 12 months. Implants were then harvested with their soft-tissue response and evaluated histologically. Analysis demonstrates that microstructuring of a surface, as opposed to a smooth material, will dramatically alter the early, intermediate, and late wound-healing events. The soft-tissue response was observed to be dependent on implant site, material chemistry, and morphology as characterized by exudate formation, macrophage invasion, multinucleated giant cell formation, collagen deposition, foam degradation, and angiogenesis.

Animals↗

PubMed1991

Comparative experience with smooth and polyurethane breast implants using the Kaplan-Meier method of survival analysis.

Smooth-walled silicone implants have been widely used in breast surgery. Capsular contracture, causing undesirable firmness and spherical deformity, has been a common problem. Recent studies suggest that polyurethane-covered breast implants are associated with a lower incidence of capsular contracture. The statistical methodology employed in some of these studies, however, may be subject to criticism. Between July of 1984 and June of 1990 (72 months), 427 polyurethane breast implants were used in 279 patients and 439 smooth prostheses were used in 250 patients for a variety of aesthetic and reconstructive procedures. The occurrence of capsular contracture was carefully monitored and then analyzed using the Kaplan-Meier method of survival analysis. This method is particularly well suited to analysis of these types of clinical data because it allows for the fact that contractures occur at varying intervals after surgery and that follow-up of patients is incomplete. The probability of capsular contracture with smooth-walled prostheses was found to be significantly greater than with polyurethane-covered implants in each group of patients studied (p less than 0.05). Other complications occurred at a similar rate regardless of prosthesis type. This study supports the belief that polyurethane breast implants have a lower contracture rate; furthermore, it introduces the Kaplan-Meier method for analyzing the outcome of alternative plastic surgical therapies.

Breast↗

PubMed1992

The biomechanical and histopathologic effects of surface texturing with silicone and polyurethane in tissue implantation and expansion.

There has been considerable interest in determining the effect of morphologic alterations of prosthetic surfaces on capsule response in breast surgery. The purpose of this study was to provide a precise, three-dimensional evaluation of soft-tissue response to surface modifications in both implantation and expansion. Expandable 100-cc prostheses were designed with one of three surfaces: textured silicone (Biocell), standard smooth silicone, or polyurethane (Natural-Y, Meme). A new submuscular implantation site in the rabbit was developed. Each animal randomly received a smooth-surface device on one side and either a textured silicone or polyurethane device on the other. In one group of animals, the prostheses were expanded monthly. Capsular response was evaluated monthly in vivo using standardized techniques as well as biomechanical methods for up to 6 months in the expander group (n = 7 to 16) and 8 months in the implant group (n = 7 to 15). Analysis of biomechanical and histologic data revealed that prosthetic surface morphology can specifically alter capsular response. Polyurethane was the only effective surface in preventing capsular contracture in implantation. In expansion, both textured silicone and polyurethane surfaces resulted in significantly less capsular contracture and less resistance to expansion than comparable smooth-surfaced controls. Statistical comparisons reveal that the biomechanical methods utilized in this study provide the most precise and objective method of defining overall soft-tissue contracture around implanted biomaterials.

Animals↗

PubMed1996

In vitro function and durability assessment of a novel polyurethane heart valve prosthesis.

While flexible-leaflet, central-flow prosthetic heart valves promise relief from anticoagulation therapy, they continue to be restricted by inadequate durability. In consequence, a novel trileaflet valve, made entirely from polyurethane, has been developed. A batch of 6 consecutively manufactured polyurethane valves was subjected to hydrodynamic function and accelerated fatigue testing. Computerized data acquisition and control systems have been introduced to improve valve testing methodologies. In terms of hydrodynamic function, the polyurethane valve demonstrates transvalvular pressure gradients similar to those for a bioprosthetic valve (Carpentier-Edwards) and levels of retrograde flow significantly less than those for either the bioprosthetic valve or a bileaflet mechanical valve (St Jude Medical). The equivalent of 10 years of cycling without failure has been exceeded by all 6 polyurethane valves in accelerated fatigue tests with 2 valves remaining intact after 674 million cycles (equivalent to approximately 17 years) in continuing tests. Highspeed photography revealed considerable differences in leaflet motion between valves cycled at accelerated and physiological rates.

Biocompatible Materials↗

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↗

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↗

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↗

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↗