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The article begins by reviewing the origin of the use of polyurethane for immobilizing casts, including the incorporation of a zipper, which allows temporary removal of the cast. The formation of the specific polyurethane mixture discussed, Neofrakt, is outlined, as well as its application and specific properties. Finally, Neofrakt's advantages for postoperative care are discussed.
The major aim of this experimental study was the improvement of hemo- and biocompatibility of microvascular allografts. Comparison of polyurethane and ePTFE (expanded polytetrafluoroethene) micrografts did not show a significant advantage of the new material polyurethane. When the endothelial cell seeding method was applied, endothelial cell harvesting from rat fat proved to be very difficult. Therefore, further research on microvessel endothelial cell seeding is planned.
The survival of Staphylococcus epidermidis strain KH 11 in the presence of synthetic high molecular polyurethanes was prolonged in comparison to control experiments performed in the absence of any nutrients. Investigations of the bacteria after contact with the polymers revealed changes in their surface properties and metabolism, in particular a marked induction of urease activity. ESCA (Electron Spectroscopy for Chemical Analysis) measurements detected a decrease in elementary nitrogen in the polyurethane surfaces after incubation with the bacteria. The alterations observed indicate an urease-induced degradation of synthetic polymers by Staphylococcus epidermidis KH 11.
A simple method of enzyme immobilization was investigated which is useful for fabrication of enzyme sensors based on polymeric ion-selective membranes. The enzyme membrane was built by coating a thin hydrophilic polyurethane (HPU) film directly mixed with an enzyme over an underlying polyurethane (PU)-based ion-selective membrane. This highly simple method of enzyme immobilization was applied to the fabrication of a potentiometric butyrylcholinesterase-based biosensor for the determination of organophosphorus pesticides. The enzyme was well entrapped within the HPU film and the intrinsic potentiometric response of the underlying ion-selective PU membrane was not influenced significantly by the outer HPU/enzyme membrane. The enzyme electrode was optimized by changing systematically the composition of the enzyme membrane to evaluate the effect of the changes on sensor response. The sensor was successfully applied to the analysis of paraoxon, an organophosphorus pesticide.
PURPOSE: To assess technical problems related to implantation of a polyurethane stent to treat obstructive epiphora, and to assess the long-term patency of the nasolacrimal system. MATERIALS AND METHODS: Fluoroscopically guided placement of a polyurethane nasolacrimal stent was performed in 70 obstructed lacrimal systems of 62 patients with grade 3-4 obstructive epiphora. Follow-up was conducted for 1-20 months (average, 11.3 months). The obstruction was at the lacrimal sac in six systems, at the junction between the lacrimal sac and the nasolacrimal duct in 60 systems, and at the nasolacrimal duct in four systems. The cause of the obstruction was idiopathic in all cases but was probably residual to dacryocystitis. RESULTS: Of these 70 procedures, stent placement was technically successful in 61 systems (87%). On long-term follow-up, 41 (67.2%) stents remained in place, with resolution or clinical improvement, and 18 (29.5%) stents were removed (because of occlusion in 17 systems), with stent malpositioning in the duct in six cases. There were seven cases of malpositioning in all. Statistical analysis was performed to evaluate patency, compare patency in properly positioned stents and malpositioned stents, and establish the relationship between malpositioning and the need for irrigation to maintain stent patency. Of the total 70 stents originally placed, 41 (58.6%) were still in place and functional at long-term follow-up. At 1 year, 73% of properly positioned stents remained patent versus 0% of improperly positioned stents. Median stent patency in the former group was 20 months and was 1 month in the latter group (P = .00002). Eleven percent of properly positioned stents required irrigation versus 57% of incorrectly positioned stents (P = .01). CONCLUSION: After follow-up for 1 year, recurrence of epiphora brought on by stent obstruction was 28%. Early stent blockage and the need for periodic irrigation may be indicative of malpositioning of the stent.
PURPOSE: To evaluate the effectiveness of a polyurethane-covered Gianturco stent in the palliative treatment of malignant esophageal stricture and fistula. PATIENTS AND METHODS: Twenty-seven patients with recurrent stricture (n = 24), fistula formation (n = 8), or both (n = 5) underwent palliative treatment for aphagia (n = 15) or dysphagia (n = 12). Eight patients had fistulas to the respiratory tract or mediastinum. A 15-F delivery sheath system was passed through the stricture; the inner dilator was removed, and the stent was compressed into the sheath and advanced with a pusher catheter. Follow-up included chest radiography for 3 days and monthly esophagography or endoscopy. RESULTS: Covered stents occluded fistulas and opened strictures in 100% of patients. Food intake was upgraded to liquids in 7% of patients, to soft foods in 37% and to regular foods in 56%. New stricture or fistula occurred in 4% and 7% of patients, respectively. Stent migration occurred in 15% of patients. Twenty-one patients died after stent placement, and average life expectancy was 11 weeks. CONCLUSION: A polyurethane-covered Gianturco stent is effective in the palliation of advanced malignant esophageal strictures and fistulas.
The thermoinactivation of native diisopropylfluorophosphatase (DFPase, EC 3.8.2.1) is highly calcium dependent, first-order kinetic. Deactivation is coupled with a simultaneous reduction in beta-sheet content. We report herein our attempts to enhance the thermostability of DFPase by irreversibly incorporating the enzyme into polyurethane polymers. Immobilized DFPase has biphasic deactivation kinetics. Our data demonstrate that the initial rapid deactivationof immobilized DFPase leads to the formation of a hyperstable and still active form of enzyme. Like native DFPase, DFPase-containing polyurethanes exhibit a calcium-dependent thermostability. Since bioplastics cannot be analyzed by spectroscopy, the structural mechanisms involved in thermoinactivation of immobilized DFPase were determined using PEG-modified DFPase. The thermoinactivation profile of highly modified DFPase mirrors the stepwise deactivation pattern of bioplastics. Spectroscopic studies enable a structural analysis of the hyperstable intermediate.
Hydrosilylation of methyl 10-undecenoate (UDM) with phenyl tris(dimethylsiloxy)silane (PTDS) followed by a reduction of carboxylate groups was used to obtain a silicon-containing polyol with terminal primary hydroxyl groups (PSi194). Biobased silicon-containing polyurethanes, with a silicon content between 1.7% and 9.0%, were prepared from epoxidized methyl oleate-based polyether polyol (P184), PSi194, and 4,4'-methylenebis(phenyl isocyanate) (MDI). The thermal, mechanical, and flame-retardant properties of these materials were examined. The most notable change resulting from the incorporation of PSi194 is the appearance of melting endotherms of variable enthalpy and position and a downward shift in the T(g). The incorporation of silicon does not change the thermal stability but enhances the stability of the char under air atmosphere. Polyurethanes with higher silicon content no longer burn in ambient air without complementary oxygen, which suggests that these biobased materials are very interesting for applications that require fire resistance.
The synthesis of polyurethane microsphere-gold nanoparticle "core-shell" structures and their use in the immobilization of the enzyme endoglucanase are described. Assembly of gold nanoparticles on the surface of polymer microspheres occurs through interaction of the nitrogens in the polymer with the nanoparticles, thereby precluding the need for modifying the polymer microspheres to enable such nanoparticle binding. Endoglucanse could thereafter be bound to the gold nanoparticles decorating the polyurethane microspheres, leading to a highly stable biocatalyst with excellent reuse characteristics. The immobilized enzyme retains its biocatalytic activity and exhibits improved thermal stability relative to free enzyme in solution. The high surface area of the host gold nanoparticles renders the immobilized enzyme "quasi free", while at the same time retaining advantages of immobilization such as ease of reuse, enhanced temporal and thermal stability, etc.
In a previous study, we reported on the synthesis of heparin-immobilized polyetherurethanes containing ester groups in the side chain. In this study, the blood compatibility of heparin-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 polyethylene oxide (PEO) grafting and further prolonged by heparin immobilization. The APTT was prolonged on the PU-C-H and PU-P-H, suggesting the binding of immobilized heparin to the antithrombin III. The percentage of platelet adhesion on the PU was almost the same as that on carboxylic acid-introduced PU (PU-C), but was slightly decreased by PEO grafting and further decreased by heparin immobilization. The release of serotonin from the adhering platelets was slightly suppressed on the PEO-grafted PU yet significantly suppressed on the heparin-immobilized PUs. In the PBMC experiments, the adhesion and activation of the cells were significantly suppressed on the heparin-immobilized PUs, and the amount of interleukin-6 (IL-6) released from the PBMCs stimulated with the surface-modified PUs decreased with a decrease in the PBMC adhesion.
In this study the effects of prestressing, environmental acidity, oxygen content, and temperature on mechanical properties were measured for three polyurethane-based orthodontic elastomeric chains. Specimens of each chain were treated for 10 and 100 days, and their mechanical properties were compared with those of the untreated specimens via stress-relaxation tests. Conditioning treatments were determined to affect the magnitude of residual load after relaxation, with the largest effect due to prestressing. Among the other variables studied, an increase in temperature of the environment appeared to significantly influence the degradation mechanism responsible for the deterioration of the mechanical properties of polyurethane elastomers (p < 0.001); acidity and oxygen content had no significant effects. Force decay profiles from the specimens were derived using a Maxwell-Weichert model consisting of springs and dashpots. This model allows the orthodontist to predict load magnitude supplied by the chain at activation and at any time during treatment.
AIMS: The aim was to investigate the biosorption of chromium, nickel and iron from metallurgical effluents, produced by a steel foundry, using a strain of Aspergillus terreus immobilized in polyurethane foam. METHODS AND RESULTS: A. terreus UFMG-F01 was immobilized in polyurethane foam and subjected to biosorption tests with metallurgical effluents. Maximal metal uptake values of 164.5 mg g(-1) iron, 96.5 mg g(-1) chromium and 19.6 mg g(-1) nickel were attained in a culture medium containing 100% of effluent stream supplemented with 1% of glucose, after 6 d of incubation. CONCLUSIONS: Microbial populations in metal-polluted environments include fungi that have adapted to otherwise toxic concentrations of heavy metals and have become metal resistant. In this work, a strain of A. terreus was successfully used as a metal biosorbent for the treatment of metallurgical effluents. SIGNIFICANCE AND IMPACT OF THE STUDY: A. terreus UFMG-F01 was shown to have good biosorption properties with respect to heavy metals. The low cost and simplicity of this technique make its use ideal for the treatment of effluents from steel foundries.
Thirty ng/mm2 lumbrokinase, a potent fibrinolytic enzyme, was immobilized in a Korean type total artificial heart (KORTAH) valve by photoreaction; polyallylamine was used as a photoreactive linker. Lumbrokinase-immobilized polyurethane valves were then fitted to the total artificial hearts of 3 healthy 50 kg lambs. In the control lamb, the valves were untreated; in one other, only valves on the right were treated; and in the remaining animal, only those on the left. Implants were in place for up to 3 days, and cardiac output was 5 L/min. To facilitate thrombus formation, low doses of heparin were administered. In the control lamb, thrombi was observed only in the inlet parts of the valves. In the other 2 experiments, thrombi formed in untreated control valves but not in lumbrokinase treated valves. The grade of thrombus formation in untreated valves was 1.06+/-1.37 versus 0+/-0 in the treated part by one-sided Student's t-test (p < 0.1). After implantation, fibrinolytic activity was only observed in treated valves by fibrin plate methods. The proteolytic activity of the treated valves was 3 times higher than that of untreated valves using the azocasein method. These data show that lumbrokinase treated polyurethane valves lead to decreased thrombus formation in vivo and that their biocompatibility is therefore greater than that of untreated valves.
BACKGROUND AND STUDY AIMS: Hydrophilic polymer-coated polyurethane (HPCP) stents have a low friction coefficient and a hydrophilic layer, which may reduce biofilm formation and increase the period of stent patency. We compared the patency rates with this new stent with the standard Amsterdam-type polyethylene (PE) stent in a prospective randomized trial. PATIENTS AND METHODS: One hundred patients with an unresectable distal malignant bile duct stricture without a previous drainage procedure were randomly assigned to receive either a HPCP stent or a PE stent. The diameter (10 Fr), length (9 cm) and stent design (Amsterdam type) were similar in both stents. Nine patients were excluded. Forty-four patients received an HPCP stent and 47 patients a PE stent. The diagnoses included carcinoma of the pancreas (n = 78), papilla (n = 1), bile duct (n = 10), and metastases (n = 2). RESULTS: Stent insertion was successful in all patients. Stent dysfunction occurred in 27 of the HPCP stents and 20 of the PE stents, with median stent patency periods of 77 days (95 % CI, 53-101 days) for HPCP stents and 105 days (95 % CI, 42-168 days) for PE stents. The patency period was significantly longer for the PE stent (P = 0.04). Early complications occurred in four patients (4%), one in the HPCP group and three in the PE group. CONCLUSION: Hydrophilic polymer-coated polyurethane stents do not prolong the patency period of biliary stents. In fact, the current standard treatment using polyethylene stents in patients with distal malignant biliary obstruction showed a significantly longer patency period.
Microvascular fibrous polyurethane prostheses (inner diameter 1.5 mm, length 10 cm) were implanted in the abdominal aorta of rats. The prostheses were fixed in a loop. All rats (n = 37) were reoperated 6 weeks after implantation to verify the patency of the prostheses. Eight prostheses were obliterated from various causes. The remaining 29 prostheses were found to be patent 3 months after implantation, which gives a patency rate of 79%. Six weeks and 3 months after implantation 7 and 4 rats, respectively, with patent prostheses were sacrificed. The remaining 18 rats of this study are still alive, more than 4 months after implantation, and will be included in long-term observation studies. The prostheses were examined using both light and scanning electron microscopy. The patent prostheses exhibited macroscopically a clear and transparent inner surface. No obliterative processes could be found either macroscopically or microscopically. Neo-intima ingrowth had advanced +/- 10 mm into the prostheses over the anastomotic line from both ends 3 months after implantation, and was continued by a single endothelium layer for several centimeters. An acellular, stable fibrin film was found inbetween the cellular lining. The neo-intima was anchored at the prosthesis by cellular protrusions extending between the polyurethane fibers. Though 10 cm long prostheses were implanted under unfavorable hemodynamic conditions, a patency rate of 79% was achieved, both 6 weeks and 3 months after implantation. This patency rate could have been higher if evident technical failures had been avoided.(ABSTRACT TRUNCATED AT 250 WORDS)
Soft polyurethane foam was sutured to the sclerae of 28 rabbit eyes in a manner similar to scleral buckling in retinal detachment surgery. During the follow-up period no tissue incompatibility was observed and wound healing appeared to be without complications. Microscopic examination revealed fibrocytes growing through the sponge and after 24 weeks the polyurethane meshwork was completely filled with granulation tissue.
A procedure is described for the fabrication of an extraoral prosthesis with an acrylic resin substructure that retains a magnet sealed from the environment by a polyurethane liner. Velcro is used to enhance the bond of the acrylic substructure to the silicone prosthesis. This procedure results in improved retention of the acrylic resin substructure and protection of the magnet with an encapsulating polyurethane liner.
The results of paraffin gauze dressing and lyophilised polyurethane membrane dressing were studied in a patient with surgically-separated pseudosyndactyly of dystrophic epidermolysis bullosa. Polyurethane membrane dressing decreased the time to epithelialisation and the need for anaesthesia.