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At least 757 records · Page 42Linked to original sources

PubMed2005

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite-polyurethane composite electrode.

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite-polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L(-1); pH 7.4). Analytical curves were constructed under optimized conditions (f=60s(-1), DeltaE(a)=50 mV, DeltaE(I)=2 mV) and detection and quantification limits of 6.4x10(-8) mol L(-1) (12.1 microg L(-1)) and 5.2x10(-6) mol L(-1) (0.9 mg L(-1)), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9x10(-6) mol L(-1) dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.

Dopamine↗

PubMed2005

Examples of the application of optical process and quality sensing (OPQS) to beer brewing and polyurethane foaming processes.

Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near-infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant.

Beer↗

PubMed2000

The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol.

A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam (PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR), packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation rate of phenol (q(s)max) decreased in the order: PBRC (598 mg l(-1) h(-1)) > PBR (PU, 471 mg l(-1)h(-1)) > PBR(SG, 394 mg l(-1) h(-1)) > FBR (PU, 161 mg l(-1) h(-1)) > FBR (SG, 91 mg l(-1) h(-1)). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100-200 microm thick layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized in colloidal SiO2 enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic packing.

Biodegradation, Environmental↗

PubMed2000

Use of microorganism-immobilized polyurethane foams to absorb and degrade oil on water surface.

Highly oil-absorbent polyurethane foam (PUF) materials were obtained by polymerizing polyether polyol mixture and carbodiimide-modified D-methyl diisocyanate in a weight ratio of 10:2. The foam materials were prepared to contain inorganic nutrients (slow-release fertilizer; SRF) and oil-degrading yeast cells, Yarrowia lipolytica 180, to be applied for removal of oil films on surface waters through absorption and biodegradation after oil spills. PUFs absorbed 7-9 times their own weight of Arabian light crude oil and the oil absorbency appeared to improve as the ratio of surface area to foam weight increased. PUFs showed excellent floatability which was maintained for more than 6 months in sea water, and less than 5% of the absorbed oil was released when the foams were left on water for more than 10 days. For immobilization of yeast cells into PUFs, various immobilization techniques were tested to compare their oil degrading ability and the maintenance thereof. All immobilized cells showed oil degrading abilities as good as those of free cells immediately after the preparation of PUFs, however, the activity of chitin-immobilized cells remained at a high level for the longest period of preservation. The high efficiency of oil absorption and oil degradation by PUF-immobilized yeast cells suggested that PUF-immobilized cells have a high potential as a bioremediation technique for the treatment of oil films on surface waters.

Absorption↗

PubMedDate not supplied

An improved method of removing polyurethane foam-covered gel prostheses.

One of the advantages of polyurethane foam-covered prostheses has been that in the first 5 to 10 years after their use, the amount of capsular contraction was found much less than when similar "slick" prostheses were used. Another advance was their fixation to the surrounding tissue thus giving a more natural appearance and movement with the muscles when the arms were moved in any direction. The formation of a thick capsule also acted as a protection against gel granuloma due to rupture of the prosthesis and has been thought to be a factor in the lower capsule contraction rate. The greatest disadvantage has been that its removal was extremely difficult and this has continued up until the technique described in this paper has been introduced.

Breast Implants↗

PubMedDate not supplied

A ten-year experience using polyurethane-covered breast implants.

The purpose of this study is to disclose the low incidence (0.98%) of capsular contracture using polyurethane-covered silicone gel breast implants. Four hundred seven surgical interventions were performed during the 10-year period, 404 for hypomastia and 3 for breast reconstruction.

Breast↗

PubMedDate not supplied

Polyurethane-covered Nitinol Strecker stents as primary palliative treatment of malignant biliary obstruction.

PURPOSE: To evaluate the clinical efficacy of the polyurethane-covered Nitinol Strecker stent in the treatment of patients with malignant biliary obstruction. METHODS: Twenty-three covered stents produced by us were placed in 18 patients with malignant biliary obstruction. Jaundice was caused by cholangiocarcinoma (n = 5), pancreatic cancer (n = 6), gallbladder cancer (n = 4), metastatic lymph nodes (n = 2), and tumor of the papilla (n = 1). RESULTS: The mean patency period of the stents was 37.5 weeks (5-106 weeks). Recurrent obstructive jaundice occurred in two patients (11%). Adequate biliary drainage over 50 weeks or until death was achieved in 17 of 18 patients (94.4%). Late cholangitis was observed in two patients whose stents bridged the ampulla of Vater. Other late severe complications were not encountered. CONCLUSION: Although more study is necessary, our results suggest the clinical efficacy of our covered Nitinol Strecker stent in the management of obstructive jaundice caused by malignant diseases.

Adult↗

PubMed2001

Covered Gianturco stent for tracheal stricture: application of polychlorovinylidene and polyurethane as covering materials.

The aim of this study was to assess the efficacy and safety of thin membranes of polychlorovinylidene (PCV) or polyurethane (PU) as covering materials for Gianturco stents in the treatment of severe tracheal stricture caused by intraluminal tumor. Manufactured Gianturco stents covered with PCV or PU membrane were used to treat six malignant and one benign tracheal stricture. The initial results, complications, clinical follow-up, bronchoscopic findings, and three autopsy microscopic examinations were reviewed. Informed consent was obtained after the nature of the treatment had been fully explained before every procedure. The stents successfully dilated the tracheal strictures, providing immediate relief of respiratory symptoms in all patients with no major complications. During the follow-up period, the covering materials prevented tumor ingrowth until death or intraluminal granuloma formation. Autopsies proved that no histological change occurs in the tracheal mucosa in response to the presence of PCV or PU; however, ulcer formation occurred in one patient and penetration of the stent struts into the tracheal wall in two. Bloody sputum with ulcer formation, minimal granuloma formation at the distal end of the stent, and abnormal bacterial load in the sputum were long-term complications. The Gianturco stent covered with PCV or PU membrane is a useful option as a palliative treatment for malignant and an emergent salvage for benign tracheal stricture, because both materials are thinner and less voluminous than the others. However, the indications for its use are limited to patients with poor prognoses, because hemoptysis, granuloma formation, and bacterial propagation remain problematic.

Aged↗

PubMed1999

[Evaluation of polyurethane stent implantation for the treatment of complete obstruction of the nasolacrimal system: 8-month follow-up and complications].

UNLABELLED: Dacryocystorhinostomy is still the standard procedure complete stenosis of the nasolacrimal duct. New methods try to preserve the natural lacrimal pathway. Song implanted in 1995 a nasolacrimal polyurethane stent through the nasolacrimal duct. The results and complications of this new method are described in this prospective study. METHODS: Thirty consecutive patients with complete obstruction of the nasolacrimal duct or lacrimal sac were included in the study. The stenosis was localized by dacryocystography. The ages ranged from 22 to 87 years (mean, 58.9 +/- 16 years). Dacryocystography was performed immediately, 4 weeks and 8 months after the procedure to verify the position and patency of the stent. RESULTS: Twenty-five short (35 mm) and 5 long (45 mm) stents were implanted. Twenty-four of 30 patients after 4 weeks and 9 of 10 patients after 8 months had reduced or no complaints. In 1 patient the stent was obstructed. Forceful irrigation with saline solution permitted recanalization. In 1 patient the stent had moved into the upper canaliculus. Because of irritation of the canaliculus it had to be pulled out after 2 months. CONCLUSION: The follow-up is still too short to recommend stent implantation as a real alternative to dacryocystorhinostomy. The main advantages are that the procedure is faster, no incision is necessary, and the local anesthesia is easier. The disadvantage is the need for X-ray examination.

Adult↗

PubMed2002

Exposure and nasal inflammation in workers heating polyurethane.

OBJECTIVE: To test the hypothesis that exposure to thermal-degradation products of polyurethane (PUR), particularly isocyanates, induced nasal inflammation. METHODS: Thirty-eight workers -14 with a history of work-related nasal symptoms (WRS/Nose), and 15 referents without such history - exposed to sprayed and heated PUR glue, were studied with regard to biomarkers of isocyanate exposure [4,4'-diphenylmethane diisocyanate (4,4'-methylenediphenyl diisocyanate; MDI) and 2,4- and 2,6-toluene diisocyanate (TDI), determined as 4,4'-diphenylmethane (U-MDX) and 2,4- and 2,6-toluene (U-2,4 and U-2,6-TDX) diamine in hydrolysed urine and nasal lavage fluid (NAL)], inflammation [albumin; eosinophilic cationic protein (ECP); myeloperoxidase (MPO) and cells in NAL], serum IgG specific for MDI (S-IgG-MDI) and TDI (S-IgG-TDI), and nose symptoms. Nine unexposed office workers were also examined. RESULTS: The exposure to sprayed and heated PUR glue, especially when heated by gun, was associated with the presence of biomarkers of isocyanate exposure in urine; after work the levels [median (range)] in all workers were: U-MDX 0.32 (<or=0.1-1.5); U-2,6-TDX 0.33 (<or=0.1-0.71) microg/g creatinine. Also, 5/38 workers had detectable levels in NAL. Furthermore, the biomarkers of inflammation in NAL - albumin ( P<or=0.05; Kendall), MPO ( P=0.01), and neutrophils ( P<or=0.01) - showed similar patterns of relationships with the exposure to glue heated by guns. After work, workers who had complained of WRS/Nose had higher levels of albumin (medians 3.5 vs. 1.9 mg/l; P=0.05, Mann-Whitney U-test) and MPO (14 vs. 11 microg/l; P<or=0.05) in NAL than those who had had no such complaints. U-2,6-TDX, as well as S-IgG-MDI and S-IgG-TDI, were associated with increased levels of the inflammation biomarkers, U-2,6-TDX also with the symptoms. As expected, acute symptoms after exposure were associated with the inflammation biomarkers. CONCLUSIONS: The present data indicate that thermal degradation products of PUR induced a 'chronic' rhinitis. At exposure, there was an accentuation of symptoms; the signs of acute inflammation were less obvious.

Automobiles↗

PubMed2004

Characterization of molecular structures and properties of polyurethanes using molecular dynamics simulations.

Thermotropic polyurethanes with mesogenic groups in side chains were prepared from two diisocyanates and four diols with stoichiometric ratios of reactive isocyanate (NCO) and hydroxy (OH) groups. Their thermal behavior was determined by differential scanning calorimetry. The effect of structure modifications of the diisocyanates and diols, in particular changes in the mesogen, were investigated. Introduction of mesogenic segments into the polymers suppresses the ordering. Stiff end substituents (phenyl and alkoxy groups) of the mesogens stabilize the mesophases to such an extent that the negative influence of long polymer chains is compensated and the liquid-crystalline properties are recovered. All-atom molecular dynamics simulations in the Cerius2 modeling environment were carried out to characterize the structures of the polymers. Analysis of the dynamic trajectories at 20, 100, 120 and 170 degrees C revealed changes in conformation of macromolecules, which correlate with DSC measurements.

Calorimetry↗

PubMed2003

Long-term follow-up of polyurethane vascular grafts for hemoaccess bridge fistulas.

The new polyurethane vascular graft (PVG) has been reported to be better than the expanded polytetrafluoroethylene (PTFE) graft in terms of early access and prompt hemostasis, but long-term patency and safety of PVGs have not been investigated objectively. To evaluate late clinical outcome of the PVG, we compared the complication and patency rates of stretch PTFE grafts with those of PVGs implanted for hemodialysis vascular access. Subjects were 53 patients who received 58 arteriovenous grafts between October 1997 and July 2000. They were divided in a prospective fashion into two groups according to the type of implanted graft: PVG ( n = 30) or PTFE ( n = 28). The study group comprised 27 men and 31 women with a mean age of 61.7 +/- 10.9 years (range: 23-84 years). The average number of previous accesses was 5.1 +/- 3.1 (range: 0-12). There were no differences between the groups in term of age, sex, body surface area, etiology of renal disease, presence of diabetes, previous access procedures, anatomical positions of grafts, or mean follow-up period. Primary patency rates for the PVG and PTFE grafts were equivalent at 1 year (60.7% vs. 56.5%) and at 2 years (54.7% vs. 51.8%). Similarly, secondary patency rates for the two groups did not differ at 1 year (78.7% vs. 79.9%) or at 2 years (78.7% vs. 69.3%). These findings indicate that the PVG is an acceptable alternative to the PTFE graft for blood access.

Adult↗

PubMed2005

Segmented polyurethane modified by photopolymerization and cross-linking with 2-methacryloyloxyethyl phosphorylcholine polymer for blood-contacting surfaces of ventricular assist devices.

To improve the biocompatibility of pulsatile ventricular assist devices (VADs), the blood-contacting surface of the segmented polyurethane (SPU) diaphragm employed in an electromechanical VAD was modified by introducing 2-methacryloyloxyethyl phosphorylcholine (MPC) units into its surface and forming an interpenetrating polymer network (IPN) structure, which contained independently cross-linked MPC polymer and SPU. The SPU diaphragm modified with an IPN structure was then assembled into a target test pump and underwent continuous pump operation at 37 degrees C for 2 weeks in a simulated systemic circulation using a mock circulatory loop. The surface characteristics of the pump diaphragm after 2 weeks of pump operation were then analyzed with an X-ray photoelectron spectroscope (XPS) and gold-colloid-labeled immunoassay. The XPS surface analysis of the IPN-modified SPU indicated the firm anchoring of MPC units even after 2 weeks of pump operation (the phosphor : carbon ratio was reduced by only 0.09%). The IPN-modified diaphragm prevented protein adsorption as well as cell adhesion in comparison to the unmodified SPU surface. This result thus validated that (1) the IPN structure could firmly secure MPC units to the SPU surface even in a high-mechanical-stress and high-shear environment, (2) the antithrombogenic power of MPC units remained unchanged after 2 weeks of continuous exposure to a high-shear environment, and (3) the IPN modified SPU cross-linked with MPC could be a powerful antithrombogenic surface for blood pumps used for chronic circulatory support of cardiac patients.

Biocompatible Materials↗

PubMed2006

Isolation of marine bacteria by in situ culture on media-supplemented polyurethane foam.

Polyurethane foam (PUF) supplemented with various agar media was used in situ to trap marine bacteria and it consequently provided a substrate on which they could be cultivated while exposed to natural seawater in the coral reef area. The bacterial population on the PUF blocks was analyzed by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rDNA fragments. Changing the composition of the cultivation medium in the PUF blocks and selecting different sampling sites resulted in different bacteria being detected on the PUF blocks. For example, iron-utilizing (IU) bacteria, siderophore-producing (SP) bacteria, and petroleum-degrading (PD) bacteria were isolated from PUF blocks and it was discovered that IU and SP contained iron and PD contained hydrocarbon. This method opens up the possibility for isolating novel and useful marine bacteria.

Bacteria↗

PubMed2006

Spatio-temporal distributions of metal ions and Taxol of Taxus cuspidata cells immobilized on polyurethane foam.

Distinct spatio-temporal variations of metal ions and Taxol production were observed for Taxus cuspidata cells immobilized on polyurethane foam. The Taxol content in the inner foam layer reached 215 microg g(-1) at day 30, which was 40-fold higher than that in the outer foam layer, and the Ca2+ and Mg2+ contents were 5.3 and 3.7 times higher, while the K+ content was 5.5 times lower. Thus higher intracellular Ca2+ and Mg2+ contents and lower intracellular K+ content may favor the Taxol biosynthesis in immobilized Taxus cuspidata.

Antineoplastic Agents, Phytogenic↗

PubMed2005

Evaluation of cell culture on the polyurethane-based membrane (Tegaderm): implication for tissue engineering of skin.

BACKGROUND: The use of polymer-based delivery systems, on which cells are cultured and transferred, improves the ease of handling and transfer of the keratinocytes. A transparent polymer also allows observation of cell growth prior to grafting as well as re-epithelialization after grafting to the wound. We have developed techniques for cultured keratinocytes on Tegaderm (3M), an inexpensive and easily available polyurethane-based wound dressing, for treatment of burn and chronic wounds. In this study, we evaluate cell culture characteristics of three different cell types, human epidermal keratinocytes, human dermal fibroblasts and pig bone marrow mesenchymal stem cells on Tegaderm membrane. METHODS: Cells were isolated from human skin or pig bone marrow and cultured on membranes for a period of five days. Cell proliferation was assessed by colorimetric assay (MTT) and scanning electron microscopy. RESULTS AND CONCLUSIONS: This study confirms that Tegaderm membranes support attachment and growths for these cell types, with those growth characteristics are similar, if not as good as that of optimal condition of tissue culture plastics. Data from our study suggest that Tegaderm membranes can be used, modified and developed further as an economical and easily available material for tissue engineered skin.

Animals↗

PubMed2005

Preparation of a reticulated polyurethane foam grafted with poly(acrylic acid) through atmospheric pressure plasma treatment and its lysozyme immobilization.

We successfully introduced peroxide groups onto the surface of PU(Polyurethane) foam(10 PPI) through one atmospheric pressure plasma treatment and sequentially grafted PAAc(poly(acrylic acid)) on the surface of PU through radical copolymerization. The plasma treatment can generate large amount of peroxides on the surface of PU foam and the peroxide groups act as initiators for further grafting of PAAc in the monomer solution. To introduce large amount of peroxides on the surface of PU foam, we studied the effect of plasma rf-power and treatment time on the maximum grafting of PAAc. Through this study, we found that the optimum plasma treatment condition was the rf-power of 100 W and the treatment time of 100 s. On the other hand, we also studied the effect of graft reaction conditions such as temperature, monomer concentration and reaction time on the change of grafting degree (GD). The GD increased with increasing temperature and increased with reaction time before it leveled off at 3 h after reaction started. At low concentration of AAc, the GD was very low but it showed a maximum at the monomer concentration between 60 and 70%. The surface of the modified PU foam was qualitatively and quantitatively analyzed through the use of FT-IR and weight measurement, respectively. We also observed the surface change before and after plasma induced graft co-polymerization through photo and SEM analysis. Finally, we confirmed that the PU foams grafted with PAAc successfully immobilized lysozyme and other proteins from hen egg white.

Acrylic Resins↗

PubMed2005

Inflammatory response to a novel series of siloxane-crosslinked polyurethane elastomers having controlled biodegradation.

A series of polyurethane polymers was synthesized with increasing proportions of silicone in the form of polydimethylsiloxane (PDMS) utilised as a cross-linking agent, based on an aromatic, non-biostable polyetherurethane (PEtU). Eight formulations ranging from 0-50% PDMS were constructed into porous and non-porous films. These were implanted subcutaneously in rats, both unstrained and 100% strained, for 3 and 6 months. Degradation was determined by FTIR-ATR. Porous films were implanted for 6 and 12 months intramuscularly in both rats and rabbits. These were explanted and examined for inflammatory cell markers by immunohistochemistry. Both low and high percentages of siloxane gave rise to increased degradation, with 20-40% PDMS resulting in the least degradation. Infrared spectral changes correlated well with both visual examination and observation by SEM. Changes to the concentration of siloxane gave rise to differences in the thickness of fibroblastic capsule and infiltration of inflammatory cells in both films & scaffolds. Cellular infiltration was greatest in the films with lower siloxane concentrations. Macrophage activation (MHC-I & MHC-II expression) was least in the higher siloxane variants. It is concluded that by varying the siloxane content in the PEtU matrix we can obtain an acceptable inflammatory response with a relatively short degradation time.

Animals↗