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At least 829 records · Page 46Linked to original sources
PubMed2005

On-line preconcentration/determination of lead in Ilex paraguariensis samples (mate tea) using polyurethane foam as filter and USN-ICP-OES.

The present paper proposes an on-line preconcentration procedure for lead determination in Ilex paraguariensis (St. Hilaire) samples by ultrasonic nebulization associated to inductively coupled plasma optical emission spectrometry (USN-ICP-OES). It is based on the precipitation of lead(II) ion on a minicolumn packed with polyurethane foam using 2-(5-bromo-2-pyridilazo)-5-diethylaminophenol (5-Br-PADAP) as precipitating reagent. The collected analyte precipitate was quantitatively eluted from the minicolumn with 20% (v/v) nitric acid. An enhancement factor of 225-fold was obtained (15 for USN and 15 for preconcentration). The detection limit (DL) value for the preconcentration of 10.0 ml of sample was 40.0 ng/l. The relative standard deviation (R.S.D.) was 3.0% for a Pb concentration of 1 microg/l, calculated from the peak heights obtained. The calibration graph using the preconcentration system for lead was linear with a correlation coefficient of 0.9997, at levels near the detection limits up to at least 100 microg/l. The preconcentration procedure was successfully applied to the determination of lead in mate tea samples.

Beverages↗
PubMed2006

Preconcentration system for cadmium and lead determination in environmental samples using polyurethane foam/Me-BTANC.

In this work, polyurethane foam (PUF) loaded with 2-(6'-methyl-2'-benzothiazolylazo)chromotropic acid (Me-BTANC) was packed in a minicolumn and it was used in an on-line preconcentration system for cadmium and lead determination. Optimum hydrodynamic and chemical conditions for metal sorption were investigated. The effects of several foreign substances on the adsorption of cadmium and lead were also reported. The enrichment factor obtained was 37 (Cd and Pb) for 180 s preconcentration time. The proposed procedures allowed the determination of metals with detection limits (3 sigma) of 0.80 and 3.75 microg L(-1) (0.10 and 0.47 microg g(-1) of solid sample) for cadmium and lead, respectively. The precision of the procedures was also calculated: 3.1 (Cd 10 microg L(-1)) and 4.4% (Pb 100 microg L(-1)). The accuracy of the procedure was checked by analysis of the certified reference materials Spinach Leaves and Fish Tissue. Cadmium and lead contents in environmental samples (black tea, spinach leaves, natural and tap water) were determined by applying the proposed procedure.

Animals↗
PubMed2006

Transport behavior of n-alkane penetrants into castor oil based polyurethane-polyester nonwoven fabric composites.

Castor oil based polyurethane (PU)-polyester nonwoven fabric composites were fabricated by impregnating the polyester nonwoven fabric in a composition containing castor oil and diisocyanate. Composites were fabricated with two different isocyanates such as toluene-2,4-diisocyanate (TDI) and hexamethylene diisocyanate (HMDI). Transport behavior of n-alkane penetrants (pentane, hexane and heptane) into both PUs and PU-polyester nonwoven fabric composites were studied. Sorption studies were carried out at different temperatures. From the sorption results, the diffusion (D) and permeation (P) coefficients of penetrants have been calculated. Significant increase in the diffusion and permeation coefficients was observed with increase in the temperature of sorption experiments. Drastical reduction in diffusion and permeation coefficients was noticed in the composites compared to neat PUs. Attempts were made to estimate the empirical parameters like n, which suggests the mode of transport and K is a constant depends on the structural characteristics of the composite in addition to its interaction with penetrants. The temperature dependence of the transport coefficients has been used to estimate the activation energy parameter for diffusion (E(D)) and permeation (E(P)) processes from Arrhenius plots. Furthermore, the sorption results have been interpreted in terms of the thermodynamic parameters such as enthalpy (DeltaH) and entropy (DeltaS).

Adsorption↗
PubMed2006

FTIR spectroscopic characterization of polyurethane-urea model hard segments (PUUMHS) based on three diamine chain extenders.

Six polyurethane-urea model hard segments (PUUMHS) were prepared by a solution method based, respectively, on two isocyanates: 4,4'-methylene-diphenyl-diisocyanate (MDI), 4,4'-methylene-dicyclohexyl diisocyanate (HMDI) and three amine chain extenders: ethylene diamine (EDA), methylene-bis-ortho-chloroaniline (MOCA), 2,4-diamino-3,5-dimethylsuphylchlorobenzene (DDSCB). FTIR was used to study their spectroscopic characterization. The main FTIR bands of the six samples were assigned and compared. It was found that most of N-H and C=O are H-bonded in these PUUMHS. However, the N-H in three MDI based PUUMHS is all in the stronger H-bond state than that in their corresponding HMDI based while the C=O in three HMDI based PUUMHS is all in the stronger H-bond state than that in their corresponding MDI based, respectively. In addition, the order of the H-bond strength in HMDI based PUUMHS is MOCA, DDSCB and EDA whether according to nuN-H or nuC=O band wavenumbers, which is, however, different from that in MDI based PUUMHS. Moreover, the HMDI based PUUMHS shows obvious double amide III bands while the MDI based has only prominent one. The results are discussed according mainly to the different characteristics of the three chain extenders as well as the structure difference between MDI and HMDI.

Diamines↗
PubMed2001

[Composite, non-resorbable parietal prosthesis with polyethylene terephtalate-polyurethane (HI-TEX PARP NT): prevention of intraperitoneal adhesions. Experimental study in rabbits].

The authors report an experimental study in the rabbit with a new composite non absorbable mesh in Polyethylene Terephtalate-Polyurethane used for incisional hernia repair in intraperitoneal positioning. This new mesh has one permeable side in polyethylene terephtalate for rapid tissue fixation and another side in polyruethane, hydrophob in order to avoid cell penetration. Eighteen rabbits were operated. A wound was created in aponeurose, muscle and peritoneal abdominal wall. The mesh was placed in intraperitoneal positioning and was taken off at 4, 9 and 13 months for histologic examination and electronic microscopical examination. Tolerance, adhesion, tissular reaction and neoperitoneum formation have been studied. All the meshes were well integrated and without sepsis. In 18% of cases small and monocclusive intraperitoneal adhesions were found. This new composite mesh in intraperitoneal positioning gave good results at medium-term in the rabbit. It's an attractive alternative for incision hernias repair with intraperitoneal mesh.

Abdominal Muscles↗
PubMed1985

Percutaneous transhepatic internal drainage using polyurethane double-pigtail endoprostheses.

Relief of obstructive jaundice by the percutaneous transhepatic insertion of an endoprosthesis is now a well recognised and common radiological procedure. We report the successful insertion of polyurethane double-pigtail stents (made for transpapillary endoscopic insertion) by the percutaneous transhepatic route in five patients. Our experience indicates that these stents are as effective in relieving jaundice as, and less traumatic and easier to insert than, the larger varieties in common use.

Cholestasis↗
PubMed2000

Hydrophilic hydromer-coated polyurethane stents versus uncoated stents in malignant biliary obstruction: a randomized trial.

BACKGROUND: Hydromer-coated polyurethane stents (HCPS) have a low coefficient of friction that may reduce sludge formation and potentially increase stent longevity. METHODS: Eighty-three patients (39 men, mean age 69.3 years) with malignant mid or distal bile duct strictures were prospectively randomized to receive either 10F HCPS (n = 40) or standard polyethylene stents (n = 43). RESULTS: Fifteen patients (18.1%) underwent surgery after stent insertion. Six patients were lost to follow-up (7.2%), whereas 34 died of the underlying disease without evidence of stent occlusion (15 HCPS group and 19 polyethylene group). Median survival was 75 days (range 15 to 372 days) and 108 days (range 25 to 325 days) in the HCPS and polyethylene stent groups, respectively (p = not significant). Stent occlusion was observed in 25 patients (42%), 16 with HCPS stents and 9 with polyethylene stents, with a median patency of 103 days (range 40 to 280 days) and 68 days (range 32 to 175 days), respectively (p = not significant). CONCLUSIONS: HCPS do not appear to provide significant clinical advantages in terms of stent longevity over standard plastic prostheses.

Aged↗
PubMed1998

Determination of airborne, volatile amines from polyurethane foams by sorption onto a high-capacity cation-exchange resin based on poly(succinic acid).

A high-capacity carboxylic acid-functionalized resin prepared by ring-opening metathesis polymerization based on cross-linked endo,endo-poly(norborn-2-ene-5,6-dicarboxylic acid) was used for the sampling of volatile, airborne amines from polyurethane (PU) foams. Six tertiary amines which represent commonly used promotors for the formation of PUs from diisocyanates and polyols, namely pentamethyldiethylenetriamine, diazabicyclooctane, N-methylmorpholine, N-ethylmorphine, 1,4-dimethylpiperazine and N,N-dimethylethanolamine, were sorbed onto the new resin. The sorption behavior of the new material was investigated in terms of loading capacities, the influence of concentration, flow-rate as well as of the amount of resin. Breakthrough curves were recorded from each single component as well as of mixtures thereof. Finally, the resin was used for the sampling of amines evaporating from PU foams applied in buildings. Further information about time dependent concentration profiles were obtained using a combination of GC-MS and Fourier transform IR spectroscopy.

Adsorption↗
PubMed1978

Polyurethane elastomers for facial prostheses.

A review of the polyurethane elastomers used for facial prostheses has been presented. A description of the casting technique was given. The materials require accuracy and care in handling to insure the successful casting of a prosthesis. They seem to simulate the characteristics of the facial tissues and are more durable and comfortable than previously used materials. Over 300 patients have been exposed to or treated with these materials without evidencing significant adverse tissue reaction. In spite of the improvements that these materials present over previous ones (PVC and silicones), much work is still required to understand their behavior and their physical and mechanical characteristics and to compensate for the metameric phenomenon.

Biocompatible Materials↗
PubMed1991

Polyurethane internal ureteral stents in treatment of stone patients: morbidity related to indwelling times.

The morbidity and complications associated with use of internal polyurethane ureteral stents in a series of 290 stone patients treated endourologically or with extracorporeal shock wave lithotripsy were retrospectively reviewed. Of the 299 stents retrieved 141 were also tested for patency to relate the rate of luminal blockage with stent caliber, indwelling time and clinical evidence of obstruction in the stented tract. Stent indwelling times ranged from a few days to 18 months: 11.3% were indwelling longer than 6 months and 1.9% were lost to followup. Incrustation occurred in 9.2% of the stents retrieved before 6 weeks, 47.5% indwelling 6 to 12 weeks and 76.3% thereafter. In 19 cases over-all (6.4%) an auxiliary procedure was required to decrease incrusted stone burden and enable stent retrieval. Other complications included stent migration (3.7%), infection (6.7%) and breakage (0.3%). Despite a 30% rate of luminal blockage in stents retrieved after indwelling times up to 3 months, the incidence of clinical obstruction in stented tracts up to 3 months was 4%, confirming other reports that significant urine flow occurs around rather than through hollow, vented stents. Our findings underline the importance of restricting the use of stents to stone patients who will be reliable at followup. Morbidity was minimal if stent indwelling times did not exceed 6 weeks.

Catheters, Indwelling↗
PubMed2001

Severely encrusted polyurethane ureteral stents: management and analysis of potential risk factors.

OBJECTIVES: To review the management of heavily encrusted and stuck JJ ureteral stents. We report our experience and review current published reports in managing heavily encrusted and stuck JJ stents, the guidelines for management, and the prevention of such problems. METHODS: We reviewed our stent records from January 1994 to December 2000 and analyzed our stent complications and their final outcome. Fifteen patients had heavily encrusted and stuck stents. Of these, 14 were encountered in patients with a sizable stone burden (400 to 650 mm(2)) and 1 occurred in a patient with malignant ureteral obstruction. Sandwich combinations of multiple extracorporeal shock wave lithotripsy/traction and endourologic procedures were used to render them stone and stent free. The stent was examined and the encrustation was analyzed by x-ray crystallography. RESULTS: Of 15 patients, 13 were available for evaluations; 1 patient was lost to follow-up and 1 patient died. The average stone burden was 625 mm(2). The encrustation was localized to the upper end in eight and to the lower and upper end in three. In 4 cases, the entire stent was encrusted, and the lumen was occluded in 12. All 13 patients with stuck, fragmented, and encrusted stents were rendered stone and stent free; 2 of the 13 had clinically insignificant residual stones (less than 2 mm). Calcium phosphate and monohydrate stones were the most commonly encountered stone encrustations. CONCLUSIONS: Stent encrustation is one of the most serious complications of polyurethane JJ stents. Multimodal endourology should form the cornerstone of therapy for heavily encrusted stuck stents. It is important to maintain an efficient computerized stent log under the direct supervision of a physician. Patients with probable risk factors should be monitored even more frequently to avoid mishaps and morbidity.

Adult↗
PubMed2001

Lysine-derivatized polyurethane as a clot lysing surface: conversion of adsorbed plasminogen to plasmin and clot lysis in vitro.

Polyurethane surfaces to which lysine residues are immobilized by photochemical methods are proposed as a basis for clot lysing surfaces. The lysines are attached in such a way that the epsilon-amino and carboxyl groups are free. We showed previously that these surfaces, when placed in contact with plasma, adsorb only plasminogen and virtually no other proteins (McClung et al., J. Biomed. Mater. Res. 49 (2000) 409). In this communication, data based on a chromogenic substrate assay are presented showing that plasminogen adsorbed to these surfaces is readily converted to plasmin in the presence of tissue-plasminogen activator (t-PA). Moreover, the rate of activation on the surface is considerably greater than in solution. Experiments demonstrating the ability of these surfaces to dissolve fibrin clots are also reported. Surfaces exposed to plasma and then to t-PA were placed in citrated plasma. On recalcification, clotting was initiated, but the incipient clots were soon dissolved. On control surfaces (no lysine or lysine in which the epsilon-amino groups were not available) coagulation continued until a stable clot was formed. Similar observations were made when the plasma/t-PA exposed surfaces were placed in a pure fibrinogen solution and thrombin was added.

Adsorption↗
PubMed2002

(Electron) microscopic observations on tissue integration of collagen-immobilized polyurethane.

The foreign body reactions to collagen-immobilized polyurethane (PU-CI) films during subcutaneous implantation in rats were characterized. The underlying concept is that collagen-immobilization will improve the tissue integration. Since the method of collagen-immobilization involves the covalent coupling of collagen to an acrylic acid (AA) based surface graft, both non-modified PU and PU-AA were used as controls. Bare PU has a flat surface, whereas both PU-AA and PU-CI displayed a slightly roughened surface. Implantation showed that PU-CI induced early after implantation a far more intense foreign body reaction than PU and PU-AA. This reaction consisted of increased presence of fibrin, granulocytes and macrophages. Roughening of the surface as with PU-AA induced only a small increase in fibrin formation and cellular migration. At day 5 the reaction to PU-CI had slowed down; giant cell formation now slowly started but was decreased compared to PU and PU-AA. At day 10 capsules around each type of material looked similar, but in contrast to PU. PU-CI films could no longer be dissected from their capsules. Only at week 3 this also occurred with PU, at which time point again similar capsules with the three materials were observed. At week 6, of the three materials PU-CI showed the thinnest capsule with most immediate adherence of connective tissue. These results show that collagen-immobilization of PU increased the early tissue reaction and therefore the tissue integration. The thin capsule observed at 6 weeks may be beneficial in e.g. infectious circumstances, when easy access for immune reactions is needed. This, and the long-term performance of PU-CI will be a matter of future investigations.

Animals↗
PubMed2002

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties.

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate. and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR-FTIR. UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 microg/cm2 using PAS solution concentrations of 1mg/ ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic (theta(water) = 43.1 +/- 2.1) relatively to the original SPU films (theta(water) = 70.3 +/- 1.9). The in vitro albumin (BSA) adsorption shows that the PAS-SPU films adsorb more BSA (250/microgmm2) than the original SPU (112 microg mm2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.

Albumins↗
PubMed2002

Human macrophage-mediated biodegradation of polyurethanes: assessment of candidate enzyme activities.

A predominant cell type associated with explanted failed devices is the monocyte-derived macrophage (MDM). However, there is still very little known about the specific cellular enzyme activities involved in interactions with these devices. The current study investigates the nature of candidate enzymes that may be involved in the degradation of polymeric biomaterials through the use of specific enzyme inhibitor agents. When MDM were incubated with a polycarbonate-based polyurethane (PCNU) synthesized with 14C-labeled hexane diisocyanate (HDI), polycarbonate diol and butanediol (BD) (referred to as 14C-HDI431), the radiolabel release (RR) measured was inhibited by phenylmethylsulfonyl fluoride, diethyl-p-nitrophenyl phosphate (serine protease/esterase inhibitors), and sodium fluoride (NaF) (a carboxyl esterase (CXE) inhibitor). Sodium taurocholate (NaT) (a cholesterol esterase (CE) stimulator) had little effect on RR. The two candidate enzymes proposed were CE and CXE, based on the fact that both were identified by immunoblotting in the releasate of MDM following 48 h incubation with 14C-HDI431. The effect of the above reagents on the RR caused by purified CE and CXE, was measured and compared to changes in their activity with p-nitrophenylbutyrate (PNB). The effect of NaF on MDM was similar to that of purified CXE (inhibitory on both RR and lysate esterase activity), suggesting the involvement of CXE. However, NaT inhibited the PNB activity of purified CXE, but had no effect on MDM-mediated RR or PNB activity, implicating another esterase in the biomaterial degradation. Since NaT stimulated CE-mediated RR and PNB activity, it may also be involved in MDM-mediated biodegradation of PCNUs. The results of these studies point to both esterases as being candidates. However, the current methods were unable to determine the relative contribution of each one to the observed biodegradation.

Biocompatible Materials↗
PubMed2002

Assessment of PEO/PTMO multiblock copolymer/segmented polyurethane blends as coating materials for urinary catheters: in vitro bacterial adhesion and encrustation behavior.

The effective long-term use of indwelling urinary catheters has often been hindered by catheter-associated infection and encrustation. In this study, the suitability of poly(ethylene oxide) (PEO)-based multiblock copolymer/segmented polyurethane (SPU) blends as coating materials for the commercial urinary catheters was assessed by measuring swellability, bacterial adhesion, and encrustation behavior. When exposed to PBS (pH 7.4), the blends absorbed a significant amount of water, which was proportional to the copolymer content. It was demonstrated from bacterial adhesion tests that compared to bare SPU, the blend surfaces could significantly reduce the adhesion of E. coli, P. mirabilis, and S. epidermidis; the number of adherent bacteria correlated with the amount of copolymer additive. indicating that the swellability of the blends affected bacterial adhesion. Of the bacteria studied, the greatest effect of the copolymer additive was observed in S. epidermidis adhesion, in which there was an 85% decrease compared to bare SPU with a small amount of copolymer additive as low as 5% based on a dried blend. By using an artificial bladder model, allowing the catheter to be blocked by encrustation, it was revealed that the blend surfaces could effectively resist encrustation. The duration of patency was extended up to 20 +/- 3.1 h on the blend surface containing 10% of the copolymer additive, whereas the silicone-coated catheter, a control, required the least time for blockage, 7.8 +/- 3.1 h. The superior characteristics of the blends compared to other surfaces might be attributed to their PEO-rich surfaces, produced by the migration of PEO phase in the copolymer chain of the blends in an aqueous environment, and provide promising potential as a coating material on the urinary catheter for long-term catheterization.

Bacterial Adhesion↗
PubMed2002

Physical properties and blood compatibility of surface-modified segmented polyurethane by semi-interpenetrating polymer networks with a phospholipid polymer.

Segmented polyurethanes, (SPU)s, are widely used in the biomedical fields because of their excellent mechanical property. However, when blood is in contact with the SPU, non-specific biofouling on the SPU occurs which reduces its mechanical property. To obtain novel blood compatible elastomers, the surface of the SPU was modified with 2-methacryloyloxyethyl phosphorylcholine (MPC) by forming a semi-interpenetrating polymer network (semi-IPN). The SPU film modified by MPC polymer with the semi-IPN (MS-IPN film) was prepared by visible light irradiation of the SPU film in which the monomers were diffused. X-ray photoelectron spectroscopy confirmed that the MPC units were exposed on the MS-IPN film surface. The mechanical properties of the MS-IPN film characterized by tensile testing were similar to those of the SPU film. Platelet adhesion on MS-IPN films was also investigated before and after stress loading to determine the effects of the surface modification on the blood compatibility. Many platelets did adhere on the SPU film before and after stress loading. On the other hand, the MS-IPN film prevented platelet adhesion even after repeated stress loading.

Blood Platelets↗