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PubMed1993

Studies on thio-substituted polyurethane foam (T-PUF) as a new efficient separation medium for the removal of inorganic/organic mercury from industrial effluents and solid wastes.

Novel thio-substituted flexible polyurethane foam (T-PUF) was synthesised by addition polymerisation of mercaptan with the precursors of an open-cell polyurethane foam, which can be used as a highly selective sorbent for inorganic and organic mercury from complex matrices. The percentage extraction of inorganic mercury was studied at different flow-rates, over a wide pH range at different concentrations ranging from 1 ppm, to 100 ppm. The break-through capacity and total capacity of unmodified and thio-foams were determined for inorganic and organic mercurials. The absorption efficiency of thio-foam was far superior to other sorbent media, such as activated carbon, polymeric ion-exchange resins and reagent-loaded polyurethane foams. It was observed that even at the 1000 ppm level, divalent ions like Cu, Mg, Ca, Zn do not appreciably influence the per cent extraction of inorganic mercury at the 10 ppm level. These matrix levels are the most concentrated ones which are likely to occur, both in local sewage and effluent waters. Further, the efficiency of this foam was sufficiently high at 10-100 ppm levels of Hg, even from 5-10 litres of effluent volumes using 50 g of thio-foam packed into different columns in series. Thio-foams were found to possess excellent abilities to remove and recover mercury even at low levels from industrial effluents and brine mud of chlor-alkali industry after pre-acid extraction. This makes it a highly efficient sorbent for possible application in effluent treatment. Model schemes for the removal and recovery of mercury from industrial effluents and municipal sewage (100-1000 litre) by a dynamic method are proposed and the costs incurred in a full-scale application method are indicated to show that the use of thio-foam could be commercially attractive.

Journal Article↗

PubMed2005

Uncatalyzed synthesis, thermal and mechanical properties of polyurethanes based on poly(epsilon-caprolactone) and 1,4-butane diisocyanate with uniform hard segment.

Polyurethanes based on poly(epsilon-caprolactone) (PCL) (750-2800 g/mol) and 1,4-butane diisocyanate (BDI) with different soft segment lengths and constant uniform hard segment length were synthesized in absence of catalysts for the production of a degradable meniscus scaffold. First the polyesterdiols were endcapped with BDI yielding a macrodiisocyanate with a minimal amount of side reactions and a functionality of 2.0. Subsequently, the macrodiisocyanates were extended with 1,4-butanediol in order to obtain the corresponding polyurethane. The polyurethanes had molecular weights between 78 and 160 kg/mol. Above molar masses of 1900 g/mol of the polyesterdiol crystalline PCL was found while the hard segment showed an increase in melting point from 78 to 122 degrees C with increasing hard segment content. It was estimated that the percentage crystallinity of the hard segment varied between 92 and 26%. The Young's modulus varied between 30 and 264 MPa, the strain at break varied between 870 and 1200% and tear strengths varied between 97 and 237 kJ/m2.

Absorbable Implants↗

PubMed2005

Preparation and characterization of high-specific-surface-area activated carbons from K2CO3-treated waste polyurethane.

An activated carbon with high specific surface area was prepared from polyurethane foam by chemical activation with K2CO3 and the influences of carbonization temperature and impregnation ratio on the pore structure of the prepared activated carbon were investigated. It was found that the specific surface area of the activated carbon was at a maximum value (about 2800 m(2)/g) at a carbonization temperature of 1073 K and at an impregnation ratio of 1.0. It was concluded that the polyurethane foam structure was modified during impregnation by K2CO3, K2CO3 promoted charring during carbonization, and then the weight loss behavior was changed below 700 and above 1000 K, carbon in the char was consumed by K2CO3 reduction, and this led to the high specific surface area. The prepared activated carbon had a very sharp micropore size distribution, compared with the commercial activated carbon having high specific surface area. The amounts of three organic vapors (benzene, acetone, and octane) adsorbed on the prepared activated carbons was much larger than those on the traditional coconut shell AC and the same as those on the commercial activated carbon except for octane. We surmised that the high specific surface area was due to the modification of the carbonization behavior of polyurethane foam by K2CO3.

Journal Article↗

PubMed2006

AFM study of forces between silica, silicon nitride and polyurethane pads.

Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical-mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.

Journal Article↗

PubMed2000

Characterization of PCB-degrading bacteria immobilized in polyurethane foam.

This study is carried out to investigate (1) conditions for the synthesis of polyurethane foam to be used for immobilizing microorganisms, (2) the viability of microorganisms immobilized simultaneously into the pores of a polyurethane foam when the foam is synthesized, and (3) the difference in the ability to degrade PCBs between the immobilized and suspended microorganisms. The results of this study show that polyurethane foam is suitable for synthesizing 10% NCO-prepolymer, water and surfactant in the ratio of 100:2.6:1.2 (w/w), respectively, and the viability of microorganisms (input microbes) immobilized in the foam is high. The input microbes, designated as strain SY5, are isolated from a municipal sewage treatment plant. In addition, immobilized strain SY5 degrades 5-40% more PCB of a PCB mixture (Aroclor 1242) than the suspended strain SY5.

Journal Article↗

PubMed2002

Nonporous polyurethane membranes as islet immunoisolation matrices--biocompatibility studies.

Novel elastomeric nonporous polyurethane membranes were synthesised with differing hard segment contents for evaluation as possible islet encapsulation matrices. Physico-chemical properties of these membranes were reported earlier by authors and have been found suitable for immunoisolation. In the present study, membranes were evaluated for their in vitro biocompatibility. Membranes T1, T4, T5 and T6 did not show toxicity in direct cell contact study towards L929 fibroblasts. However, T2 and T3 were found cytotoxic and were excluded from further testing. NIH3T3 cells when exposed to leach out products of T4, T5 and T6 showed no cytotoxicity, while T1 decreased cellular viability as confirmed by MTT assay. T4 and T5 alone were seen to be compatible with mouse islets while T6 was incompatible to the mouse islets. Digital image analysis (DIA) studies showed intact morphology of islets cultured on the T4 and T5 with viability (88.4 and 91% respectively) comparable to islets on tissue culture polystyrene (TCPS) control. Islets on T4 and T5 also retained their functionality, as judged by insulin secretion in response to in vitro glucose challenge (16.0 mM). These studies point out the crucial role of surface free energy and hydrophilicity in deciding compatibility of polyurethane membranes with islets of Langerhans. Studies indicate that polyurethane membranes T4 and T5 could be potential candidates for islet immunoisolation.

3T3 Cells↗

PubMed1995

Nonsurgical placement of a nasolacrimal polyurethane stent.

PURPOSE: To describe the placement of a nasolacrimal polyurethane stent with a new introducer set and hook. MATERIALS AND METHODS: The authors designed a soft polyurethane stent, an introducer that does not require balloon dilation, and a hook that can remove a ball-tipped guide wire from the inferior nasal meatus under fluoroscopic guidance. The stent was placed in 51 lacrimal systems in 44 outpatients who had complete obstruction of the lacrimal sac or nasolacrimal duct. RESULTS: Stent placement was technically successful and well tolerated in 50 of 51 nasolacrimal systems. The procedure lasted an average of 16 minutes (range, 10-33 minutes). After stent placement, 47 of 50 eyes showed complete resolution of epiphora, and the other three showed partial resolution. During follow-up, no stents migrated, and one stent became blocked. The stent was reopened by means of forceful irrigation of saline solution through the superior punctum. CONCLUSION: Placing a polyurethane nasolacrimal stent by use of the new introducer and hook simplifies the technique, shortens operating time, reduces cost, and makes the procedure well tolerated by patients.

Adolescent↗

PubMed2002

In vitro hydrodynamics of a decellularized pulmonary porcine valve, compared with a glutaraldehyde and polyurethane heart valve.

BACKGROUND: Hydrodynamic performance of a decellularized pulmonary porcine valve was evaluated with a computer versatile pulse duplicator and compared to glutaraldehyde fixated stentless porcine bioprosthesis and a polyurethane heart valve. METHODS: Decellularized pulmonary porcine matrices (Group I, n = 5) were treated chemically to become cell-free collagen matrices. The findings of this heart valve were compared with aortic glutaraldehyde treated porcine prostheses (Group II, n = 5) and polyurethane three leaflet valve prostheses (Group III, n = 1). Measurements were performed in 0.9% saline test fluid at room temperature. Measurements compared were closing time, closing volume, systemic pressure difference and energy losses. Each valve was measured 6 times with 70 beats/minute, a stroke volume of 70 ml corresponds to a cardiac output of 4.9 L/minute. RESULTS: Group I and group III showed no significant differences between parameters. The measured closing time was significantly different (p < 0.001) between group I and II, respectively 24.333 and 53.600 ms and group II and III respectively 53.600 and 24.000. Difference in closing volume was significant (p < 0.05) between groups II and I respectively 3.67 and 0.68 ms and group II and III respectively 3.67 and 0.71. Systolic mean pressure gradient was 18.25 +/- 1.04 mm Hg in group II which was significantly different (p < 0.001) from groups I and III, respectively 10.65 +/- 0.29 mm Hg and 7.70 +/- 0.30 mm Hg. CONCLUSIONS: Decellularized pulmonary porcine valves showed the same excellent performance as polyurethane valve prosthesis, which are superior to the investigated glutaraldehyde fixed xenograft.

Animals↗

PubMed1999

[n]-Polyurethanes: Synthesis and Characterization.

More than 50 years after Otto Bayer's detailed description of [m,n]-polyurethanes, the first general synthesis of [n]-polyurethanes 1 is described. This series of aliphatic [n]-polyurethanes is synthesized by the in situ polymerization of the corresponding alpha,omega-isocyanato alcohol monomers, which in turn are made out of linear alpha,omega-amino alcohols and di-tert-butyltricarbonate. Polymers of high molecular weight possessing a uniform microstructure are obtained, while their melting points show a strong odd-even effect.

Journal Article↗

PubMed2004

[Polyurethane vessels for microvascular surgical training to reduce animal use].

AIM: Systematic training of the manual skills is inevitable in learning microsurgery. Generally, first exercises are done on two-dimensional models, then the training continues on animals. With the growing ethical awareness, the obligation to protect animals and the stricter animal protection laws, realistic three-dimensional models have become necessary for training of microsurgery. However, the available alternatives all have certain disadvantages. We tested vessels made of polyurethane for microvascular surgical training and compared them to the available three-dimensional synthetic alternatives. DESCRIPTION OF THE TRAINING MODEL: Rose-coloured (arteries) or blue (veins), opaque vessels with a minimal wall thickness of 0.12 mm and a minimal internal diameter of 1 mm are used. To mimic the surgical access and the depth of the operative field, the vessels can be embedded in a synthetic box with or without a cap. The completed anastomosis is checked by injection of a coloured fluid. EXPERIENCES: The consistency and the variable relation of the thickness of the wall to the internal diameter very closely reflect the biological situation. Even training on very fragile venous walls is possible in all manners. After completion of anastomosis the vessels can be opened longitudinally to check the patency of the anastomotic site. DISCUSSION: The described polyurethane vessels are very suitable for microsurgical training as a useful step between the two-dimensional model and the animal. The number of animals required for microsurgical training can clearly be reduced by the use of such synthetic polyurethane vessels.

Anastomosis, Surgical↗

PubMed1977

Polyurethane foam (Bentley) micropore blood transfusion filter: filtration characteristics.

Stored human blood of varying age was passed through polyurethane foam (Bentley) micropore blood transfusion filters. Passage through these filters resulted in decreased screen filtration pressure (SFP) of the blood and increased filter weights. Numerous microaggregates were removed and SFP returned to normal after filtration. Occlusion of the filter occurred after passage of only 2 units of whole blood. On the basis of this research, we conclude that polyurethane foam (Bentley) micropore blood transfusion filters are effective in removal of microaggregates from stored human blood. Because the filtering capacity is not great, it is recommended that when these filters are used during transfusion a new filter be used for each unit of blood administered.

Blood Preservation↗

PubMed1997

Physicochemical properties and platelet interactions of segmented polyurethanes containing sulfonate groups in the hard segment.

The adhesion of platelets to a series of segmented polyurethanes having sulfonate groups in the hard segment is reported. The polyurethanes were synthesized using sulfonated chain extenders of different structure. Analogous control materials without sulfonate groups also were studied. Adhesion was measured in vitro using washed human platelets in a carrier fluid consisting of Tyrode's buffer with apyrase, albumin, and red cells at normal concentration. The polymers were characterized by gel permeation chromatography and elemental analysis. Water absorption and thermal transitions also were determined. It was found that the sulfonated materials absorb significant amounts of water while the nonsulfonated analogs do not. The surfaces of polymer films were characterized by water contact angle and XPS. The contact angles of the sulfonated surfaces were relatively low. Platelet adhesion to the sulfonated polymers was found to be very high compared to the nonsulfonate analogs. The local environment of the sulfonate groups (different chain extenders) also appears to have an effect on platelet interactions. Albumin adsorption was high on all the materials and was not correlated with platelet adhesion. It appears from this work that platelets may have a binding site that is specific for sulfonate groups.

Adsorption↗

PubMed1997

Chronology of alveolar healing following immediate implantation of Ricinus communis polyurethane resin: histometric analysis in rats.

The purpose of the present study was to determine whether granules of Ricinus communis polyurethane resin implanted immediately after tooth extraction interfere with the time course of alveolar wound healing in rats. Progressive bone neoformation in parallel to a decrease in the volume fraction of connective tissue was quantified by a histometric method 1, 2, 3, and 6 weeks after tooth extraction. In spite of the biocompatible nature, the presence of polyurethane resin granules in the cervical third led to a small (9-22%) but significant delay in bone formation in the middle and apical alveolar thirds from the second week on, as compared to controls.

Alveolar Process↗

PubMed2001

Enzyme-induced biodegradation of polycarbonate-polyurethanes: dependence on hard-segment chemistry.

Polycarbonate urethanes (PCNUs) have been used as a replacement for traditional biomedical polyether-urethanes due to their reported resistance to oxidative biodegradation. However, relatively little is known about their hydrolytic stability in the presence of inflammatory derived enzymes. This has in part motivated the current study relating to the effect of hard segment chemistry and the microdomain structures generated by such chemistry, on the cholesterol esterase (CE) catalyzed hydrolysis of PCNUs. The bulk structures of the studied materials were characterized using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR) for their bulk structures, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for their subsurface structures. 14C-labeled PCNUs were incubated with CE (400 units/mL), for a period of 10 weeks (pH 7.0 at 37 degrees C), and radiolabel release was used to monitor the degradation. The results showed that all of the polymers synthesized in this study were susceptible to CE-catalyzed hydrolytic degradation, and that the extent of degradation was highly dependent on the nature of hard segment interactions within the polymer and at the surface. More specifically, the degree of phase separation and soft segment crystallinity were found to be less important in comparison to the hydrogen bonding among the carbonate and urethane linkages. The rank of the different chemical groups' susceptibility to hydrolysis was as follows: nonhydrogen bonded carbonate > nonhydrogen bonded urethane > hydrogen bonded carbonate > hydrogen bonded urethane. The findings suggest that the degree of hydrogen bonding, when processed into a polyurethane material could be an important parameter to consider in the design of new biostable polyurethane products.

Biocompatible Materials↗

PubMed2007

Polyurethane elastomer: a new material for the visualization of cadaveric blood vessels.

A multitude of various materials are available for the visualization of cadaveric vessels, ranging from natural materials like gelatin and latex to synthetic materials like silicone rubber or acrylates. To achieve a detailed overview of the vascular architecture in microvascular studies in experimental flap surgery, the injected material should have low viscosity to assure perfusion of even the smallest vessels. In addition, the material ideally should have either no or only minimal shrinkage, and should harden within a reasonable time, but retain sufficient elasticity and resistance to withstand tearing off the delicate vessels during subsequent dissection or casting. Because none of the available injection materials adequately combines these attributes, we evaluated the polyurethane elastomer "PU4ii" in latissimus dorsi muscles as a new material for the visualization of cadaveric vessels in comparison with the frequently used silicone rubber. The dissection of vessels injected with PU4ii proved easy largely because of its exceptional hardness. Even if not visible before dissection, the completely perfused vessels were easily palpated in the surrounding fat or muscle tissue of the microsurgical latissimus dorsi model. Despite the significantly higher hardness of PU4ii over silicone rubber (98 Sh-A vs. 12 Sh-A), PU4ii proved enough elasticity (20-25 N/mm(2) E modulus) and a high tear resistance (64-68 N/mm vs. 15 N/mm) preventing breakage during dissection even within the smallest vessels. In contrast to silicone rubber (and latex or gelatin), the high corrosion resistance and form stability of PU4ii also allowed building of casts for qualitative examination by scanning electron microscopy and quantitative analysis of the vessel density using micro-computed tomography with accurate 3D representation. In this study we show that PU4ii has physical characteristics that make it a multi-purpose material that allows at the same breath an excellent gross visualization of the architecture of cadaveric blood vessels as well as a detailed evaluation of casts by modern microscopic and or radiologic tools. Thus, the new polyurethane elastomer PU4ii is in many respects superior to the widely used silicone rubber and can be strongly recommended as a visualization material for a comprehensive evaluation of cadaveric blood vessels in microsurgery.

Aged↗

PubMed1993

Porous polyurethane tubes as vascular graft.

A vascular graft with the inner diameter of about 3 mm was prepared from segmented poly (ether urethane) with an extrusion technique. To make the wall of the vascular grafts porous, NaCl salts were added to the polyurethane solution to be extruded and removed with water extraction after evaporating the solvent in the extruded tube. The wall was reinforced with elastic fiber to prevent dilation. The compliance of the vascular graft measured with the method of Hayashi et al. ranged from 0.2 to 0.3% mmHg -1. The initial Young's modulus was close to that of canine carotic artery, to which the porous polyurethane graft 4-cm long was anastomosed. Vascular grafts were occluded within 2 weeks after implantation, when their pore size was 0, 1.7, or 4.4 mum, whereas those with the pore size of 5.5, 7.4, and 30 mum were patent for longer than 4 weeks. When the vascular graft with the pore size of 30 mum was implanted for 6 months, the luminal surface was covered with neointima, but the endothelium-like cells appearing in the middle of the intima of the vascular graft were immature and sometimes had a very big nucleus. In addition, spindle-shaped, modified smooth muscle cells were noticed in the deep layer of the neointima, especially in the tissue where anastomotic intimal hyperplasia occurred.

Animals↗

PubMed2002

Mechanical and morphological study of biostable polyurethane heart valve leaflets explanted from sheep.

Two novel biostable polyurethanes, designated EV3.34 and EV3.35, were used to manufacture a flexible trileaflet heart valve. The valves were implanted in the mitral position in young adult (18 month) sheep. Six valves were electively explanted at 6 months and the remaining six valves at 9 months follow-up. The leaflet material was examined by surface Fourier transform infrared spectrometry (ATR/FTIR) and scanning electron microscopy (SEM). The leaflet material was also subjected to cyclic mechanical testing and, compared with unimplanted control material, to demonstrate any change in mechanical properties during implantation. There was no degradation of functional groups detected by ATR/FTIR, although there was a slight surface enrichment of siloxane soft segment. Surface morphology of the explanted leaflet material was similar to unimplanted control material. EV3.34 demonstrated similar inelastic energy loss behavior, with no significant change in residual strain in explanted compared with control material. EV3.35 demonstrated a reduction in inelastic energy and residual strain in explanted compared with control material. There is no evidence of biodegradation of these siloxane-based polyurethanes, in functional valves up to 9 months implantation in sheep. The FTIR and SEM findings are supported by the retention of mechanical properties of the materials.

Animals↗

PubMed1977

Interactions between segmented polyurethane surfaces and the plasma protein fibrinogen.

Surfaces of a segmented polyurethane were varied by casting on poly(ethylene terephthalate) (PET) and glass substrates, and were characterized through infrared-attenuated total-reflection spectroscopy (ATR). Surfaces cast on glass substrates showed a higher content of polyether segments, whereas those cast on PET contained a higher relative concentration of aromatic segments. Adsorption, and possible conformational changes of fibrinogen, were found to be more substantial on polymer surfaces having a higher content of polyether segments. It is concluded that the relatively good blood compatibility of segmented polyurethanes is partly due to the presence of peptide-like bonds on aromatic segments.

Adsorption↗