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At least 1,675 records · Page 93Linked to original sources
PubMed2006

Preparation of holographic gratings of liquid crystals dispersed in polyurethane acrylates under controlled reaction conditions.

Transmission gratings of holographic polymer-dispersed liquid crystals (HPDLC) are prepared under controlled reaction conditions by adding various amounts of chain-transfer agent (CTA). The resulting films have a higher gel content with lower cross-link density, less dark reaction, less grating shrinkage with much smoother LC/polymer interfaces, smaller induction period, and fast saturation of diffraction efficiency, which shows a maximum of 95 % with 1 % CTA. An optimum LC content of 35 % is verified on the basis of morphology and reaction kinetics.

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PubMed2007

Surfactant effects on morphology and switching of holographic PDLCs based on polyurethane acrylates.

Effects of octanoic acid (OA) on the morphology, diffraction efficiency, and electro-optic properties of the transmission mode of holographic polymer-dispersed liquid crystals (HPDLC) are studied. Droplet size decreases with increasing OA content (0-9 %), and this leads to a monotonic increase in off-state diffraction with increasing OA content. However, on-state diffraction decreases with increasing applied voltage and shows a minimum at 6 % OA, for which minimum switching voltage (5 V microm(-1)) and maximum contrast ratio (10) are obtained. Rise time and decay time decrease with increasing OA content. Interposition of OA between polymer and LC droplet is theoretically predicted by the spreading coefficient (lambda>0) calculated on the basis of the solubility parameter, while the coalescence behavior of droplets is described by a dimensionless group (gamma d rho / mu(2)) called coalescence number.

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PubMed1997

Pericardial parenteral nutrition infusion following acute angulation of a neonatal polyurethane central venous catheter tip.

Life threatening cardiac tamponade developed in a premature infant due to perforation of the heart by a 2F central venous catheter used to administer parenteral nutrition. Abnormal orientation of the catheter tip preceded the appearance of the pericardial effusion. Unusual angulation of the tip of central venous lines in premature infants may be an important warning sign of impending cardiac perforation and its potentially major sequelae and should therefore prompt immediate repositioning of the catheter.

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PubMed2000

New non-woven polyurethane-based biomaterials for the cultivation of hepatocytes: expression of differentiated functions.

A new non-woven polyetherurethane support suitable to host cultured hepatocytes has been developed. Prior to its use in bioreactors and artificial liver devices, the biocompatibility of this new material was investigated. The experiments have shown that the survival and functionality of hepatocytes entrapped in the non-woven polymer were longer than that of monolayer cultured hepatocytes, under serum-free culture conditions. Hepatic specific metabolic functions, namely, synthesis of urea and synthesis and secretion of plasma proteins, were well maintained by hepatocytes entrapped in non-woven polyetherurethane sheets. Cells also retained the expression of biotransformation activities of 7-ethoxycoumarin-O-deethylase as well as CYP2A1, CYP2B1 and CYP3A1. The results presented in this paper point to non-woven polyetherurethane sheets as a suitable biocompatible support for functional, three-dimensional hepatocyte cultures.

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PubMed2002

Studies of polyurethane urea bands for ACL reconstruction.

The present report describes the mechanical tests, in vitro and in vivo studies of a poly(urethane urea) (PUUR) intended for clinical use in anterior cruciate ligament (ACL) reconstruction. In the mechanical tests, no evidence of severe fatigue was observed after repeated cyclic loading. Testings for mutagenicity and delayed contact hypersensitivity were found negative. Three in vivo studies were performed in rabbits and minipigs. Altogether 35 rabbits were operated upon in (1) an intraarticular implantation study, performed to evaluate the soft tissue response to woven bands and fiber bundles of PUUR and (2) a rabbit ACL study, examining the function of the PUUR ACL replacement and the tissue response to the material. In a third study, PUUR ACL replacement in minipigs was evaluated. Taken together, ingrowth of connective tissue in close contact with the PUUR fibers was detected both in rabbits and minipigs. The first clear histological signs of degradation of the polymer was detected after 24 months. In conclusion, the evaluated mechanical properties of the PUUR band correspond to those of the mature, human ACL. Furthermore, both from a histological and functional point of view, the PUUR woven band show interesting properties for future clinical ACL reconstructions.

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PubMed2002

Hyaluronic acid and silver sulfadiazine-impregnated polyurethane foams for wound dressing application.

Five different kinds of PU foam wound dressings were prepared to investigate their wound healing capability. They include (i) PU+silver sulfadiazine (AgSD), (ii) PU+alginate (Al), (iii) PU+Al+AgSD, (i.v.) PU+hyaluronic acid (HA), and (v) PU+HA+AgSD. Physical properties and in vitro behaviors of AgSD release and fibroblast adhesion on those dressings were evaluated. From the drug release and fibroblast adhesion studies, it was observed that PU foam impregnated with both HA and AgSD shows good drug release behavior and low adhesion of the cells. Furthermore, the HA and AgSD-containing PU foam showed excellent wound healing effect without any inflammation or yellow cluster. The wound size decreased around 77% after 1 week application of that foam dressing onto a rat skin defect.

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PubMed1997

Reduced airway resistance and work of breathing during mechanical ventilation with an ultra-thin, two-stage polyurethane endotracheal tube (the Kolobow tube).

OBJECTIVES: To compare dynamic pulmonary function studies using the ultrathin walled Kolobow endotracheal tube, with conventional endotracheal tubes of similar external diameter on rabbits during mechanical ventilation. To test the hypothesis that the increased internal diameter of the Kolobow tube will result in decreased airway resistance and work of breathing. DESIGN: Controlled animal study. SETTING: Institutional animal research facility. SUBJECTS: Adult female Dutch Belted rabbits (n = 6), weighing 1.4 to 1.6 kg. INTERVENTIONS: The animals were initially intubated with a conventional endotracheal tube (2.5-mm internal diameter; 3.6-mm outer diameter); they were paralyzed and placed on a mechanical ventilator. Ventilatory settings were adjusted to obtain standard arterial blood gases: pH of 7.35 to 7.45; PaCO2 of 35 to 40 torr (4.7 to 5.3 kPa), and PaO2 of 90 to 100 torr (12.0 to 13.3 kPa). After the stabilization period, pulmonary function tests (PFTs) were measured (period 1), the conventional endotracheal tube was replaced with a Kolobow tube, and PFTs were measured again and recorded (period 2). While continuously monitoring tidal volume, the peak inspiratory pressure was decreased to match the tidal volume measured during ventilation with the conventional endotracheal tube. Once the desired tidal volume was reached, PFTs were recorded (period 3). Flows were unchanged during the experiment and the length of the endotracheal tubes was the same for both the conventional and the Kolobow tube. MEASUREMENTS AND MAIN RESULTS: Mean values of the airway resistance and work of breathing from periods 1 and 3 were compared using the Student's t-test. There was a 59% decrease in total airway resistance (p = .001) and 45% decrease in the work of breathing (p = .0006). CONCLUSIONS: The use of the ultrathin walled Kolobow endotracheal tube resulted in significant decreases in airway resistance and work of breathing, which has the potential for improving the ventilatory mechanics in very small premature newborns.

Airway Resistance↗