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At least 163 records · Page 9Linked to original sources
PubMed2002

Incoherent neutron scattering and the dynamics of confined polycarbonate films.

Incoherent elastic neutron scattering measurements are performed on thin (75 to 1015 A) polycarbonate films supported on Si wafers. We find that the mean-square atomic displacement is diminished by thin film confinement. For film thicknesses comparable to the unperturbed dimensions of the macromolecule, we observe two characteristic crossover temperatures in as a function of temperature T, one above and the other below the bulk T(g). Furthermore, the harmonic force constant kappa, defined by the low temperature dependence of (i.e., kappa approximately k(B)T/ ), increases as the film thickness decreases. These observations suggest that the atoms are more strongly localized in the thin supported films.

Journal Article↗
PubMed2003

Dimensional stability and dehydration of a thermoplastic polycarbonate-based and two PMMA-based denture resins.

This study compared the dimensional stability and dehydration of a thermoplastic polycarbonate denture base resin with two conventional polymethyl methacrylate denture base resins. Maxillary complete dentures were fabricated from the three denture materials and the accuracy of fit along the posterior palatal border of the cast used in processing was measured. Measurements were conducted at five palatal locations immediately after processing and at 7 and 30 days during immersion in water (23 degrees C) and at 7 and 30 days during dehydration (23 degrees C, 65-75% relative humidity). Percentage mass loss during dehydration was determined with an electronic balance. The thermoplastic material was separately compared with each of the conventional resins using a modified Welch two-sample t-test, with a Bonferroni correction for P values. For mean palatal dimensional change, the thermoplastic resin was generally not statistically different from the conventional resins after processing and during immersion (P > or = 0.06), but was generally less than the conventional resins during dehydration (P < or = 0.02). For mean percentage mass loss, the thermoplastic resin consistently showed much smaller, statistically significant values compared with the conventional resins (P < 0.001). It was concluded that the thermoplastic resin should show dimensional changes in service comparable with the conventional resins, but less dimensional change caused by dehydration.

Acrylic Resins↗
PubMed1998

Bacterial isolates degrading aliphatic polycarbonates.

Bacteria that degrade an aliphatic polycarbonate, poly(hexamethylene carbonate), were isolated from river water in Ibaraki. Prefecture, Japan, after enrichment in liquid medium containing poly(hexamethylene carbonate) suspensions as carbon source, and dilution to single cells. Four of the strains, 35L, WFF52, 61A and 61B2, degraded poly(hexamethylene carbonate) on agar plate containing suspended poly(hexamethylene carbonate). Degradation of poly(hexamethylene carbonate) was confirmed by gel permeation chromatography. Besides poly(hexamethylene carbonate), the strains were found to degrade poly(tetramethylene carbonate). The strains were characterized morphologically, physiologically, and by 16S rDNA sequence analysis. Strains 35L and WFF52 were tentatively identified as Pseudomonas sp. and Variovorax sp., respectively, while strains 61A and 61B2 constitute an unidentified branch within the beta subclass of the Proteobacteria.

Bacteria↗
PubMed1993

Oral sustained-release drug delivery systems using polycarbonate microspheres capable of floating on the gastric fluid.

Polycarbonate microspheres loaded with aspirin, griseofulvin and p-nitroaniline were prepared by a solvent evaporation technique. High drug loading (> 50%) was achieved by this process. Drug-loaded microspheres were found to float on simulated gastric fluid and intestinal fluid. Drug-release studies were carried out in these fluids at 37 degrees C. Increasing the drug to polymer ratio in the microspheres increased both their mean particle size and the release rate of the drugs. It was concluded that sustained delivery of drugs could be effected using this matrix.

Aniline Compounds↗
PubMed1989

Comparison of a new inorganic membrane filter (Anopore) with a track-etched polycarbonate membrane filter (Nuclepore) for direct counting of bacteria.

Bacterial counts obtained by using a new Anopore inorganic membrane filter were 21 to 33% higher than those obtained by using a Nuclepore polycarbonate membrane filter. In addition, the inorganic filter had higher flow rates, permitting lower vacuum pressures to be used, while the intrinsically flat, rigid surface resulted in easier focusing and sharp definition of bacteria across the whole field of view.

Bacteriological Techniques↗
PubMed1997

Growth of silicone-immobilized bacteria on polycarbonate membrane filters, a technique to study microcolony formation under anaerobic conditions.

A technique was developed to study microcolony formation by silicone-immobilized bacteria on polycarbonate membrane filters under anaerobic conditions. A sudden shift to anaerobiosis was obtained by submerging the filters in medium which was depleted for oxygen by a pure culture of bacteria. The technique was used to demonstrate that preinduction of nitrate reductase under low-oxygen conditions was necessary for nonfermenting, nitrate-respiring bacteria, e.g., Pseudomonas spp., to cope with a sudden lack of oxygen. In contrast, nitrate-respiring, fermenting bacteria, e.g., Bacillus and Escherichia spp., formed microcolonies under anaerobic conditions with or without the presence of nitrate and irrespective of aerobic or anaerobic preculture conditions.

Anaerobiosis↗
PubMed2003

Germination and adhesion of fungal conidia on polycarbonate membranes and on apple fruit exposed to mycoactive acetate esters.

The adhesion and germination of conidia of nine fungal species were assessed on polycarbonate membranes or on the skin of apple fruit in sealed glass bottles injected or not injected with acetate esters. Adhesion was determined after dislodging conidia from surfaces using a sonication probe. Adhesion and germination of conidia of Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Penicillium citrinum, Penicillium claviforme, or Trichoderma sp. on membranes after 48 h were not increased in a 1.84 microg mL(-1) headspace of butyl acetate (BA), ethyl acetate, hexyl acetate, 2-methylbutyl acetate, pentyl acetate, or propyl acetate. Adhesion and germination of Botrytis cinerea, Penicillium expansum, and Penicillium roquefortii conidia were stimulated by all esters. Only conidia of B. cinerea and P. expansum exhibited increased adhesion and germination on the skin of apple fruit in bottles exposed to 0.92 microg mL(-1) of BA. Only conidia of B. cinerea and P. expansum produced decay in inoculated puncture wounds on fruit. Freshly made puncture wounds or 24-h-old puncture wounds in fruit were more adhesive than the unpunctured skin of fruit to conidia of B. cinerea or P. expansum. Fresh wounds were more adhesive to both fungi than 24-h-old puncture wounds. The skin and wounds of fruit were as adhesive to B. cinerea conidia as they were to P. expansum conidia. A 4-h exposure to 1.43 microg mL(-1) of BA increased adhesion of B. cinerea and P. expansum conidia in 24-h-old wounds. Results suggest that acetate-ester stimulation most likely is not a rare phenomenon in the fungi. For nutrient-dependent decay pathogens of apple fruit, acetate esters may be an alternative chemical cue used to maintain adhesion of conidia to wound surfaces.

Acetates↗
PubMed1986

Polycarbonate-polyether (PC-PE) flat sheet membrane: manufacture, structure and performance.

Polycarbonate-polyether (PC-PE) polymer, prepared by solution or interfacial polymerization, was used to produce a dry PC-PE diffusion membrane by means of the phase inversion technique. The mechanical stabilities and diffusive permeabilities of chloride, phosphate and vitamin B12 were determined for this membrane. Additionally, close control over manufacturing parameters allowed the study of the effects of varied membrane thickness (at constant ultrafiltration rate) and varied ultrafiltration rate (at constant membrane thickness) on solute diffusive permeabilities. Both increased ultrafiltration rate and decreased thickness resulted in an increase in solute diffusive permeabilities.

Humans↗
PubMed1986

In vivo analysis of the Lundia 5 (PRO 5) and Lundia 3 (PRO 3) dialyzers with Gambrane polycarbonate membranes.

The physical, solute transfer and biocompatibility properties of two new parallel plate dialyzers using Gambrane polycarbonate (PC) membrane of 0.8 m2 (L-3 PC) and 1.1 m2 (L-5 PC) were studied in 6 volunteer chronic dialysis patients. Two of these 6 had suffered severe first-use syndromes with Cuprophan. Samples were collected under carefully controlled conditions. Mass transport properties were confirmed by total dialysate collection and found to compare favorably with other standard dialyzers. For the L-3 PC, KUF was 3.59 ml/h/mm Hg TMP-14.5 and standard whole blood clearances were BUN 142, creatinine 121 and inorganic phosphate 69 ml/min. For the L-5 PC, KUF was 6.27 ml/h/mm Hg TMP-28.66 and standard clearances were BUN 155, creatinine 134 and inorganic phosphate 89 ml/min. Using bicarbonate dialysate no consistent hypoxemia occurred and all dialyses were well tolerated. The L-3 PC and L-5 PC dialyzers induced more leukopenia and C3a generation than PAN but less than Cuprophan. Thus these new dialyzers offer conventional mass transfer and ultrafiltration rates with much improved membrane biocompatibility.

Aged↗
PubMed1986

Biocompatibility aspects of cellophane, cellulose acetate, polyacrylonitrile, polysulfone and polycarbonate hemodialyzers.

The biocompatibility of cuprammonium rayon (Cu), cellulose acetate, polysulfone (Ps) and polyacrylonitrile hollow-fiber dialyzers and a polycarbonate-polyether flat plate dialyzer has been investigated. The Cu dialyzer resulted in more complement activation and a greater degree of leukopenia than the others, while the Ps hollow-fiber dialyzer appeared to be the most biocompatible of the membrane equipment in this study. These results were confirmed by in vitro evaluations and microscopic examinations of the different dialyzers.

Acrylic Resins↗
PubMed1986

Biocompatibility of a new polycarbonate dialysis membrane.

The present report summarizes our experience with a new polycarbonate (PC)-based dialysis membrane (Gambro Lundia PRO-5) compared with a cuprophan (CP)-based membrane (Gambro Lundia 10-5N). Platelet count decreased during dialysis with CP, but was unchanged with PC membranes. Platelet injury, reflected by decreased platelet aggregation and increase in plasma beta-thromboglobulin, occurred equally with both membranes. Complement activation (C3d and C5a), leukopenia and release of granulocyte-derived elastase was more extensive with CP than with PC membranes. The new membrane represents an improvement of biocompatibility with respect to the complement-leukocyte system, whereas the effect on platelets resembles the injury caused by CP membranes.

Adenosine Diphosphate↗
PubMed1986

Evaluation and tolerance of a new polycarbonate membrane in elderly patients. Preliminary results.

We studied the performance and tolerance of a new capillary hemodialyzer using a polycarbonate membrane (Gambrane PCD 1000) in a group of 5 elderly patients (mean age 68 years). The ultrafiltration coefficient is 6 (justifying the monitoring control of weight loss) and clearances for small molecules are comparable with cellulosic membranes. A good tolerance during 300 sessions was observed; nevertheless, an important neutropenia was noted in 2 out of 5 patients. The complement activation measured by the dosage of the C3a Desarg fraction existed in all the patients, reaching an average 6 times the initial level compared to 40 times for Cuprophan. Complement activation and neutropenia are considerably reduced by the reuse of the hemodialyzer as it was described for the cellulosic membranes.

Age Factors↗
PubMed1986

Different in vitro generation of C3d by cuprammonium and polycarbonate capillary hemodialyzers.

Cellulosic membranes have been shown to activate C3 via the alternative pathway. Generation of the stable product C3d was compared in polycarbonate (PC) and cuprammonium (CU) hollow-fiber minidialyzers with identical geometry, using an in vitro recirculation system with platelet-poor plasma (recirculation rate 20 ml/min; 1,600 fibers; 0.115 m2; 40 ml system priming volume; recirculation time 120 min). After extensive washing, residual protein was removed by reverse transmembrane pressure (1.5 bar) from the air-filled dialysate compartment. Such protein fraction, functionally defined as 'secondary membrane', was similar in quantity for PC and CU fibers. Plasma proteins were present in the membrane without selective adsorption (flat-bed polyacrylamide gel electrophoresis and rocket immunoelectrophoresis using monospecific antibodies). C3d, measured by immunoelectrophoresis, increased with time in the fluid phase compartment of both dialysers, but C3d generation was consistently and significantly (p less than 0.05) less in PC than in CU dialysers. The observation documents an activation of C3 with PC, in contrast to previous reports of no activation. However, C3 activation with PC was less intense than with CU.

Adsorption↗
PubMed1978

Studies on red cell flexibility in spherocytosis using a polycarbonate membrane filtration method.

A method for studying red cell flexibility as reflected by red cell rigidity and fragility is described. Using an infusion pump, suspended red cells are filtered through a polycarbonate membrane with 3 micron pores. The filtration pressure, which is continuously monitored, is considered to reflect red cell rigidity. The hemoglobin released by the disruption of red cells passing through the membrane is regarded as an indirect measure of red cell fragility. In all of the patients with hereditary spherocytosis studied and in some of their symptomless relatives, the decreased flexibility observed was associable with increased rigidity of the red cell. In vitro effects of chlorpromazine and vinca alkaloid on red cell flexibility were also studied. High concentrations of chlorpromazine and vinblastine induced formation of spherocytes displaying altered cell flexibility.

Adult↗
PubMed2003

Surface modification of a polycarbonate-urethane using a vitamin-E-derivatized fluoroalkyl surface modifier.

Fluorinated surface-modifying macromolecules (SMMs) have been previously reported on and shown to limit the hydrolytic degradation of polyurethanes. The SMM molecules achieve this effect by allowing for the selective migration of terminal fluorinated groups to the polymer's surface, which may then shield more hydrolytically-sensitive groups in the base polyurethane backbone. A further extension of the SMM concept would be to utilize the migration of the fluorine tails to simultaneously deliver biologically active moieties to the surface. This study explored the synthesis and characterization of a vitamin-E (natural anti-oxidant) coupled surface modifier, as a model for the bioactive SMM concept. The SMM was synthesized using lysine diisocyanate (LDI), polycarbonate diol (PCN), and a fluoroalcohol. By derivatizing the LDI pendant ester, vitamin E was coupled to the SMM. The vitamin-E SMM was physically characterized using gel-permeation chromatography (GPC) and its anti-oxidant activity was assessed in the presence of 0.1 mM NaOCl. Polymer degradation experiments were carried out using 10 mM NaOCl incubation solutions, and the relative material breakdown was assessed using GPC and scanning electron microscopy (SEM). The results indicate that while the fluoro-component reduced damage of the PU, the bioactive component achieved a further deactivating effect. A similar action may also be effective against superoxide anions generated by human macrophages.

Biocompatible Materials↗
PubMed2005

Polycarbonate-urethane hard segment type influences esterase substrate specificity for human-macrophage-mediated biodegradation.

Previous studies have shown that esterase activity can degrade a variety of polyurethanes (PUs), including polycarbonate-based PUs (PCNUs). When cultured on PCNUs, differing in their chemistries, monocyte-derived macrophages (MDM) synthesized and secreted different amounts of both cholesterol esterase (CE) and monocyte-specific esterase (MSE). MDM were seeded on PCNUs synthesized with hexane diisocyanate (HDI) or 4,4'-methylene-bis-phenyl diisocyanate (MDI), PCN and [14C]butanediol (BD) in the ratio 3:2:1 (referred to as HDI321 or MDI321). The effect of phenylmethylsulfonyl fluoride (PMSF, a serine esterase and proteinase inhibitor), sodium fluoride (NaF, a MSE inhibitor) and sodium taurocholate (NaT, a CE stimulator) was assessed on degradation (measured by radiolabel release (RR)) and esterase activity in MDM lysate. The results were compared to the effect that these reagents had on commercially available CE and carboxyl esterase (CXE), which has a specificity similar to MSE. NaF inhibited CXE- and MDM-mediated RR to the same extent as for both PCNUs. However, the MDM-mediated RR from MDI321 was 1.8-times higher than HDI321 in the presence of NaT (P = 0.005). This study suggests that the difference in diisocyanate chemistry may dictate the relative contribution of each esterase to a specific material's degradation. This may be related to both the substrate specificity of each esterase, as well as by the relative amount of each esterase that the specific biomaterial substrates induce the cells to synthesize and secrete.

Biocompatible Materials↗
PubMed2006

Electrospun mat of tyrosine-derived polycarbonate fibers for potential use as tissue scaffolding material.

Desaminotyrosyl-tyrosine ethyl ester (DTE) and desaminotyrosyl-tyrosine (DT) were used as monomers in the synthesis of two tyrosine-derived polycarbonates: the slow degrading homopolymer poly(DTE carbonate) and the fast degrading co-polymer poly(DTE-co-20%DT carbonate). Ultrafine fibers of these polymers were successfully fabricated using an electrospinning process. The effects of some solution and process parameters (i.e., polymer concentration, electrostatic field strength and solvent system) on morphological appearance and diameters of the obtained fibers were investigated by scanning electron microscopy (SEM). Smooth fibers were obtained at high enough solution concentrations (i.e., 15 and 20% (w/v)). The average fiber diameter was found to increase with increasing polymer concentration and applied electrostatic field strength. The electrospinnability of poly(DTE-co-20%DT carbonate) in dichloromethane was enhanced when methanol was used as the co-solvent. In all of the conditions investigated, the average diameter of the obtained smooth fibers ranged between 1.9 and 5.8 microm. A qualitative assessment of an as-spun mat of poly(DTE carbonate) fibers as a tissue scaffolding material showed that three different cultured cell lines appeared to adhere and propagate well within the scaffold. For poly(DTE carbonate) exceptionally high cell densities could be achieved after 10 days of cell culture.

Animals↗