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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim was to study the effect of the type of polymer solvent on characteristics of microspheres produced by spray drying. The water-soluble model protein, bovine serum albumin (BSA) was microencapsulated into biodegradable poly(D,L-lactic acid) using the following 10 different polymer solvents: acetaldehyde dimethyl acetal, acetone, dichloromethane, dioxane, ethyl acetate, ethyl vinyl ether, nitromethane, tetrahydrofuran, 1,1,1-trichloroethane, and 1,1,2-trichloroethylene. These solvents having similar toxicity levels differ greatly in their physico-chemical characteristics such as boiling point, vapour pressure, miscibility and interfacial tension with an aqueous phase, and solubility parameter. The effect of these solvents on microsphere morphology was studied by SEM-micrographs. Regular particle morphology was obtained when dichloromethane, ethyl acetate, or nitromethane was used as the polymer solvent, whereas the trichlorinated solvents, tetrahydrofuran, and dioxane produced a substantial number of coalesced particles. The results are interpreted in terms of boiling point, vapour pressure, and polymer-solvent affinity. Further, BSA-loading and -integrity in the microspheres, and burst release were analysed. The theoretical loading of 2.9% was attained with dichloromethane, ethyl acetate and nitromethane, in agreement with observations of particle morphology. HPLC- and SDS-PAGE analysis of the microencapsulated BSA did not show any protein degradation or dimerization, whereas solid-phase ELISA clearly revealed that the in vitro protein antigenicity was substantially reduced (50%), particularly by water miscible solvents. Dichloromethane and ethyl acetate did not show any detrimental effect on protein antigenicity. Finally, burst release could be related again to particle morphology, with dichloromethane and nitromethane giving a burst release of only 5%. In conclusion, dichloromethane, ethyl acetate and nitromethane proved to be the most suitable solvents for the polymer-protein system studied.
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PMID:Quality improvement of spray-dried, protein-loaded D,L-PLA microspheres by appropriate polymer solvent selection. 773 Sep 60

Adhesion characteristics of fibroblastic baby hamster kidney (BHK) cells and epithelial Madine Darby kidney (MDBK) cells on polyurethane (PU) and polyhydroxyethylmethacrylate (PHEMA) based surfaces have been studied. PU surfaces were prepared by a classical solvent-casting procedure of Pellethane solution that contains different types of solvents, i.e., THF, dioxane and their compositions. PHEMA based surfaces were obtained by bulk polymerization of respective comonomers (HEMA, acrylic acid, AA, and dimethylaminoethylmethacrylate, DMAEMA) in the presence of the crosslinker. Thus, a number of polymeric surfaces were obtained with different surface charges (COO- and NH+4) and with different surface free energies in a range between 60-82 ergs/cm2. Surface properties of these membranes were characterized by equilibrium water contents, air and octane contact angles, surface free energies, SEM photographs and ATR-FTIR spectra. Interactions of BHK and MDBK cells with the surfaces were examined in stationary culture conditions which were carried out in MEM supplemented with fetal calf serum. The observations strongly suggested that the chemical and/or physical properties of membrane surface and morphology of the cell control the degree of cell adhesion to the PU and PHEMA based membranes.
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PMID:Relationship of surface characteristics to cellular attachment in PU and PHEMA. 845 35

Alkylation of 3,17 beta-bis(2-trimethylsilyl)ethoxymethyl-1,3,5(10) estratriene-6-one (2) with 5-bromo-1-pentene using NaHMDS in THF afforded 3,17 beta-bis(2-trimethylsilyl)ethoxymethyl-7-alpha-(4'pentenyl)-1,3,5(10) estratriene-6-one (3) in excellent stereoselectivity (> 95% epimeric excess). Functionalization of the side chain in compound 3 was accomplished via ozonolysis, oxidation and esterification to give 5 in 72% yield. The reduction of ester (5) using NaBH4 in MeOH afforded the corresponding 6 alpha-hydroxy compound (6) as a single isomer in 72% yield. The hydroxyl group in 6 was removed by converting to the corresponding xanthate (7) followed by reduction using n-Bu3SnH to afford 8 in good yield. Finally, the SEM protective groups in 8 were removed, after which the ester function was hydrolyzed with LiOH to give 7 alpha-(3'-carboxypropyl)estradiol (10), in 10.6% overall yield from 3.
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PMID:A stereoselective synthesis of 7 alpha-(3-carboxypropyl) estradiol from a noncontrolled substance. 943 42

In order to select a candidate segmented polyurethane (SPU) elastomer for cardiovascular prostheses, a series of physical tests was carried out on five commercially available biomedical polyurethanes. The tests were performed on uniformly thick sheets (0.2-0.3 mm), obtained by solvent casting from THF (Cardiothane 51, Pellethane 2363 80A, Estane 5714 F1, and Estane 58810) or DMAC (Biomer). Tensile mechanical tests at 23 and 37 degrees C showed for all the copolymers typical stress/strain behaviour of elastomeric materials, with small individual differences. Hydrolytic stability was investigated at 85, 60, and 37 degrees C, at increasing times of exposure (96-168 h), in water or alkaline buffer (pH = 10). As indicated by gel permeation chromatography, in almost all cases a degradation of the molecular weight (particularly the M w) was noticed after the hydrolytic tests, but tensile, thermal (by DSC) and dynamic mechanical properties were substantially not affected. SEM was also performed on the materials, before and after the hydrolytic tests. Changes in the morphology of the materials (related to degradation effects) was observed only in the case of Biomer, as shown also by the thermomechanical analyses. After this first series of physical tests, a clear choice of a particular SPU among the five investigated was not found.
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PMID:Comparative physical tests on segmented polyurethanes for cardiovascular applications. 1014 49

Polyurethane/liquid crystal composite membranes were first suggested to be used as biomaterials. In our work, three series of polyurethane/liquid crystal composite membranes based on three different kinds of liquid crystal compounds [N-(-4-methyoxybenzylidene)-4'-heptylaniline, 4-pentyl-4'-nitrile-biphenyl and cholesteryl oleyl carbonate] were prepared by casting on glass plates from a tetrahydrofuran (THF) solution of polymer and liquid crystal at room temperature. In our opinion, the formation of liquid crystal phase on the composite membrane surface is the basic requirement for getting better biomaterial. The result of this work is in accordance with our opinion. The effect of liquid crystal content on the formation of liquid crystal phase was identified by the observation of optical polarization microscopy (OPM). The results showed that the content of liquid crystal in composite membrane must be more than 30% (wt) in order to form liquid crystal phase on the composite membrane surface. The blood-compatibility of the composite membranes was assessed from SEM observation of the platelet's adhesion to membrane's surface, blood clotting time and haemolysis ratio. The observation of platelet's adhesion showed that the platelets gathered together on the pure polyurethane films, but the amount of platelets which were adherent on the surface covered by the liquid crystal phase was fewer than that of pure polyurethane film when platelet-rich plasma was allowed to be in contact with the membranes for 1 h at room temperature. The determination of blood clotting time and haemolysis ratio showed that these polyurethane/liquid crystal composite membranes, in which the content of liquid crystal was more than 30% (wt), appear to be beneficial in improving the blood compatibility and reducing the thrombogenicity.
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PMID:Blood-compatibility of polyurethane/liquid crystal composite membranes. 1055 76

Polysiloxane/liquid crystal composite membrane was first suggested to be used as biomaterials. In this work, the polydimethyl-methylhydrosiloxane and polydimethyl-methylethylenesilosiane, as a substrate, were blended with cholesteryl oleyl carbonate (COC) in tetrahydrofuran, and then crosslinked into membranes on glass plates by means of the platinum catalyst at 110 degrees C for 20 min. The effects of the liquid-crystal content in composite membranes on the formation of liquid-crystal phase were verified by the observation of optical polarization microscopy. The relationship between the morphology of the composite membranes and blood compatibility was identified by the dynamic blood-clotting tests, haemolysis ratio measurement, platelet adhesion and SEM observation. The results show that the blood-compatibility of composite membranes with the concentration of liquid crystal 20, 30% (wt) is more excellent than that of other composite membranes.
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PMID:Preparation and blood compatibility of polysiloxane/liquid-crystal composite membranes. 1151 78

A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1 x 10(-7) mg mL(-1 )up to 1 x 10(-3) mg mL(-1) [correlation coefficient ( r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL(-1)). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement.
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PMID:Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer. 1474 73

Nanostructured metal films of platinum, gold and silver up to 675 nm thick we prepared by electrochemical deposition through templates of 700 nm diameter polystyrene spheres assembled as hexagonal close packed monolayer on an evaporated gold surface followed by removal of the template by dissolution in tetrahydrofuran. The reflection spectra of the films at normal incidence were recorded as a function of film thickness and the spectra correlated with the local visual appearance of the film and the surface structure from SEM. For thin films, below one quarter sphere height, the spectra show a single reflectivity dip at a wavelength just below the sphere diameter consistent with surface-plasmon grating-like behaviour. For the thicker films several reflectivity dips are observed which move towards longer wavelength with increasing film thickness. This behaviour is shown to be consistent with a model in which light reflected from the top of the structure interferes with light reflected from within the spherical segment cavities in the film.
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PMID:Optical properties of nanostructured metal films. 1475 Jun 67

This work describes the synthesis of new amphiphilic perfluorohexyl- and perfluorooctyl-propanethio-beta-cyclodextrins and the comparison of the ability of these molecules and alkyl analogue, nonanethio-beta-cyclodextrin to form nanospheres. Nanospheres were prepared using nanoprecipitation method (perfluoroalkylthio-beta-cyclodextrin in THF [0.11 x 10(-3)M], stirring rate 700rpm, addition of aqueous phase at 64 degrees C into organic phase at 50 degrees C). They were characterised by Photon Correlation Spectroscopy (PCS) and by electron microscopy (SEM and cryo-TEM). The nanospheres prepared from these new beta-cyclodextrin derivatives have an average size of 260nm, and appear to be spherical in cryo-TEM images. Whereas alkyl analogue forms polydisperse aggregates with sizes in the range 60-350nm.
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PMID:Synthesis and characterisation of novel nanospheres made from amphiphilic perfluoroalkylthio-beta-cyclodextrins. 1584 64

Polysaccharide multilayer nanocapsules have been fabricated in aqueous media by the layer-by-layer self-assembly of chitosan (CHI) and sodium alginate (ALG) on monodisperse polystyrene (PS) nanoparticles with a diameter of 180 nm as template, followed by removal of the templates through dissolving in THF. The pH and added salt concentration of the polyelectrolyte deposition solutions were optimized to ensure the alternating deposition. Consequently, the most suitable pH values were found to be 6.0-8.0 for ALG and 3.5 for CHI and were used in the deposition. The concentration of added NaCl used in the adsorption solutions was 0.5 M, which led to an average thickness of about 13 nm for 5 bilayers of CHI/ALG shell-wall. zeta-potential indicated the stepwise and alternating adsorption of CHI and ALG to form multilayer film on the PS nanoparticles. The characteristic bands of PS residue almost disappeared in the IR spectrum of the nanocapsule after dipped in THF, confirming thorough removal of PS templates from the core-shell particles. TEM, SEM and AFM were utilized to observe the nanocapsules of about 225 nm in diameter (by TEM). A hydrophilic drug model, acridine hydrochloride (AH), was chosen to investigate the loading and release properties of the nanocapsules. The positively charged AH spontaneously deposited into the capsule due to the electrostatic interaction with the negatively charged styrene sulfonate residues from the PS template inside the capsule. The rate of AH release became slightly slower when the capsule wall was cross-linked with glutaraldehyde, but the accumulative released amount for the cross-linked capsule was obviously reduced. These nanocapsules made from nature polysaccharides have a potential application in controlled drug release.
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PMID:Multilayer nanocapsules of polysaccharide chitosan and alginate through layer-by-layer assembly directly on PS nanoparticles for release. 1612 96


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