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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study, the process included aqueous Poly (vinyl alcohol) solutions frozen at -20 degrees C for 6-12 h, and then thawed for 1-2 h. The same process was repeated 1-3 times. After the specimen was dehydrated in vacuum, a kind of artificial articular cartilage--PVA-hydrogel was made up. Subsequently, the micromorphology of PVA-hydrogel was observed by means of optical microscopy and SEM. DSC and mechanical tests were employed in ivestigating the influence of freesing, thawing, dehydrating and irradiating upon the crystallity and the mechanical properties of PVA-hydrogel.
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PMID:[The development of a kind of artificial articular cartilage-PVA-hydrogel]. 1255 67

Alginate-(Poly-L-Lysine)-Alginate(APA) microcapsules were prepared by Electrostatic Droplet Generator(EDG) technique and the thickness of microcapsule membrane, which was composed by polyelectrolyte complex, were studied in this paper. The theoretical formula was given for the measurement of membrane thickness of APA microcapsules by element analysis of membrane and calculation. The membrane thickness was 7-10 microns by theoretical calculation. On the other hand, the thickness of membrane was measured by SEM and optical microscopy and the results were 7 microns and 12 microns, respectively. The results showed that theoretical calculation is in good accordance with experimental determoination of mermbrane thickness and the membrane thickness of APA microcapsule is about 7-10 microns. The optical microscopy is an easy way to measure membrane thickness.
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PMID:[Theoretical calculation and experimental study of membrane thickness of alginate-(poly-L-lysine)-alginate microcapsules]. 1256 69

We report the development of new biomacromolecule coatings on biodegradable biomaterials based on electrostatic assembly of extracellular matrix-like molecules. Poly(ethylene imine) (PEI) was employed to engineer poly(dl-lactide) (PDL-LA) substrate to obtain a stable positively charged surface. An extracellular matrix- (ECM-) like biomacromolecule, gelatin, was selected as the polyelectrolyte to deposit on the activated PDL-LA substrate via the electrostatic assemble technique. The extracellular matrix-like multilayer on the PDL-LA substrate was investigated by attenuated total reflection (ATR-FTIR), X-ray photoelectron spectrscopy (XPS), contact angle, and atomic force microscopy (AFM). The gradual buildup of the protein layer was investigated by UV-vis spectra, and it was further given a quantitative analysis of the protein layer on the PDL-LA substrate via the radioiodination technique. The stability of the protein layer under aqueous condition was also tested by the radiolabeling method. Chondrocyte was selected as the model system for testing the cell behavior and morphology on modified PDL-LA substrates. The chondrocyte test about cell attachment, proliferation, cell activity and cell morphology by SEM, and confocal laser scanning microscopy (CLSM) investigation on extracellular matrix-like multilayer modified PDL-LA substrate was shown to promote chondrocyte attachment and growth. Comparing conventional coating methods, polyelectrolyte multiplayers are easy and stable to prepare. It may be a good choice for the modification of 3-D scaffolds used in tissue engineering. These very flexible systems allow broad medical applications for drug delivery and tissue engineering.
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PMID:Surface engineering of poly(DL-lactide) via electrostatic self-assembly of extracellular matrix-like molecules. 1262 35

Anti-low density lipoprotein antibody (anti-LDL antibody) attached poly(2-hydroxyethyl methacrylate-methacryloylamidophenylalanine) (poly(HEMA-MAPA)) beads were prepared for selective removal of cholesterol from hypercholesterolemic human plasma. Poly(HEMA-MAPA) beads were produced by a modified suspension polymerization and then characterized by swelling tests and SEM. Blood-compatibility tests were also investigated. The water swelling ratio of the poly(HEMA-MAPA) beads increased significantly (68%) compared with pHEMA (55%). All the clotting times increased when compared with poly(HEMA) beads. Loss of platelets and leukocytes was very low. The maximum anti-LDL antibody attachment was achieved at pH 7.0. Attachment of anti-LDL antibody was 29.6 mg/g. There was a very low non-specific cholesterol binding onto the poly(HEMA-MAPA) beads, about 0.74 mg/g. Anti-LDL antibody attached beads adsorbed in the range of 13.3-16.0 mg cholesterol/g from hypercholesterolemic human plasma. Up to 92% of the adsorbed LDL was desorbed. The binding-elution cycle was repeated 10 times using the same beads. There was no significant loss of binding capacity.
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PMID:Immunoaffinity beads for selective removal of cholesterol from human plasma. 1280 43

Metal-chelating ligand and/or comonomer 2-methacrylolyamidohistidine (MAH) was synthesized by using methacryloyl chloride and L-histidine methyl ester. MAH was characterized by NMR and FTIR. Spherical beads with an average diameter of 75-125 microm were produced by suspension polymerization of methylmethacrylate (MMA) and MAH carried out in an aqueous dispersion medium. Poly(MMA-MAH) beads had a specific surface area of 37.5 m(2)/g. Poly(MMA-MAH) beads were characterized by water uptake studies, FTIR, SEM and elemental analysis. Elemental analysis of MAH for nitrogen was estimated as 34.7 microM/g of polymer. Then, Cu(2+) ions were chelated on the beads. Cu(2+)-chelated beads with a swelling ratio of 38% were used in the adsorption of human-immunoglobulin G (HIgG) from both aqueous solutions and human plasma. The maximum adsorption capacities of the Cu(2+)-chelated beads were found to be 12.2 mg/g at pH 6.5 in phosphate buffer and 15.7 mg/g at pH 7.0 in MOPS. Higher adsorption value was obtained from human plasma (up to 54.3 mg/g) with a purity of 90.7%. The metal-chelate affinity beads allowed one-step separation of HIgG from human plasma. The adsorption-desorption cycle was repeated 10 times using the same beads without noticeable loss in their HIgG adsorption capacity.
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PMID:Novel metal-chelate affinity adsorbent for purification of immunoglobulin-G from human plasma. 1295 73

Poly(DL-lactide) (PDLLA) foams and bioactive glass (Bioglass) particles were used to form bioresorbable and bioactive composite scaffolds for applications in bone tissue engineering. A thermally induced phase separation process was applied to prepare highly porous PDLLA foams filled with 10 wt % Bioglass particles. Stable and homogeneous layers of Bioglass particles on the surface of the PDLLA/Bioglass composite foams as well as infiltration of Bioglass particles throughout the porous network were achieved using a slurry-dipping technique. The quality of the bioactive glass coatings was reproducible in terms of thickness and microstructure. In vitro studies in simulated body fluid (SBF) were performed to study the formation of hydroxyapatite (HA) on the surface of the PDLLA/Bioglass composites, as an indication of the bioactivity of the materials. Formation of the HA layer after immersion in SBF was confirmed by X-ray diffraction and Raman spectroscopy measurements. The rate of HA formation in Bioglass-coated samples was higher than that observed in non-coated samples. SEM analysis showed that the HA layer thickness rapidly increased with increasing time in SBF in the Bioglass-coated samples. The high bioactivity of the developed composites suggests that the materials are attractive for use as bioactive, resorbable scaffolds in bone tissue engineering.
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PMID:Bioresorbable and bioactive composite materials based on polylactide foams filled with and coated by Bioglass particles for tissue engineering applications. 1534 48

Chemically crosslinked biodegradable hydrogels based on di-acrylated Pluronic F-127 tri-block copolymer were prepared by a photopolymerization method. Poly(lactic acid-co-glycolic acid) (PLGA) microspheres were physically entrapped within the Pluronic hydrogel in order to modulate the local pH environment by acidic degradation by-products of PLGA microspheres. The PLGA microspheres were slowly degraded to create an acidic microenvironment, which facilitated the cleavage of an acid-labile ester-linkage in the biodegradable Pluronic hydrogel network. The presence of PLGA microspheres accelerated the degradation of the Pluronic hydrogel and enhanced the protein release rate when protein was loaded in the hydrogel.SEM image of photo-crosslinked Pluronic hydrogel entrapping PLGA microspheres.
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PMID:Controlling degradation of acid-hydrolyzable pluronic hydrogels by physical entrapment of poly(lactic acid-co-glycolic acid) microspheres. 1548 26

Poly(2-hydroxyethyl methacrylate) hydrogels were prepared in the presence of varying concentrations of water, or a co-monomer ethoxyethyl methacrylate at different strengths of crosslinking agent ethylene glycol dimethacrylate. Calcification tendency and its correlation with monomer mixture composition, topography and porosity of these materials were investigated. Scanning (SEM) and transmission electron microscopy (TEM) was used to study topography and porosity respectively. Calcification and calcium diffusion ability in to the hydrogels were investigated by light microscopy, SEM and energy dispersive analysis of X-rays (EDAX) after incubation of the materials in a metastable calcifying solution for 48 days. Polymer and solvent volume fractions were also studied to determine if a correlation existed between porosity and calcification. Most of the series of hydrogels showed surface irregularities. Internal structure showed evidence of a porous structure in one of the series. Calcification studies indicated diffusion of calcium ions in some of the series. The diffusion of calcium is limited to 30-40 microm in most calcified specimens. For hydrogels that exhibited substantial surface irregularities and micro channels, the infiltration of calcium up to 200 microm was observed. Attempts to detect porosity by electron microscopy failed in some of the hydrogels due to difficulty in sample processing and sectioning. However, collaboration of the results with different techniques used, indicated that surface defects are the major contributors to calcium deposition. Decrease in porosity reduces the amount of calcium deposits and infiltration with decreasing solvent volume fraction which is associated with crosslinking concentration and initial water content of the polymer.
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PMID:Morphological and topographic effects on calcification tendency of pHEMA hydrogels. 1594 46

Poly-L-Lysine (PLL) is the most widely used biomaterial for providing perm-selectivity in alginate microcapsules for islet transplantation. We had previously reported that Poly-L-Ornithine (PLO) is less immunogenic than PLL, and in the present study, we have compared the physical characteristics of PLO- and PLL-coated hollow alginate microcapsules. Microspheres made with 1.5% alginate were divided into 2 groups that were first coated with either 0.1% PLO or PLL, followed by a second coating with 0.25% alginate. After liquefaction of the inner alginate core with sodium citrate, the microcapsules were washed with saline and used for experiments. Pore size exclusion studies were performed with FITC-labeled lectins incubated with encapsulated pig islets followed by examination for fluorescence activity. Mechanical strength was assessed by an osmotic pressure test and by 36 h of mechanical agitation of microcapsules with inert soda lime beads. The pore size exclusion limit of microcapsules after 20 min of coating was significantly smaller with PLO. While the mean +/- SEM diameter of PLL-coated microcapsules increased from 718+/-17 to 821 +/- 17 microm (p < 0.05) during 14 days incubation at 37 degrees C, the PLO group did not change in size. Also, PLL group had a higher percentage of broken capsules (52.7 +/- 4.9%) compared to 3.1 +/- 2.05% for PLO capsules (p < 0.0001,n = 6). We conclude that PLO-coated alginate microcapsules are mechanically stronger and provide better perm-selectivity than PLL-coated microcapsules.
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PMID:Characteristics of Poly-L-Ornithine-coated alginate microcapsules. 1595 58

Poly(1-methylimidazoliummethyl styrene)-surface grafted-poly(styrene) resin was prepared for the first time as a polymer-supported N-heterocyclic carbene (NHC) precursor for palladium complex by suspension polymerization. To prepare this polymer-supported NHC precursor, 1-methyl-3-(4-vinylbenzyl)imidazolium hexafluorophosphate, [MVBIM][PF6-], was synthesized as a monomer and copolymerized with styrene and DVB in water. This polymer-supported NHC precursor with imidazolium as a ligand, which exists solely on the surface of the resin, was well characterized by FE-SEM, CLSM, and IR spectroscopy. The precursor containing imidazolium readily formed a stable complex with Pd(OAc)2, and this polymer-supported N-heterocyclic carbene-palladium complex exhibited excellent catalytic activity for Suzuki cross-coupling reaction in an aqueous medium. The catalyst was recovered quantitatively from the reaction mixture by simple filtration and was able to be reused for a number of recycles with consistent activity in all of the coupling reactions.
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PMID:Polymer-supported N-heterocyclic carbene-palladium complex for heterogeneous Suzuki cross-coupling reaction. 1609 91


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