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

Microspheres of a polyelectrolyte complex hydrogel were prepared from chitosan and xanthan after interaction between the two polyionic polymers. Their biodegradation was studied vs. chitosan. Simulated gastric fluid (SGF, pH 1.2) and intestinal fluid (SIF, pH 7.5) both as biodegradation media and phosphate buffered saline (PBS, pH 7.4) as a negative control were used. The degradation studies were performed at 37 degrees C at 240 rpm permanent stirring to mimic the physiologic conditions. High performance liquid chromatography (HPLC) was carried out to quantify the chitosan degradation products using glucosamine (GA) and N-acetyl-D-glucosamine (N-Ac-GA) as references. The peaks area integration method was used to determine the amount of each degradation product as a function of incubation time in the media. The effect of the media on the morphological structure of microspheres was assessed by scanning electron microscopy. From HPLC studies, it appeared that in SGF and SIF the major degradation products were glucosamine (GA) and N-acetyl-D-glucosamine (NAc-GA). In the first 15 days, oligochitosan fractions were released from the complex, whereas N-acetyl-D-glucosamine was detected in the media after this period. The degradation kinetics were assessed by the measurement of the cumulative degradation products, which showed faster degradation of chitosan than the complex in SGF and SIF. SEM micrographs showed an enhancement of microsphere porosity as a function of incubation time in the simulated physiological media. Our results suggest a better control of the degradation kinetics when chitosan is complexed to xanthan.
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PMID:Study of biodegradation behavior of chitosan-xanthan microspheres in simulated physiological media. 1098 9

The study reports on secretion production and composition in the tubular glands of the canine anal sacs. For this purpose, light and electron microscopical (TEM, SEM) as well as several histochemical methods for the demonstration of lysosomal acidity, lipofuscin, and complex carbohydrates were used. The glandular tubules exhibited a pseudostratified epithelium with secretory cells of a different shape as related to secretion production activity, and regionally varying amounts of basal cells. Flat, cuboidal or columnar cells with or without apocrine-like protrusions were assembled in one glandular endpiece, although grouping of these cell types often occurred. Active secretory cells were columnar with many cytoplasmic vesicles and a typically merocrine and/or micro-apocrine exocytosis of vesicle contents. Additionally, many lysosomes of different sizes could be found, whereby in aged cells giant secondary lysosomes (autophagolysosomes, about 7 microm in diameter) occupied the major cell part. These giant lysosomes were shed by an apocrine-like process forming a final bottleneck stage of the upper cell part, and consisted of ceroid-type lipofuscin. The general carbohydrate histochemical and the lectin histochemical methods revealed that the secretion produced was composed of strongly concentrated neutral glycoproteins with the following saccharide residues: alpha-D-mannose, beta-D-galactose, beta-N-acetyl-D-glucosamine, alpha-L-fucose and N-acetyl-neuraminic acid (sialic acid); the luminal secretion contained only beta-D-galactose and, especially, N-acetyl-neuraminic acid. This luminal secretion showed a spatially orientated maturation beginning in terminal tubular regions and finishing near the excretory duct, independent of the different secretory cell types. The results obtained demonstrated highly active secretion production, with a regional variation in the glandular tubule, and at least three different modes of secretion by the secretory cells, whereby the shedding of giant lipofuscin granules seems to be very specific. The high amounts of sialic acids in the glycoproteins found may influence the rheological properties of the secretion by their water-binding capacities.
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PMID:Cytological and lectin histochemical characterization of secretion production and secretion composition in the tubular glands of the canine anal sacs. 1117 5

Calcium phosphate growth on chitin phosphorylated fibres was studied using scanning electron microscopy and energy dispersive X-ray analysis (SEM, EDX), micro-Fourier transform infrared spectroscopy (FTIR), and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. The C6 chemical shift positions of 13C MAS NMR in the chitin fibres phosphorylated using urea and H3PO4 are obvious indicating that phosphorylation takes place not in the C1 but in the C6 region. Micro-FTIR and 31P MAS NMR suggested that ammonium hydrogen phosphate formed during the phosphorylation procedure. Chitin fibres phosphorylated using urea and H3PO4 and then soaked in saturated Ca(OH)2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of the PO4 functionalities, were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5xSBF solution for as little as one day. The thin layer after Ca(OH)2 treatment functioned as a nucleation layer for further calcium phosphate deposition after soaking in 1.5xSBF solution. EDX-measured Ca : P ratios of the coatings of Ca(OH)2-treated phosphorylated chitin in 1.5xSBF solution suggested that calcium-deficient apatite was formed.
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PMID:Growth of calcium phosphate on phosphorylated chitin fibres. 1534 22

Anaerobic fungi were isolated from both the rumen and faeces of nine sheep and a cow. A reliable and simple method for the isolation of anaerobic fungi using 24 h rumen incubated milled straw as the inoculum source was developed. We also evaluate the use of chitin measurements as an assay of rumen fungal biomass. Chitin levels were determined from various sample sources (milled barley straw used as the fungal culture substrate in vitro; plant particulate digests from the rumen (PLP) and centrifuged strained rumen fluid (CSRF) using both HPLC and colorimetric methods. Both methods were highly correlated and consequently the simpler colorimetric method was adopted for subsequent studies. There was also a high degree of correlation between anaerobic fungal cellulase activities with the assayed chitin content of milled barley straw cultures over 12 d of an in vitro experiment. The colorimetric chitin assay protocol was then used to assess the diurnal variation and abundance of rumen fungi in in vivo assays. We assessed the distribution of chitin (mg g(-1) dry matter) in various fractions of the strained rumen fluid (SRF) and PLP samples from the rumen of sheep. Chitin was detected in all fractions of strained rumen fluid but the main source of chitin in the samples may be attributed to the fungal biomass. We did not detect any significant differences in chitin levels over a 24 h sampling period. Finally, an SEM study on subsamples of milled straw and plant particulate matter used in the chitin assays, revealed that the pattern of the fungal development on substrate material differs from the culture medium to the rumen.
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PMID:Methods for the isolation, culture and assessment of the status of anaerobic rumen chytrids in both in vitro and in vivo systems. 1553 72

Beauveria bassiana is a well-known broad-range arthropod pathogen which has been used in biological control of several pest insects and ticks such as Boophilus microplus. Beauveria amorpha has both endophytic and entomopathogenic characteristics, but its capacity for biological control has still not been studied. During the processes of host infection, B. bassiana and B. amorpha produce several hydrolytic extracellular enzymes, including proteases and chitinases, which probably degrade the host cuticle and are suggested to be pathogenicity determinants. To access the role of these enzymes during infection in the tick B. microplus, we analyzed their secretion during fungus growth in single and combined carbon sources, compared to complex substrates such as chitin and B. microplus cuticle. Chitin and tick cuticle-induced chitinase in both fungus and protease was induced only by tick cuticle. SEM analysis of B. amorpha and B. bassiana infecting B. microplus showed apressorium formation during penetration on cattle tick cuticle.
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PMID:Boophilus microplus infection by Beauveria amorpha and Beauveria bassiana: SEM analysis and regulation of subtilisin-like proteases and chitinases. 1588 12

In this study three model drugs (N-acetyl-D-glucosamine (NAG), anhydrous caffeine, and propranolol hydrochloride) were agglomerated with starch acetate (SA) by mixing the binary powders on a stainless steel (SS) plate. Agglomeration was induced by triboelectrification of the particles during mixing, and it was evaluated as a method to achieve controlled drug release rate. These agglomerates, mixed with different amounts of a disintegrant, were compressed into tablets whose dissolution characteristics were determined. Triboelectric measurements showed that when the drugs were in contact with SS, charges of the opposite polarity were generated to SA (+) and caffeine and NAG (-) promoting adhesion. Instead, propranolol HCl was charged with the same polarity as SA. SEM micrographs showed that smaller caffeine particles, in spite of their larger negative charge, agglomerated less efficiently with SA than larger NAG particles. This emphasizes the importance of particle size in the agglomeration process. Propranolol HCl did not form agglomerates with SA since their particle sizes and charges were identical. As a result, agglomeration of powders prior to tablet compression allows for modification and control of the release rate of the drugs from the SA matrix tablets as well as the tensile strength of the tablets.
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PMID:Modifying drug release and tablet properties of starch acetate tablets by dry powder agglomeration. 1707 68

Chitin nanofibers were prepared from dried crab shells by a simple grinding treatment in a never-dried state under an acidic condition after the removal of proteins and minerals. The obtained nanofibers were observed by FE-SEM and found to have a uniform width of approximately 10-20 nm and high aspect ratio; both these findings were similar to those for nanofibers from prawns. Furthermore, it was confirmed that the nanofibers were extracted from the natural chitin/protein/mineral composites of crab shell in their original state. That is, the N-acetyl group was not removed and the alpha-chitin crystal structure was maintained, as confirmed by elemental analysis data, FT-IR spectra, and X-ray diffraction profiles.
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PMID:Preparation of chitin nanofibers with a uniform width as alpha-chitin from crab shells. 1939 58

Chitin is a novel biopolymer and has excellent biological properties such as biodegradation in the human body and biocompatible, bioabsorable, antibacterial and wound healing activities. In this work, alpha- and beta-chitin membranes were prepared using alpha- and beta-chitin hydrogel. The bioactivity studies were carried out using these chitin membranes with the simulated body fluid solution (SBF) for 7, 14 and 21 days. After 7, 14 and 21 days the membranes were characterized using SEM, EDS and FT-IR. The SEM, EDS and FT-IR studies confirmed the formation of calcium phosphate layer on the surface of the both chitin membranes. These results indicate that the prepared chitin membranes were bioactive. Cell adhesion studies were also carried out using MG-63 osteoblast-like cells. The cells were adhered and spread over the membrane after 24h of incubation. These results indicated that the chitin membranes could be used for tissue-engineering applications.
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PMID:Bioactive and osteoblast cell attachment studies of novel alpha- and beta-chitin membranes for tissue-engineering applications. 1952 84

Chitin nanofibers were acetylated to modify the fiber surface and were characterized in detail. The acetyl DS could be controlled from 0.99 to 2.96 by changing the reaction time. FT-IR spectra indicate that chitin nanofibers were acetylated completely after 50 min reaction time. X-ray diffraction profiles and TGA curves show that the chitin nanofibers were acetylated heterogeneously from the surface to the core. SEM images show that fiber shape was maintained even in the high-DS sample and that the thickness of the nanofibers increased with the introduction of bulky acetyl groups. Acetylated chitin nanofiber composites were fabricated with acrylic resin with the fiber content of approximately 25 wt %. Due to the size effect, all nanocomposites had high transparency, despite the variety of acetyl DS, and the transparency of the chitin nanofiber composite was less sensitive to acetylation. By only 1 min acetylation, the moisture absorption of the nanocomposite drastically decreased from 4.0 to 2.2%. Although the coefficient of thermal expansion (CTE) of the tricyclodecane dimethanol dimethacrylate (TCDDMA) resin was 6.4 x 10(-5) degrees C(-1), the CTE of the chitin nanofiber/TCDDMA composite decreased to 2.3 x 10(-5) degrees C(-1) by the reinforcement effect of the chitin nanofibers with low thermal expansion.
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PMID:Acetylation of chitin nanofibers and their transparent nanocomposite films. 2035 73

Chitin (C), a biopolymer which showed moderate sorption capacity (SC) towards Cu(II) and Fe(III) was suitably modified to enhance the SC. Three types of modifications viz., protonated chitin (PC), carboxylated chitin (CC) and grafted chitin (GC) were carried out to increase the SC. The modified forms of chitin showed enhanced SC for both Cu(II) and Fe(III) than the raw chitin. These sorbents were characterized by the FTIR and SEM with EDAX analysis. The various influencing parameters viz., contact time, pH and the interference of common anions during the sorption have been investigated. The sorption data was reasonably explained using Freundlich and Langmuir isotherms. The calculated values of thermodynamic parameters indicated that, the sorption is spontaneous and endothermic in nature. The order of selectivity of Cu(II) and Fe(III) on modified chitin was found to be Fe(III)>Cu(II). The suitability of modified chitin has been tested with the field samples collected in a near by industrial area. The suitable mechanism for the respective metal removal has been established.
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PMID:Preparation and metal uptake studies of modified forms of chitin. 2070 27


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