Chitosan [a (1----4) 2-amino-2-deoxy-beta-D-Glucan] is a unique polysaccharide derived from chitin. Several attempts have been made to use this biopolymer in biomedical field. The use of this material in the development of hemodialysis membranes, artificial skin, drug targetting and other applications are discussed. It appears, this novel biomolecule, biodegradable, and biocompatible, find applications in substituting or regenerating the blood/tissue interfaces. This polysaccharide having structural characteristics similar to glycosaminoglycans, seems to mimic their functional behaviour.
A new sustained-release dosage form of nitrofurantoin (NF) as microcapsules has been prepared by a mild chitosan/calcium alginate microencapsulation process. These microcapsules have been prepared by adding, dropwise, a solution of sodium alginate containing NF into a chitosan-CaCl(2) system. About 70-80% of the drug is released into phosphate buffer, pH = 7.4 within 6 h. Drug release into the gastric medium is found to be relatively slow compared to that into the intestinal medium. From scanning electron microscopic studies, it appears that the chitosan modifies the NF-alginate microspheres. These findings suggest the possibility of modifying the formulation to obtain the controlled release of NF in an oral sustained-delivery system.
A bioartificial pancreas, a medical device entrapping islets of Langerhans (islets) in an immunoisolative membrane, has been regarded as one of the most promising approaches to treat insulin-dependent diabetic patients. In this study, various modifications of alginate-chitosan microcapsules were made such as the inclusion of polyethylene glycol (PEG) and the use of crosslinkers such as carbodiimide (EDC) and glutaraldehyde (GA) in the core and onto the microcapsule membrane surface. A characterization of the modified microcapsules in terms of mechanical stability and albumin diffusion as well as their surface properties using SEM was performed. A mild GA treatment greatly enhanced the mechanical stability of the microcapsules, and this treatment did not affect the coating process of chitosan or PEG. The biological response to such microcapsules was evaluated by microencapsulation of red blood cells (RBC) and subsequent observation of their hemoglobin release. The encapsulated RBC in the PEG-GA coated microcapsules were found to be less hemolytic and had improved stability and biocompatibility. The results suggest the possibility of developing biological assist organs by microencapsulation of mammalian cells such as islets or liver cells in immunoisolative microcapsules in the near future.
A mild chitosan/calcium alginate microencapsulation process, as applied to encapsulation of biological macromolecules such as albumin and insulin, was investigated. The microcapsules were derived by adding dropwise a protein-containing sodium alginate mixture into a chitosan-CaC12 system. The beads containing a high concentration of entrapped bovine serum albumin (BSA) as more than 70% of the initial concentration were achieved via varying chitosan coat. It was observed that approximately 70% of the content is being released into Tris-HC1 buffer, pH 7.4 within 24 h and no significant release of BSA was observed during treatment with 0.1M HC1 pH 1.2 for 4 h. But the acid-treated beads had released almost all the entrapped protein into Tris-HC1 pH 7.4 media within 24 h. Instead of BSA, the insulin preload was found to be very low in the chitosan/calcium alginate system; the release characteristics were similar to that of BSA. From scanning electron microscopic studies, it appears that the chitosan modifies the alginate microspheres and subsequently the protein loading. The results indicate the possibility of modifying the formulation in order to obtain the desired controlled release of bioactive peptides (insulin), for a convenient gastrointestinal tract delivery system.
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