| Biodegradable polymers are one of the most important biomedical materials. For the biodegradability in bodies, they are used as biomedical materials, developed rapidly and have an extensive application. This paper briefly reviewed the development of biodegradable polymers, the colon-specific drug delivery systems, the synthesis and the biodegradation of the novel hydrogels used for colon-specific drug delivery.The physiological characteristics of colon make it the best absorptive site for many drugs and the oral colon drug delivery systems are the best approaches for protein, peptide and drugs. Konjac glucomannan (KGM) is water-soluble non-ionic polysaccharides with a high-molecular weight. It is a linear random copolymer of β (1,4) linked D-mannose and D-glucose. The ratio of mannose and glucose is about 1.6:1. Since it can only be degraded by the β-glycosidases existing in colon but not in the upper gastrointestinal (GI) tract, the materials based on KGM can ensure the targeted-release of drugs to colon. Its chemical stability, better biocompatibility, biodegradability and easily modified ability suggest their applications in targeted drug delivery systems. In this paper, two kinds of biodegradable hydrogels which can be used as colon-specific drug delivery were synthesized by using KGM as the structural framework, and the properties of the hydrogels were studied.A novel biodegradable hydrogel was designed to take advantages of biodegradability of KGM and pH-dependence of poly(acrylic acid). The obtained gels are expected to have enhanced site-specificity to colon. In addition, the hydrogels can be prepared in aqueous medium under moderate temperature. We studied the dependence of swelling behavior of the hydrogels on the reaction conditions and pH value of external environment. The degradation of these hydrogels were evaluated under the action of buffer solution, pancreatin and cellulase, respectively. They can just be degraded by cellulase E0240 which contains β-glucosidases. The crosslinking density of the gels and the concentration of the cellulase can both significantly affectthe rate and the degree of the gels' degradation. In order to evaluate hydrogels' potential as colon-specific carriers, the drug release properties of the hydrogels was investigated using 5-aminosalicylic acid(5-ASA) as the model drug. The results of drug release in different conditions showed that the process of drug release was controlled by the swelling and degradation of the hydrogels. In vitro release profile of model drug implies that hydrogels KGM-graft-AAs can be exploited as potential carriers for colon-specific drug delivery.Another novel biodegradable hydrogels based on KGM for colon-specific delivery had been synthesized by crosslinking with sodium tripolyphosphate. The swelling ratio increased with the increasing concentration of konjac glucomannan or the decreasing concentration of sodium tripolyphosphate. The degradation of these hydrogels was evaluated by the reaction of buffer solution, pancreatin, cellulase E0240. The results of in vitro degradation showed that the hydrogel can be degraded rapidly under the specific enzymes of KGM and the ratio of weight loss decreased with the increasing cross-linking density. During the synthesis of the hydrogels, the model drug 5-ASA was loaded. The results of in vitro drug release under the cellulase showed that the process of drug release was controlled by the degradation of hydrogels and the obtained hydrogels can be used as potential carriers for colon-specific drug delivery.In conclusion, the colon-specific drug release of these two drug-loaded hydrgels can be controlled by regulating the hydrogels' swelling behavior and degradation. The obtained hydrogels were potential to be novel materials for colon-specific drug delivery.
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