Graft Copolymerization Modification Of The Water Insoluble Hemicelluloses And Its Construction Of Drug Delivery System

Hemicellolses are commonly heterogeneous polysaccharides associated with cellulose and lignin in plant cell walls.As the second most abundant biopolymerof biomassfound in nature after cellulose,hemicelluloses are becoming an important sustainable source of polysaccharides for development and application.Owing to their good biocompatibility and biodegradability,hemicelluoses are the kind of ideal materials for preparation of polysaccharide-based hydrogels which have potential applications in tissue engineering and drug delivery.An important characteristic of wis-AGX extracted from corncobs is its ability to remain intact in the physiological stomach environment and small intestine.This property,together with the biodegradability in colonin presence of specific enzymes makesthis copolymer a suitable raw materialfor preparation biopolymers used in the medical field,especiallyas a colon-specific drug carrier.In the last decades,a large number ofdelivery systems were developed with an intention of colon-target drug delivery generallybased on pH-sensitive synthetic polymers or polymer networks.Nevertheless,only a few papers have investigated the properties of xylan and the influence of its characteristics on its application in the pharmaceutical field.Therefore,in this study,a kind of novel pH-sensitive hemicelluloses-based hydrogels aiming to construct a colon-specific drug delivery system was synthesized from the water insoluble hemicelluloses(wis-AGX)extracted from corncobs via sequential graft copolymerization,saponification hydrolysis in alkaline medium and crosslinkage in presence of glutaraldehyde.The chemical structure and morphological structure of the hydrogels were investigated by FT-IR and SEM.The swelling properties of the hydrogels in distilled water and the buffer solutions with different pH(2.0,4.0,7.0,10.0)values were studied,respectively.The results showed that the swelling behavior of the hydrogels exhibited good pH sensitivity due to an obvious volume shrinkage of the gelsin acidic condition and their swellingbehavior in neutral or alkali ones.Furthermore,the swelling ratio of the hydrogels increased with the increase of the-COO-content inthe gels,and decreased with the increment of the crosslinking degree of them.Besides,the significant degradation of the hydrogels was found insimulated colon fluid while it could not be viewed in other fluids including the buffer solutions with pH values of1.2,6.8and7.4 as well as the simulated gastric fluid and intestinal fluid.When the hydrogels were used as drug carriers to entrap theophylline,their drug release behavior exhibited excellent pH sensitivityand time-dependence,because the cumulative percent drug release in pH 7.4 buffer solutions were much higher than thatin pH 1.2 buffer solutions in the same time interval.The controlled release of thehydrogels loaded with an anti-colitis drug 4-ASA were investigated in simulated gastric fluid,intestinal fluid and colon fluid with enzyme action.The cumulative release rates of drug-loaded hydrogels in colon were higher than those in gastric and intestinal and their behavior of drug release showed good pH sensitivity.Therefore,the novel hydrogels were suggested to be an intelligent drug delivery system,which have potential applications in colon-targeted drug release.