chitosan and plga microspheres as drug delivery ... - UniCA Eprints

2. Chitosan And PLGAused for hypobilirubinaemic and hypocholesterolemic effects (191, 192), antiacid andantiulcer activities, wound and burn healing properties (193), immobilization of enzymes andliving cell and in ophthalmology (194). Among pharmaceutical applications it has been usedas a vehicle for directly compressed tablets (195, 196, 197), as a disintegrant (197), as abinder (198), as a granulating agent (199), in ground mixtures (200), as a drug carrier forsustained release preparations (201, 202, 203, 204) as well as a co-grinding diluent for theenhancement of dissolution rate and bioavailability of water insoluble drugs (205, 206, 207).Chitosan has been shown to possess mucoadhesive properties (208, 209, 210) due tomolecular attractive forces formed by electrostatic interaction between positively chargedchitosan and negatively charged mucosal surfaces. These properties may be attributed to: (a)strong hydrogen bonding groups like –OH, –COOH (211); (b) strong charges (212); (c) highmolecular weight (213); (d) sufficient chain flexibility (209); and (e) surface energyproperties favoring spreading into mucus (214). The positive charge on chitosan polymergives rise to strong electrostatic interaction with mucus or negatively charged sialic acidresidues on the mucosal surface. Chitosan also shows good bioadhesive characteristics andcan reduce the rate of clearance of drug from the pulmonary system thereby increasing thebioavailability of drugs incorporated in it (215).Chitosan possess suitable properties as a carrier for microsphere drug delivery. Chitosanmicrospheres are the most widely studied drug delivery systems for the controlled release ofdrugs, antibiotics, antihypertensive agents, anticancer agents, proteins, peptide drugs andvaccines.Chitosan microspheres are used to provide controlled release of many drugs and to improvethe bioavailability of degradable substances such as protein or enhance the uptake ofhydrophilic substances across the epithelial layers. Chitosan has also been used as a potentialcarrier for prolonged delivery of drugs, macromolecules and targeted drug delivery. Magneticchitosan microspheres used in targeted drug delivery are expected to be retained at the targetsite capillaries under the influence of an external magnetic field (216). Also, strong interactionbetween cationic microspheres and anionic glycosaminoglycan receptors can retain themicrospheres in the capillary region (216).Reacting chitosan with controlled amounts of multivalent anion results in crosslinkingbetween chitosan molecules. The crosslinking may be achieved in acidic, neutral or basicenvironments depending on the applied method. This crosslinking has been extensively used37