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

2. Chitosan And PLGA2.1. Chitosan and Chitosan Microspheres as Controlled DeliverySystemChitosan, a natural linear biopolyaminosaccharide, is obtained by alkaline deacetylation ofchitin, which is the second abundant polysaccharide next to cellulose (183, 184). Chitin is theprincipal component of protective cuticles of crustaceans such as crabs, shrimps, prawns,lobsters and cell walls of some fungi such as aspergillus and mucor. Chitin is a straighthomopolymer composed of β-(1,4)-linked N-acetyl-glucosamine units while chitosancomprises of copolymers of glucosamine and N-acetyl-glucosamine (185, 186, 187). Chitosanhas one primary amino and two free hydroxyl groups for each C 6 building unit.D-GlucosamineN-Acetyl-D-GlucosamineFigure 2.1: Chitosan Chemical StructureDue to the easy availability of free amino groups in chitosan, it carries a positive charge andthus in turn reacts with many negatively charged surfaces/polymers and also undergoeschelation with metal ions (188). Chitosan is a weak base and is insoluble in water and organicsolvents, however, it is soluble in dilute aqueous acidic solution (pH < 6.5), which canconvert the glucosamine units into a soluble form (R–NH + 3 ) (189). It gets precipitated inalkaline solution or with polyanions and forms gel at lower pH. Commercially, chitosan isavailable in the form of dry flakes, solution and fine powder. It has an average molecularweight ranging between 3800 and 2,000,000 and is from 66 to 95% deacetylated (181).Particle size, density, viscosity, degree of deacetylation, and molecular weight are importantcharacteristics of chitosan which influence the properties of pharmaceutical formulationsbased on chitosan. Properties such as biodegradability, low toxicity and good biocompatibilitymake it suitable for use in biomedical and pharmaceutical formulations (189, 190), e.g. it is36