New drug delivery systems based on chitosan.

The development of new delivery systems for the controlled release of drugs is one of the most interesting fields of research in pharmaceutical sciences. Microparticles can be used for the controlled release of drugs, vaccines, antibiotics, and hormones. To prevent the loss of encapsulated materials, the microcapsules should be coated with another polymer that forms a membrane on the surface. In addition there are several fundamental properties of polymers that are useful in solving drug delivery problems, as they can be combined with the drug covalently or ionically to overcome problems like solubility, stability or permeability. Chitosan is a copolymer of N-acetylglucosamine and glucosamine derived from chitin, which is extracted from crustaceans' shells. This polymer has become the focus of major interest in recent years because it has applications in several fields such as biomedicine, agriculture, the textile industry and the paper industry. There are many processes that can be used to encapsulate drugs within chitosan matrixes such as ionotropic gelation, spray drying, emulsification-solvent evaporation and coacervation. Combinations of these processes are also used in order to obtain microparticles with specific properties and performances. This review provides an overview of these four techniques applied directly to chitosan microparticulate systems.