Relationship between solubility of chitosan in alcoholic solution and its gelation

A cationic polymer chitosan (CHI) is anticipated to be a potent component i n several dosage forms involving transdermal drug delivery systems (TDDS), Solubility of CHI and its gelation in alcoholic aqueous solutions were inve stigated, Elasticity of the gel containing 3% CHI, 2% oxalic acid, as a cro sslinking agent, and ethanol (EtOH) and/or 1,3-butyleneglycol (BG) was also evaluated by a rheometer. The CHI solubility in the gel was dependent on t he solubility parameters of the mixed solvent. High elasticity was observed in the CHI gel when an alcoholic solvent giving low solubility of CHI was used, A good correlation was found between the gel elasticity and the relat ive gel concentration (=concentration of CHI in gel/solubility of CHI in ge l). Since the polarity of mixed solvents also affected the thermodynamic ac tivities of drugs and penetration enhancers, optimization of the vehicle co mposition for TDDS is important to assure suitable drug efficacy.