Development of chitosan sponges for buccal administration of insulin

This paper describes the development of a new highly porous, flexible device for buccal peptide administration by a very simple and mild casting/freeze-drying procedure. It consists of a mucoadhesive chitosan layer containing the peptide drug and an impermeable protective layer made of ethylcellulose. This structure was expected to provide unidirectional drug release to the mucosa and avoid loss of drug due to washout with saliva. Insulin release was modulated by varying some formulation variables (chitosan salt type and Mw, chitosan solution pH, insulin dose). The main factor affecting insulin release was its diffusion across the matrix, this being related to the water uptake/swelling and dissolution properties of chitosan and the viscosity of the gel formed upon hydration. In addition, an electrostatic interaction could occur between chitosan amino groups and the insulin carboxylic groups. Preliminary mucoadhesion studies showed that the affinity of chitosan sponges to mucin surfaces was related to the swelling and solubility properties of the different salts of chitosan.