Preparation and characterization of laminated thiolated chitosan-based freeze-dried wafers for potential buccal delivery of macromolecules

This study involves the development and functional characterization of a thiolated chitosan (CS) system for potential buccal delivery of proteins. Thiolated CS was synthesized by conjugating pure CS with thioglycolic acid and dialyzed to remove excess acid. Amount of thiol groups immobilized on CS was determined using L-cysteine calibration curve. The weight average molecular weights of CS and thiolated CS were monitored using gel permeation chromatography. Laminated wafers were obtained by pouring gels (containing bovine serum albumin; BSA, different amounts of glutathione as enzyme inhibitor and mucin to mimic salivary conditions) of the thiolated CS into moulds previously lined with impervious ethylcellulose (EC) films and freeze-dried. The resulting formulations were analyzed using attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD) and scanning electron microscopy (SEM). The formulations were further characterized for functional buccal mucosa performance using hydration, swelling, mucoadhesion and in vitro drug dissolution studies. FTIR showed successful thiolation of CS's amine functionality, CD confirmed that BSA conformation remained unchanged throughout the gel formulation and freeze-drying process, whilst SEM showed a porous microstructure of the wafers and a uniform EC film laminate with no visible pores or cracks. The functional characterization studies showed that glutathione had significant effects on hydration, mucoadhesion and subsequently drug dissolution and release characteristics, whilst mucin affected the mucoadhesive properties of the wafers. It was concluded that BSA-loaded wafers containing 10% w/w glutathione as enzyme inhibitor was the formulation choice for potential buccal delivery and should be selected for further investigations.