Novel aqueous chitosan-based dispersions as efficient drug delivery systems for topical use. Rheological, textural and release studies

•A novel thiolated chitosan (CTS) useful as topical drug delivery systems is studied.•Theophylline (Th) and Diltiazem (Dt) were chosen as chemically diverse model drugs.•Aqueous dispersions were prepared with 1% or 3% w/v CTS and 0.5% w/v drug.•All flow curves fit the Herschel-Bulkley model with negative yields stress values.•Concentration of CTS and chemical nature of drugs are key factors in drug release. The use of a novel cross-linked thiolated chitosan (CTS) was investigated as the main component of aqueous dispersions (at 1% and 3% w/v) for topical drug delivery systems. The nonionic theophiline (Th) and the cationic diltiazem.HCl (Dt) (at 0.5% w/v concentration) were used as model drugs. All aqueous dispersions behaved as viscoelastic fluids. The CTS 1% dispersions showed predominance of viscous component and low viscosity. However, in the CTS 3% dispersions, both the elastic component and high viscosities prevailed. So, texture parameters improved from CTS 1% to 3% dispersions and CTS 3%-Dt showed greater cohesion and adhesion than CTS 3%-Th, but always below CTS alone. All dispersions showed a Fickian diffusion mechanism. Despite release profiles of both drugs almost fully overlapped at 1% CTS, diffusion coefficients confirmed Dt released faster than Th at 3% CTS. The rheological behavior and the chemical nature of the drugs explained these results.