Thiolated chitosans

In the 1990s, the concept of thiolated chitosans as outstanding biomaterials exhibiting mucoadhesive, permeation enhancing and in situ gelling properties was pioneered. By immobilizing sulfhydryl bearing moieties on chitosan, thiolated chitosans are generated. An improvement in mucoadhesive properties of these biopolymers is provided by the formation of disulfide bridges with mucus glycoproteins. The permeation enhancing effect of thiolated chitosans is approximately 80-fold higher in comparison to unmodified chitosan. In situ gelling properties, efflux pump inhibition and controlled drug release are among further favorable properties of thiolated chitosans. The dynamic viscosity of thiolated chitosan in the presence of hydrogen peroxide, for instance, is more than 16, 000-fold augmented. Moreover, the potential of thiolated chitosans was proven by various in vivo studies. An absolute bioavailability of 7.24% of nasally administered insulin, for instance, could be obtained using thiolated chitosans as drug carrier matrix, whereas no drug uptake at all was observed in the case of unmodified chitosan. Within this review, the method of synthesis and characterization of seven established thiolated chitosans as well as various formulation approaches such as matrix tablets and micro-/nanoparticles of thiolated chitosans are highlighted.