Thiolated Chitosan: A Boon to Ocular Delivery of Therapeutics

Despite numerous scientific efforts many challenges need to be overcome in the ocular delivery because eyes have special and complex anatomic structures. The main problem with the conventional dosage forms is poor ocular bioavailability due to minimum ocular residence time, because of various anatomical and pathophysiological barriers prevailing in the eye. For this reason, much effort has been put into developing nanotechnology-based drug delivery systems to improve ocular bioavailability of drugs by increasing the precorneal residence time. Polymers with thiol groups provide much higher adhesive properties than polymers generally considered to be mucoadhesive. Chitosan and its derivatives are useful polymeric biomaterials that have found a number of applications in drug delivery especially via ocular route. Thiolated derivatives of chitosan known as thiomers produced via immobilization of thiol groups on the primary amino groups of chitosan backbone has improved mucoadhesive properties, permeation enhancement and antiprotease activity. Moreover, it is biocompatible, biodegradable and non-toxic and has mucoadhesion properties by establishment of electrostatic interactions with mucin. Many drugs and therapeutics can be administered via nanoparticulate form or as an in situ gel forming systems through the ocular route using thiolated chitosan. This mini review provides an insight into the various approaches using thiolated chitosan as nanocarriers for ocular drug delivery, summarizes recent findings and its applications in the field of ocular drug delivery.