text: Various polymers such as poloxamers exhibit in situ gelling properties. Because of these properties they can be administered as liquid formulations forming stable gels once having reached their site of application. An unintended rapid elimination or outflow of the formulation from mucosal membranes such as the ocular, nasal or vaginal mucosa can therefore be avoided. Thiolated polymers are capable of providing a comparatively more pronounced increase in viscosity after application, as an extensive crosslinking process by the formation of disulfide bonds between the polymer chains due to oxidation takes place. This effect was first described in 1999 by Bernkop-Schnürch et al. for polymeric excipients. In case of thiolated chitosan, for instance, a more than 10,000-fold increase in viscosity within a few minutes was shown. These high in situ gelling properties can also be used for numerous further reasons such as for parenteral formulations, as coating material or for food additives