As the uptake of most drugs from mucosal membranes is controlled by a passive diffusion process, it is essential to provide on the absorption membrane a concentration gradient as steep as possible representing the driving force for drug absorption. In order to achieve that goal the delivery system has to be kept as long as possible in intimate contact with the absorption membrane, which can be guaranteed by utilizing mucoadhesive drug delivery systems. The mucoadhesive properties of all so far used polymers, however, are quite insufficient in order to guarantee this effect. In contrast to these ‘conventional’ polymers, whose mucoadhesive properties are exclusively based on non-covalent bonds, thiolated polymers or designated thiomers are capable of forming covalent bonds with cysteine-rich subdomains of the mucus gel layer. The bridging structure most commonly utilized in biological systems - namely the disulfide bond - is thereby used. Click on the picture.