Molecular aspects of muco- and bioadhesion: Tethered structures and site-specific surfaces

Mucoadhesive: controlled-release devices can improve the effectiveness of a drug by maintaining the drug concentration between the effective and toxic levels, inhibiting the dilution of the drug in the body fluids, and allowi ng targeting and localization of a drug at a specific site. Acrylic-based h ydrogels have been used extensively as mucoadhesive systems. They are well suited for bioadhesion due to their flexibility and nonabrasive characteris tics in the partially swollen state, which reduce damage-causing attrition to the tissues in contact. Crosslinked polymeric devices may be rendered ad hesive to the mucosa. For example, adhesive capabilities of these hydrogels can be improved by tethering of long flexible chains to their surfaces. Te thering of long poly(ethylene glycol) (PEG) chains on poly(acrylic acid) hy drogels and their copolymers can be achieved by grafting reactions, or by c opolymerization in the presence of several PEG-containing acrylates. The en suing hydrogels exhibit mucoadhesive properties due to enhanced anchoring o f the chains with the mucosa. Theoretical calculations can lead to optimiza tion of the tethered structure. Experimental results indicate that the chai n interpenetration is a strong function of the PEG molecular weight, the po lymer swelling ratio and the mucosa composition. (C) 2000 Elsevier Science B.V. All rights reserved.