Adhesion and Cohesion Differences between Catechol- and Pyrogallol-Functionalized Chitosan

Marine-inspired phenolic compounds that exhibit underwater adhesion are used as biomedical adhesives under wet conditions. While these applications mainly use catechol and pyrogallol moieties that contain different numbers of hydroxyl groups on their benzene rings, how this difference affects adhesion and cohesion is not well understood. Herein, the chitosan backbone is functionalized with catechol and pyrogallol at similar modification rates (to give chitosan-catechol (CS-CA) and chitosan-pyrogallol (CS-GA), respectively) and their interaction energies are compared by using a surface forces apparatus (SFA). The phenolic moieties decrease the rigidity of the chitosan chain and increase solubility; consequently, CS-CA and CS-GA are more cohesive and adhesive than chitosan at pH 7.4. Moreover, the additional hydroxyl group of GA provides a further interacting chance; hence, CS-GA is more cohesive and adhesive than CS-CA. This study provides in-depth insight into interactions involving chitosan derivatives bearing introduced phenolic moieties that will help to develop biomedical adhesives.