Rapid Ultratough Topological Tissue Adhesives.

Tissue adhesives capable of achieving strong and tough adhesion in permeable wet environments are useful in many biomedical applications. However, adhesion generated through covalent bond formation directly with the functional groups of tissues (i.e., COOH and NH(2)  groups in collagen), or using non-covalent interactions can both be limited by weak, unstable, or slow adhesion. Here, it is shown that by combining pH-responsive bridging chitosan polymer chains and a tough hydrogel dissipative matrix one can achieve unprecedented ultratough adhesion to tissues (>2000 J m(-2) ) in 5-10 min without covalent bond formation. The strong non-covalent adhesion is shown to be stable under physiologically relevant conditions and strongly influenced by chitosan molecular weight, molecular weight of polymers in the matrix, and pH. The adhesion mechanism relies primarily on the topological entanglement between the chitosan chains and the permeable adherends. To further expand the applicability of the adhesives, adhesion time can be decreased by dehydrating the hydrogel matrix to facilitate rapid chitosan interpenetration and entanglement (>1000 J m(-2)  in ≤1 min). The unprecedented adhesive properties presented in this study open opportunities for new strategies in the development of non-covalent tissue adhesives and numerous bioapplications.