Stability of hydrogel adhesion enabled by siloxane bonds

Abstract

Forming anchoring sites by siloxane bonds at the hydrogel-substrate bonding interface is one of prevailing ways to achieve strong hydrogel adhesion. Considering the hydrolysis of siloxane bonds at the existence of water, we investigate the stability of siloxane bonds enabled hydrogel adhesion in various aqueous environments experimentally and theoretically. Samples of polyacrylamide (PAAm) hydrogel bonded glass substrate by siloxane bonds are prepared and immersed in various aqueous environments, including purified water, acid solution, alkaline solution, and phosphate buffered solution (PBS). We find that the PAAm hydrogel spontaneously detaches from the glass substrate in the alkaline solution for around 1 h and in the PBS for 36 days, but still firmly adheres to the glass substrate in the purified water and acid solution for 36 days. To explain the experimental findings, we incorporate the kinetic theory of bond dissociation with the Lake-Thomas model and get the evolution of hydrogel adhesion with time. By changing the activation energy of siloxane bond hydrolysis, the time required for the catastrophic decrease of hydrogel adhesion can be predicted. This work reveals the failure mechanism of siloxane bonds enabled strong hydrogel adhesion, and might inspire studies on the stability of hydrogel adhesion of other types under the combined effects of mechanical and chemical loads.