Unified principle for wet adhesion

Wet adhesion involves wet materials such as hydrogels and biological tissues. Unlike traditional dry adhesion where two materials are dry and can be connected by a dense layer of bonds at the interface, wet materials contain more than 60 wt% of water and water molecules prevent the formation of dense bonds, posing a particular challenge for adhesion. Strong adhesion between wet materials must engage polymer networks. To understand and design adhesion strategies, we surveyed the successful examples and concluded that strong adhesion must elicit chemistry of bonds, mechanics of dissipation, and topology of connection. This principle is generic to any adhesion. In particular, the topology design provides a new insight to connect two materials much beyond chemical bonds, which can be particles, polymers, polymer networks, and their combinations.

Deep adhesion by topological entanglement

Traditional adhesion requires functional groups from adherents to form bonds at the interface. This strategy limits the material choice to match the mechanical properties of tissues. We have pioneered the topological adhesion strategy by diffusing polymer chains into two hydrogels and in situ gelating into a new polymer network, which topologically entangles with the two polymer networks of hydrogels to form adhesion. Because polymer chains penetrate deep into hydrogels, the adhesion is also deep. This may be useful for long-term bioadhesion to combat the extracellular matrix remodeling that may degrade adhesion. This strategy also represents a modular design of bioadhesives, which integrates a liquid adhesive polymer layer and a solid hydrogel layer. The polymer layer provides deep adhesion while the hydrogel layer provides tissue-mimetic mechanical properties. We further design and tailor the chemistry of adhesives to control diffusion kinetics, gelation kinetics, adhesion strength, stability, and on-demand detachment. Part of the research is supported by the NSF CAREER Award.

Relevant papers on this topic
Yang, J., Bai, R., and Suo, Z., 2018. Topological Adhesion of Wet Materials. Advanced Materials, p.1800671
Yang, J., Bai, R., Chen, B. and Suo, Z., 2019. Hydrogel Adhesion: A Supramolecular Synergy of Chemistry, Topology, and Mechanics. Advanced Functional Materials, p.1901693
Yang, J., Bai, R., Li, J., Yang, C., Yao, X., Liu, Q., Vlassak, J.J., Mooney, D.J. and Suo, Z., 2019. Design molecular topology for wet-dry adhesion. ACS Applied Materials & Interfaces, 11(27), pp.24802-24811.
Steck, J., Yang, J. and Suo, Z., 2019. Covalent Topological Adhesion. ACS Macro Letters, 8, pp.754-758. 
Li, J., Celiz, A.D.#, Yang, J.#, Yang, Q., Wamala, I., Whyte, W., Seo, B.R., Vasilyev, N.V., Vlassak, J.J., Suo, Z. and Mooney, D.J., 2017. Tough adhesives for diverse wet surfaces. Science, 357(6349), pp.378-381
Chen, B., Yang, J., Bai, R. and Suo, Z., 2019. Molecular Staples for Tough and Stretchable Adhesion in Integrated Soft Materials. Advanced Healthcare Materials, p.1900810
Steck, J., Kim, J., Yang, J., Hassan, S. and Suo, Z., 2020. Topological adhesion. I. Rapid and strong topohesives. Extreme Mechanics Letters, p.100803
Yang, J., Steck, J., Bai, R., and Suo, Z., 2020. Topological adhesion II. Stretchable adhesion. Extreme Mechanics Letters, p100891
Wang, Y., Jia, K., Xiang, C., Yang, J., Yao, X. and Suo, Z., 2019. Instant, tough, noncovalent adhesion. ACS Applied Materials & Interfaces, 11(43), pp.40749-40757.
Yang, J., Steck, J. and Suo, Z., 2020. Gelation kinetics of alginate chains through covalent bonds. Extreme Mechanics Letters, p.100898