While they appear as one homogenous material on the macroscale, hydrogels actually have a very heterogenous structure on the microscale. Studying the structure of hydrogels at this length scale is very challenging, because drying will change the morphology of the gel, and the presence of water precludes the use of standard techniques such as electron microscopy. We have developed a new technique that we call the "Microelectrode Technique" that allows us to probe the local Donnan potential within hydrogels. This method provides us with a means to understand the local microstructure of hydrogels.

Publications:

• Guo, H., Uehara, Y., Matsuda, T., Kiyama, R., Li, L., Ahmed, J., Katsuyama, Y., Nonoyama, T.*, and Kurokawa, T.* “Surface charge dominated protein absorption on hydrogels.” Soft Matter. 2020, 16: 1897–1907.

• Frauenlob, M., King, D.R., Guo, H., Ishihara, S., Tsuda, M., Kurokawa, T., Haga, H., Tanaka, S., and Gong, J.P. “Modulation and Characterization of the Double Network Hydrogel Surface-Bulk Transition.” Macromolecules 2019, 52: 6704–6713.

• Guo, H., Hong, W., Kurokawa, T., Matsuda, T., Wu, Z.L., Nakajima, T., Takahata, M., Sun, T., Rao, P., and Gong, J.P. “Internal Damage Evolution in Double-Network Hydrogels Studied by Microelectrode Technique.” Macromolecules 2019, 52: 7114–7122.

• Guo, H., Kurokawa, T., Takahata, M., Hong, W., Katsuyama, Y., Luo, F., Ahmed, J., Nakajima, T., Nonoyama, T., and Gong, J.P. “Quantitative Observation of Electric Potential Distribution of Brittle Polyelectrolyte Hydrogels Using Microelectrode Technique.” Macromolecules. 2016, 49: 3100–3108.

Hydrogels, due to their high water content, often exhibit low friction on their surface. This is important for in vivo use, as it helps prevent fouling. Recently, some hydrogels have been produced that have extraordinarily high adhesive abilities, a rare trait for hydrogels. Polyampholyte hydrogels that are made up of charged monomers possess a "self-adjustable" adhesive property, where the local ionic bonds can adjust to their surroundings, resulting in adhesion to surfaces of varying charge. Understanding friction and adhesion is important toward the application of hydrogels, especially in biomaterials applications.

Publications:

• Hirayama, S., Kurokawa, T.*, and Gong, J.P. “Non-linear rheological study of hydrogel sliding friction in water and concentrated hyaluronan solution.” Tribology International. 2020, 147: 106270.

• Rao, P.; Sun, T. L.; Chen, L.; Takahashi, R.; Shinohara, G.; Guo, H.; King, D. R.; Kurokawa, T.; Gong, J. P. “Tough Hydrogels with Fast, Strong, and Reversible Underwater Adhesion Based on a Multiscale Design” Advanced Materials. 2018, 30, 32: 1801884.

• Roy, C.K., Guo, H.L., Sun, T.L., Ihsan, A. Bin, Kurokawa, T., Takahata, M., Nonoyama, T., Nakajima, T., and Gong, J.P. “Self-Adjustable Adhesion of Polyampholyte Hydrogels.” Advanced Materials. 2015, 27: 7344–7348.

• Ahmed, J., Guo, H., Yamamoto, T., Kurokawa, T., Takahata, M., Nakajima, T., and Gong, J.P. (2014). “Sliding Friction of Zwitterionic Hydrogel and Its Electrostatic Origin. Macromolecules.” 2014, 47: 3101–3107.

• Yashima, S., Takase, N., Kurokawa, T., and Gong, J.P. “Friction of hydrogels with controlled surface roughness on solid flat substrates.” Soft Matter, 2014, 10: 3192–3199.