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Xie, Y., Wang, S., Zhang, Y., Kanai, H., Yamada, K., Wakamatsu, T., Hamada, Y., Obuse, S., Zhang, D., Chu, F., & Ishida, Y. An Anisotropic Hydrogel with Simple Preparation and Well-Defined Structure as a New Platform for Flexible Sensors with Directional Strain and Force Sensing. Materials and Interfaces. 2025, 2(2), 239–249. doi: https://doi.org/10.53941/mi.2025.100019

As a platform to construct the next-generation flexible strain and force sensors, anisotropic hydrogels have recently attracted considerable attention, with an expectation that they would visualize the anisotropic motion of biological systems in a direction-specific manner. To date, a number of anisotropic hydrogels have been developed with an intensive pursuit to improve their practical performance, so that their composition, preparation, and structure have become increasingly complex over the years. In fact, most of these anisotropic hydrogels are prepared from many components including naturally occurring materials, using multiple steps that often require skillful control of kinetic events. Therefore, although some of them show good performances, their complicated and unclear structures make it difficult to elucidate the relationship between structure and properties. As an approach complementary to such trend, here we report a very simple anisotropic hydrogel that would provide a versatile platform for flexible sensors with directional sensing capability. This hydrogel was simply prepared by one-pot reaction from two components, i.e., by magnetic orientation of titanate nanosheet (TiNS) in water and subsequent in-situ formation of a polyacrylamide network. In the resulting hydrogel (TiNS-gel), TiNS platelets were arranged in a lamellar structure with highly oriented, periodic, and homogeneous state. Due to such structure, TiNS-gel exhibited remarkable anisotropy in tensile modulus, nanostructural transformability, and ionic conductivity. Furthermore, TiNS-gel changed its electrical resistance upon tensile deformation, demonstrating its potential utility as a flexible strain and force sensor. TiNS-gel, characterized by easy synthesis, simple composition, well-defined structure, and various anisotropic properties will serve as a useful platform for developing flexible devices with direction-selective strain and force sensing capabilities.

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