Flexible strain sensors have attracted great attention and research interest in the fields of medical monitoring equipment, intelligent robots and wearable sensors because they have the flexibility of human skin and can simulate the sensory function of human skin by converting various external stimuli into electrical signals. The flexible strain sensor is mainly composed of active material, stretchable material or flexible substrate/matrix made of deformable material. For the preparation of flexible strain sensors, hydrogels have good biocompatibility, high tensile strength and similar structure to natural soft tissue, making them a good candidate for flexible substrates, especially in the manufacture of tensile, transparent and wearable pressure/strain sensors. How to avoid the swelling of hydrogels during modification and to achieve Janus adjustment of adhesiveness and toughness of hydrogel are the scientific problems that need to be solved urgently for hydrogel strain sensors.
Recently, Prof. Xiaojin Zhang in Fan Xia’s group of China University of Geosciences (Wuhan) proposed a filter paper mediated diffusion to form Janus adhesive-tough hydrogel (Figure 1). First, double-network hydrogel was designed and prepared. Then, the filter paper of absorbing ion or organic small molecule was attached to double-network hydrogel, and the substance diffuses from the filter paper to the hydrogel. This method is simple in operation, and can effectively avoid the swelling of the hydrogel. Finally, the filter paper was removed, and the corresponding structure was designed, which destroyed the double-network structure and produced the adhesive surface, thus obtaining Janus adhesive-tough hydrogel. The depth of the diffusion substance in the hydrogel was controlled by adjusting the filter paper attachment time. The concentration of diffused substances in the hydrogel was controlled by adjusting the concentration of the substance in the filter paper. Lithium chloride was added into the hydrogel during preparation process, which gives the hydrogel conductivity and applies it to strain sensors to detect human motion signals.
Figure 1. Construction of Janus adhesive-tough hydrogel.
This work attempts to explore hydrogel structure and expands the application scope of hydrogels. The article was published in Chemical Engineering Journal under the title "Gold nanoparticles-deranged double network for Janus adhesive-toughhydrogel as strain sensor ".
This research was supported by the National Natural Science Foundation of China and National Key Research and Development Program of China. Prof. Fan Xia and Prof. Xiaojin Zhang from China University of Geosciences (Wuhan) are the corresponding authors of this work.
Article link: https://www.sciencedirect.com/science/article/pii/S1385894721020337
