Highly sensitive flexible strain sensor based on microstructured biphasic hydrogels for human motion monitoring

Abstract

Flexible strain sensors have been extensively used in human motion detection, medical aids, electronic skins, and other civilian or military fields. Conventional strain sensors made of metal or semiconductor materials suffer from insufficient stretchability and sensitivity, imposing severe constraints on their utilization in wearable devices. Herein, we design a flexible strain sensor based on biphasic hydrogel via an in-situ polymerization method, which possesses superior electrical response and mechanical performance. External stress could prompt the formation of conductive microchannels within the biphasic hydrogel, which originates from the interaction between the conductive water phase and the insulating oil phase. The device performance could be optimized by carefully regulating the volume ratio of the oil/water phase. Consequently, the flexible strain sensor with oil phase ratio of 80% demonstrates the best sensitivity with gauge factor of 33 upon a compressive strain range of 10%, remarkable electrical stability of 100 cycles, and rapid resistance response of 190 ms. Furthermore, the human motions could be monitored by this flexible strain sensor, thereby highlighting its potential for seamless integration into wearable devices.

Graphical abstract

Keywords

flexible strain sensor / biphasic hydrogel / conductive hydrogel / human motion monitoring

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Authors’ contributions

Xin Gao ― conceptualization, investigation, methodology, and writing-original draft; Xinyu Wang ― conceptualization, investigation, methodology, and writing-original draft; Xingce Fan ― writing-original draft, writing-review & editing, funding acquisition, and supervision.

Declaration of competing interests

The authors declare that they have no competing interests.

Acknowledgements

Xingce Fan acknowledges the China Postdoctoral Science Foundation (Grant No. 2021M700773) and the Jiangsu Planned Projects for Postdoctoral Research Funds (Grant No. 2021K509C). The authors thank Prof. Jiuyang Zhang for the help of experimental tests and fruitful discussions.

Electronic supplementary information

Supplementary materials can be found in the online version at https://doi.org/10.1007/s11706-023-0665-5 and https://journal.hep.com.cn/foms/EN/10.1007/s11706-023-0665-5, which include Figs. S1‒S8 and Tables S1‒S2. Following information is provided: optical images of biphasic hydrogels with SMA percentages of 80% and 90% via emulsion polymerization process; table of components of BH-Xs and G-100%; optical image of pristine and stretched biphasic hydrogels of BH-80%; table of tensile properties of BH-Xs and G-100%; tensile strain–resistance curves of BH-60%, BH-70%, BH-80%, and BH-85%; tensile electrical cyclic curves of BH-80% for 100 times; optical image of tensile test and its setup; optical image of the compressive test and its setup.

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