Hydrogel ionotronics

Abstract

An ionotronic device functions by a hybrid circuit of mobile ions and mobile electrons. Hydrogels are stretchable, transparent, ionic conductors that can transmit electrical signals of high frequency over long distance, enabling ionotronic devices such as artificial muscles, skins and axons. Moreover, ionotronic luminescent devices, ionotronic liquid crystal devices, touchpads, triboelectric generators, artificial eels and gel–elastomer–oil devices can be designed based on hydrogels. In this Review, we discuss first-generation hydrogel ionotronic devices and the challenges associated with the mechanical properties and the chemistry of the materials. We examine how strong and stretchable adhesion between hydrophilic and hydrophobic polymer networks can be achieved, how water can be retained in hydrogels and how to design hydrogels that resist fatigue under cyclic loads. Finally, we highlight applications of hydrogel ionotronic devices and discuss the future of the field.

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Fig. 1: Hydrogels as ionic conductors.
Fig. 2: Artificial muscle, skin and axon.
Fig. 3: Optoelectronic devices.
Fig. 4: Hydrogel ionotronic devices.
Fig. 5: Fracture energy.
Fig. 6: Hydrophilic–hydrophobic adhesion.
Fig. 7: Chemistry of hydrogel–elastomer adhesion.
Fig. 8: Water retention.
Fig. 9: Fatigue of hydrogels.

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Acknowledgements

The authors acknowledge financial support from the National Science Foundation Materials Research Science and Engineering Centers (DMR-1420570). The authors thank collaborators at Harvard University and Xi’an Jiaotong University for much of the work reviewed here. In particular, the co-authors of reference 21, C. Keplinger, J.-Y. Sun, C. C. Foo, P. Rothemund and G. Whitesides, helped shape a long view of hydrogel ionotronics.

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Yang, C., Suo, Z. Hydrogel ionotronics. Nat Rev Mater 3, 125–142 (2018). https://doi.org/10.1038/s41578-018-0018-7

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