For graphene oxide (GO) composite hydrogels, a two-dimensional GO material is introduced into them, whose special structure is used to improve their properties. GO contains abundant oxygen-containing functional groups, which can improve the mechanical properties of hydrogels and support the application needs. Especially, the unique-conjugated structure of GO can endow or enhance the stimulation response of hydrogels. Therefore, GO composite hydrogels have a great potential in the field of wearable devices. We referred to the works published in recent years, and reviewed from these aspects: (a) structure of GO; (b) factors affecting the mechanical properties of the composite hydrogel, including hydrogen bond, ionic bond, coordination bond and physical crosslinking; (c) stimuli and signals; (d) challenges. Finally, we summarized the research progress of GO composite hydrogels in the field of wearable devices, and put forward some prospects.

    Abstract
    1 Introduction
        1.1 Structure of GO
        1.2 Mechanical properties of GO composite hydrogels
        1.3 Hydrogen bonding
        1.4 Ionic bonding and coordination bonding
        1.5 Physical crosslinking
        1.6 Stimuli and signals
        1.7 Resistance and current type
        1.8 Capacitive type
        1.9 Other
        1.10 Challenge
        1.11 Mechanical properties
        1.12 Water loss of hydrogels
        1.13 Self-healing performance
        1.14 Stability
        1.15 Corrosion of electrode
        1.16 Summary and outlook
    Acknowledgements 
    References

• Senxuan Tang(School of Materials Science and Engineering, Chongqing Jiaotong University)
• Zhihan Liu(School of Materials Science and Engineering, Chongqing Jiaotong University)
• Xu Xiang(School of Materials Science and Engineering, Chongqing Jiaotong University)