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Ti 3 C 2 T x (MXene), a new kind of 2D ceramic nanosheets, is receiving more and more attention in the fields of medicine, biology, energy, electronics, etc. However, the preparation and application of MXene in hydrogel is still in its infancy period. Here, we review the latest progress (after 2018) related to MXene hydrogels in time. Aiming at the key issue of the dispersion stability of MXene in hydrogel systems, the preparation strategy, mechanism, advantages and disadvantages of MXene hydrogels are sorted out in detail, and the potential application prospects of MXene composite hydrogel are introduced. Finally, future viewpoints are put forward for the dispersion stability challenges that need solving in the design of MXene hydrogel. [ABSTRACT FROM AUTHOR]

• MXene can catalyze the ultrafast preparation of hydrogels by redox reaction. • MXene can regulate the internal structure and properties of the hydrogel. • Composite hydrogel has great stretchability (1400%) and recoverability. • Composite hydrogel can be used as a bioelectronic with adjustable adhesion. Re-stacking of 2D Ti 3 C 2 T X (MXene) nanosheets seriously limits their applications and development of effective strategies to overcome this issue remains challenging. Thus, an efficient method was proposed to rapidly fabricate (<20 min) a MXene nanosheets-catalyzed self-assembled, poly-acrylic acid (PAA) hydrogel with excellent conductivity, stretchability (~1400%), and anti-aggregation (>60 d) properties. In the proposed strategy, in-situ growth of TiO 2 nanoparticles (NPs) on MXene surfaces could effectively overcome the nanosheets restacking in solvents. Moreover, the reductive TiO 2 @MXene nanosheets not only catalyze the dissociation of the initiator generating sufficient radicals by redox reaction to initiate the ultrafast polymerization of AA monomers without heating, but also cross-link polymer chains (via chemical bonding) to produce hydrogel in a time scale of minutes instead of hours. Therefore, the MXene-catalyzed ultrafast self-assembly design effectively overcame the problem associated with the re-aggregation of nanosheets in hydrogels. More importantly, the structural, mechanical, swelling, adhesive, and conductive performances of the hydrogel could be adjusted by altering the TiO 2 @MXene contents. This strategy should be extended to almost all types of MXene-radical polymerized hydrogels with tunable structures and performances that have potential applications in the field of wearable bioelectronics. [ABSTRACT FROM AUTHOR]