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• 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]