Dynamic coordination of metal–alanine to control the multi-stimuli responsiveness of self-powered polymer hydrogels

New self-powered hydrogels that reversibly change electrical signals in response to circumambient multiple stimuli are of interest for the development of next-generation smart sensing devices. In this work, a new design of self-powered metallo-hydrogels that show fast self-healing, reversible gel-to-sol transition and multi-stimuli responsiveness, is reported. The hydrogels are cross-linked by dynamic metal–alanine (M–Ala) coordination. Through the assembly of Cu- and Zn-containing hydrogels with a Cu electrode as the cathode and a Zn electrode as the anode, self-powered hydrogels that give electrical signals in response to multiple stimuli are fabricated. External stimuli that are able to vary the binding affinity of Ala ligands (e.g., heating, pH and moisture) or exchange/replace Ala ligands (e.g., chelator) can be used to tune the output electric signals. Our self-powering design strategy combines multi-stimuli responsiveness, flexibility and self-powering in one multi-stimuli responsive soft sensor. It also avoids the high temperature and energy-intensive process during the integration of power sources in sensing devices. This work as a proof-of-concept paves a new way to fabricate self-powered soft biomedical and wearable devices with multi-stimuli responsiveness.