Despite their importance as components for flexible electronics, most stretchable hydrogels suffer from incomplete recovery after deformation, are prone to failure upon long-term repeated stretching, and cannot be exploited at subzero temperatures because of the freezing of their constituent water. Consequently, strategies for circumventing these drawbacks are highly sought after. This study describes the synthesis of a doubly (chemically and physically) crosslinked hydrogel from gelatin and methacrylic acid and demonstrates the suitability of this material for the fabrication of high-performance stretchable and environment-resistant supercapacitors and strain sensors. The performance of this supercapacitor (areal capacitance = 1,210.2 mF/cm² at a current density of 1 mA/cm², maximum energy density = 158.8 μW·h/cm², maximum power density = 659.5 μW/cm²) was superior to that of most of integrated supercapacitors reported to date and was hardly affected by stretchable, low temperatures, bending, ice-cold water and strong acid/alkali solutions or long-term storage. Additionally, a strain sensor based on the above hydrogel was capable of accurately capturing human body motions when affixed to skin and recognising mouse movement (even in humid environments) after implantation into mouse legs. Our work may pave the way to high-performance stretchable and environment-resistant wearable electronics.

The disruption and reconstruction of the TREM2⁺ tissue resident macrophage (TRM) barrier on the surface of synovial lining play a key role in the activation and "remission" of rheumatoid arthritis (RA), which engender the prediction of this immunologic barrier as a potential driver for the achievement of "cure" in RA. However, strategies to promote the reconstruction of this barrier have not been reported, and the effect of patching this barrier remains unidentified. On the other hand, appropriate piezoelectric stimulation can reprogram macrophages, which has never been exerted on this barrier TRM yet. Herein, we design piezoelectric tetragonal BaTiO₃ (BTO) ultrasound-driven nanorobots (USNRs) by the solvothermal synthesis method, which demonstrates satisfactory electro-mechanical conversion effects, paving the way to generate controllable electrical stimulation under ultrasound to reprogram the barrier TRM by minimally invasive injection into joint cavity. It is demonstrated that the immunologic barrier could be patched by this USNR effectively, thereby eliminating the hyperplasia of vessels and nerves (HVN) and synovitis. Additionally, TREM2 deficiency serum-transfected arthritis (STA) mice models are applied and proved the indispensable role of TREM2 in RA curing mediated by USNR. In all, our work is an interesting and important exploration to expand the classical tetragonal BTO nanoparticles in the treatment of autoimmune diseases, providing a new idea and direction for the biomedical application of piezoelectric ceramics.