Vhb 4905

The biomimetic skin was based on the hydrogel, which is equilibrated in 4 M NaCl with the initial monomer concentration of 45% and the monomer mass ratio (AA: DMAPS) of 4:1. Infrared images of the biomimetic skin were recorded by an infrared thermal camera (FLIR T630SC). The capacitive and resistive signals were recorded on an LCR meter (TH2830) controlled by a LabView program. The LCR meter was used to simultaneously detect capacitance/resistance changes when the hydrogel-based iontronics were stimulated by strain, temperature, and stress. Heating and cooling cyclic tests are performed with a Peltier temperature controller. Unless otherwise stated, we introduced an epidermis-like elastomer (VHB 4905, 3M) to protect the supramolecular skin when measuring capacitance and resistance upon strain, temperature, and stress stimuli^{9 (link)}. Besides, long-term stability of the hydrogel-based iontronics was measured in a BPHJ-120AF temperature and humidity test chamber at the certain condition (Shanghai Bluepard Instruments Co., Ltd).

The device was manufactured using, as a dielectric elastomer membrane, a bi-adhesive acrylic-based elastomer film (VHB 4905, 3M, USA). The membranes were bi-axially pre-stretched, as specified in the following sections. They had an initial unstrained thickness of 0.5 mm, which then reduced to a lower value, depending on the applied pre-stretch, both during manufacturing (as detailed below) and before testing, by acting on the supporting screws (see the main text).

Before coating the polyanion slurry, part of the area of previously prepared CNT@SEBS-IM fiber was covered by a masking tape (VHB 4905, 3M) to disconnect the polyanion and CNT coating layer, forming the channel of IBJTs. Then fibers were immersed in the SSEBS slurry and continuously drawn out by a starching machine, which resulting product was named CNT@SEBS-IM@SSEBS fiber. The coating layer was dried after passing through two 120 °C furnaces and then was further immersed in NaCl solution at 80 °C for the in-situ ion exchange to yield the SEBS-SN polyanion with sodium ions. Following process steps containing washing in deionized water and drying at 120 °C were performed to remove small molecules, the resulting product was named CNT@SEBS-IM@SEBS-SN fiber (Supplementary Fig. 7b).
The SEBS-IM is nearly hydrophobic due to the grafting of hexylimidazolium with a long alkyl chain, while SEBS-SN is hygroscopic; it can absorb up to ~30 wt% of water in ambient conditions. Therefore, we stored SEBS-SN in a desiccator with a drying agent and heated it to 60 °C under a vacuum for 3 h before use. After drying, a small amount of residual water (<2 wt%) was observed in SEBS-SN, as evidenced by ATR-FTIR (Supplementary Fig. 4a) and TGA (Supplementary Fig. 4b). CA tests can also prove this phenomenon (Supplementary Fig. 5).