Mdo3012

Electric potentials were measured with 30-gauge silver-plated copper wires (Farnell) connected to mixed domain oscilloscope (Tektronix MDO3012). Stimulation electrodes were first positioned in a 2-mm thick PDMS pad for stabilization. Larger electrodes were placed by punching Ø 1mm holes using a biopsy puncher (Ted Pella). Thin measurement electrodes were placed using a 22.1 gauge needle (BD Sciences) to prick the PDMS pad. Stimulation pulses of 50 V were applied using the same equipment as for the ESTIM of the cells; the average height of 6–9 peaks was measured and normalized to the maximum value observed for each paradigm: whole cell or focal stimulation. The measurements for each configuration were performed by changing the positions of the stimulation electrodes without altering the measurement electrodes. Separate pads were used for whole cell (Fig 1C, 1D and 1F) and focal (Fig 1E, 1G and 1H) stimulation paradigms.

The electrospun PI nanofiber membranes on the ITO-PET were used as a friction layer for TENGs. The contact and separation process was conducted by the in-house actuating system controlled via LabVIEW (Supplementary Information Fig. S8a). ITO-PET, which was acted as a collector for the electrospinning process, was used as a bottom electrode for TENGs, and the top electrode was an aluminum tape (Supplementary Information Fig. S8b).
To compare film-like structures and nanofibrous structures, a commercial PI film and a screen-printed PI film were also prepared as friction layers for the TENGs. To fabricate the screen-printed PI film, PI ink with a concentration of 15 wt% was directly screen-printed onto the ITO-PET film using a razor blade and was heated to 60 °C for 3 h. The pressing force was measured with a load cell (UMM-K20, Dacell) and a data acquisition board (PXIe-4330, National Instruments). The electrical performance parameters, including the open circuit voltage (V_OC) and the short circuit current (I_SC), were measured using an oscilloscope (MDO-3012, Tektronix) and a preamplifier (SR570, Stanford Research Systems). The microstructure of the electrospun PI nanofibers was observed using a field-emission scanning electron microscope (FE-SEM: S-4800, Hitachi).

The surface tension of the sacrificial solvents was measured using a surface tension analyzer (DST-60, SEO Co.). To visualize and measure temperature, a thermographic camera (TG-165, FLIR Co.) was used. The microstructure was characterized using field-emission scanning electron microscope (FE-SEM: S-4800, Hitachi Co.). To determine the physical form of the PDMS nanocomposites, X-ray diffraction (XRD: D/Max-2000, Rigaku Co.) analysis was performed. An in-house motorized system controlled via LabVIEW was used to test the TENGs. The contact force of the TENGs was measured using a load cell (UMM-K20, Dacell Co.). The applied contact force was recorded through a data acquisition board (PXIe-4330, National Instruments Co.) mounted on a PXI chassis with a controller (PXIe-8135 and PXIe-1082, National Instruments Co.). For all evaluation of TENGs, the applied force and frequency were fixed to 6 N and 2 Hz, respectively. An oscilloscope (MDO-3012, Tektronix Co.) and a preamplifier (SR570, Stanford Research Systems Co.) were used to measure voltage and current, respectively.