Fig. 2: Characteristics of the WPPFM and neural interface electrodes.

a Schematic of WTSA. b, Block diagram of WPPFM and neural interface electrodes. c, Wireless power transfer characteristic by matching the resonant frequency at 13.56 MHz. d, e The photographs (left) and the resistance change (right) while pressing the tactile sensor with rod (diameter of 2 mm or 20 mm) according to the existence of a cuboid structure (d; without cuboid structure, e; with cuboid structure). Representative data points are presented whereas standard deviation (SD) are shown as error bars (n = 3). f, g The resistance of tactile sensor (red) and the frequency output of WPPFM (blue) according to the applied pressure (f). The tactile modulated sawtooth pulse signal output from WPPFM according to the pressure applied (g). h Photograph of hydrogel-coated neural interface electrodes. Inset scanning electron micrographs images show the 3D scaffold structure of the hydrogel (red) and the nanostructured surface of the Au-blacked Au electrodes (blue). i Compressive stress–strain curve of the hydrogel. j Electrochemical impedance spectra graph of bare Au electrode, Au-blacked Au electrode, Au-blacked Au electrode with hydrogel.