Figure 1: Prosthetic skin based on site-specifically designed SiNR electronics.

(a) Photograph of a representative smart artificial skin with integrated stretchable sensors and actuators covering the entire surface area of a prosthetic hand. Scale bar, 1 cm. The inset shows the artificial skin stretched ~20%. Scale bar, 1 cm. (b) An exploded view of the artificial skin comprised of six stacked layers. Interconnected wires of each layer relay signals to external instruments. (c) Representative microscopic images of SiNR strain gauge: S1 which has a curvature of 0 mm⁻¹ (left); S6 which has a curvature of 10 mm⁻¹ (right). S1 and S6 are optimized for the location of minimal stretch (~5%) and large stretch (~30%), respectively. Scale bar, 10 μm. (d) Representative microscopic images of SiNR pressure sensor S6 and temperature sensor S6. (e) Microscopic image of humidity sensor. Scale bar, 2 mm. Bottom right inset shows the magnified view of the central area, showing separate electrodes with identical inter-spiral gap. Scale bar, 0.5 mm. (f) Microscopic image of electroresistive heater. Scale bar, 4 mm. (c–f) The upper right insets of each figure show the cross-sectional structure of each device. (g) Scanning electron microscope image of the SiNR transferred on the silicon oxide substrate. The wrinkles are deliberately formed to show the SiNR’s high flexibility. Scale bar, 20 μm. (h) The magnified view of wrinkled SiNR. Scale bar, 2 μm. (i) A cross-sectional transmission electron microscope image of the strain gauge, showing that the SiNR encapsulated with PI layers is located at the neutral mechanical plane. Scale bar, 200 nm. Press., pressure; temp., temperature.