Programmable and Spatial Stiffness Gradient Substrates for Highly Robust Artificial Skins

Stretchable artificial skins have garnered great interest for their potential applications in real-time human-machine interaction and equipment operation status monitoring. The local stiffer structure areas on the substrates for the functional elements have been verified to improve the robustness of the artificial skins, but it remains challenging to achieve robust sensing performance under mechanical deformation due to large mechanical mismatch and the intricate fabrication process. Herein, we propose an easy strategy for fabricating a substrate with spatial and programmable stiffness gradients to greatly decrease strain interference and increase the robustness under stretching and bending. The substrate was fabricated by direct writing PDMS with laser gelation, where the sensing elements lay on the place with higher stiffness. The modulus of the substrates varied up to 10-fold, and they also show excellent adhesive properties and durability. This configuration of the spatial stiffness gradient effectively inhibits the deformation strain effect of stretching and bending on the sensing elements. Prototype flexible sensors and light-emitting diodes can be integrated into stretchable artificial skins to exhibit highly robust performance during dynamic deformations, demonstrating an efficient pathway for fabricating robust stretchable electronics, especially for real-time health surveillance.