Hierarchical Serpentine-Helix Combination for 3D Stretchable Electronics.

3D stretchable electronics attract growing interest due to their new and more complex functionalities compared to 1D or 2D counterparts. Among all 3D configuration designs, a 3D helical structure is commonly used as it can be designed to achieve outstanding stretching ratios as well as highly robust mechanical performance. However, the stretching ratio that mainly focuses on the axis direction hinders its applications. Inspired by hierarchies in a tendon, a novel structural design of hierarchical 3D serpentine-helix combination is proposed. The structural design constructed by a sequence with repeating small units winding in a helical manner around the axis can enable large mechanical forces transferred down to a smaller scale with the dissipation of potentially damaging stresses by microscale buckling, thereby endowing the electronic components made from high-performance but hard-to-stretch materials with large stretchability (≥200%) in x-, y-, or z-axis direction, high structural stability, and extraordinary electromechanical performance. Two applications including a wireless charging patch and an epidermal electronic system are demonstrated. The epidermal electronic system made of several hierarchical 3D serpentine-helix combinations allows for high-fidelity monitoring of electrophysiological signals, galvanic skin response, and finger-movement-induced electrical signals, which can achieve good tactile pattern recognition when combined with an artificial neural network.