An overview of composite structural engineering for stretchable strain sensors

Stretchable strain sensors that can be attached to the human body to respond to various strains and convert mechanical stimuli into readable digital signals have attracted immense attention. High sensitivity and excellent mechanical properties are required to capture subtle strains while retaining high stretchability and stability. Composite structural engineering, involving the geometric design and local assembly layout of macroscopic structures, the design and alignment-direction adjustment of microstructures, and the reasonable combination thereof, is an effective strategy for improving the sensing performance of strain sensors and achieving multifunctional integration. Composite structural engineering is broadly divided into natural inspiration and artificial intervention. The present discussion begins from the perspective of composite structural design of active materials and elastic substrates, and selected engineering cases are subsequently described in the order of progressively increasing dimensions. The underlying mechanisms of composite structural engineering are related with change in the Young's modulus or sectional area of substrates, achieving macro-/micro-structural design and high alignment of active materials, and exploiting synergistic effects. Multifunctional integrated devices developed by interdisciplinary intersection, involving mechanical metamaterials, mechanochromic materials, magnetoelectronics, and energy and sensory systems, are summarized. Finally, novel applications, future challenges, and the outlook of stretchable strain sensors are discussed.