Stretch, sense, and innovate: Advances in next-generation strain sensors

The rapid proliferation of wearable technology, aligned with the digital transformation of Industry 4.0 and the emerging paradigm of Industry 6.0, has accelerated the development of intelligent strain sensors. Polymer composite-based strain sensors have attracted significant attention for their ability to convert mechanical deformation into electrical signals with high sensitivity and adaptability to dynamic environments. Although considerable progress has been achieved, strain sensors face challenges such as balancing sensitivity to stretchability, poor dispersion of nanomaterials, and limited durability. Environmental sensitivity, interfacial adhesion, and high fabrication costs hinder their scalability and performance. Wearable strain sensors are still in the prototype stage, and various obstacles in developing integrated and multifunctional strain sensors must be addressed. This review aims to consolidate the fundamental sensing principles, structural innovations, critical design parameters, and multifunctional properties, including thermal management, EMI shielding, and hydrophobicity of polymer-based strain sensors. Finally, the prevailing challenges and prospects in advancing multifunctional strain sensors for wearable smart gadgets and electronic skin are explored. This review not only elucidates the current state-of-the-art polymer-based wearable strain sensor technologies but also envisions future directions, catalyzing transformative advancements in digital health.