Strategies for designing stretchable strain sensors and conductors

Flexible and stretchable electronics are attracting tremendous attention for their enormous future potential in wearable technologies. Flexible and stretchable sensors and conductors are the key components of wearable devices for potential applications such as human motion detection, human health monitoring, and human–machine interfaces. One critical requirement for them is to show high level of wearability (bendability and stretchability) and meanwhile to retain their functionality and reliability under large mechanical deformation. To this end, a wide range of materials and structural designs are developed to construct these sensors and conductors. Here, the recent advances in the development of new piezoresistive materials and microstructural motifs that endow electronics with flexibility and stretchability are summarized. Challenges and future opportunities are discussed in terms of the multimodal and multidirectional sensing capabilities, the trade-off between sensitivity/conductivity and stretchability, multifunctionality, linearity (multiple linear region phenomenon), and integration with flexible power and communication devices.