A strain localization directed crack control strategy for designing MXene-based customizable sensitivity and sensing range strain sensors for full-range human motion monitoring

Wearable flexible electronics are experiencing rapid development for smart life assistance, rehabilitation, and even human enhancement. Owing to the complexity and diversity of wearable and implantable applications, strain sensors with customizable sensing ranges and sensitivities have aroused great interest, while it is still challenging to simultaneously achieve high sensitivity and stretchability. In this work, we report a novel crack design strategy to fabricate sensors for targeted detections via formation of nanocrystal titanium oxide (TiO₂) by means of Ti₃C₂T_x MXene surface oxidation and typical micro- and through-crack pattern sensors for stable large and accurate subtle motion detections are fabricated, respectively. An efficient crack pattern control strategy based on strain localization induced fracture mechanism is proposed. Two typical sensors with a stable sensitivity in a wide sensing range (GF = 1.3 for 0–100% strain) and high sensitivities in small sensing ranges (GF = 530, 3380, 4650, and 75000 in the strain ranges of 0–0.175%, 0.175%–0.45%, 0.45%–3.6%, and 3.6%–5%, respectively) are obtained for large and subtle human motion detection, respectively. This work introduces a new way to fabricate and combinedly use customizable strain sensors for full-range human motion monitoring, addressing the sensitivity-stretchability contradiction issues for conventionally fabricated and solely used strain sensors via strain localization dominated crack control strategy.