A Prestrained Strategy Enabled Highly Sensitive Strain Sensors for Muscle Strength Assessment.

Achieving high sensitivity of stretchable electronics with a wide working range is essential and challenging. While fundamental strategies using topographic design or introducing microstructures (e.g. wrinkles or cracks) can effectively improve the sensitivity, the strain-response range is still rather limited. Here, we propose a tunable and ultrasensitive piezoresistive strain sensor by leveraging a controllable kirigami design and a prestrained strategy. On the one hand, the kirigami structure enhances the sensitivity and structural stability. On the other hand, the prestrained strategy widens the surface crack to generate highly sensitive and continuous linear responses. This strategy allows general stretchable materials to versatilely realize strain sensors with ultrahigh sensitivity (GF > 1000) and good linearity in the low strain range. As a result, the increased sensitivity and conformability to soft surfaces enable the prestrained strain sensor to identify different body motions and hand grips of varying loads. The high amplitude and recognizable signal waveforms provide essential information in muscle strength assessment. With its general applicability to diverse soft materials, this prestrained strategy overcomes the material and manufactural-level limitations for imparting high sensitivity to various strain sensors, presenting a great potential in the fields of medical monitoring and rehabilitation.