Degradable and stretchable bio-based strain sensor for human motion detection.

In recent years, flexible strain sensors have attracted considerable attention for the great application potential in the emerging fields of wearable devices, electronic skin and health monitoring. However, most of flexible strain sensors are nondegradable, and the produced numerous electronic wastes after uselessness will seriously threaten environment and ecology. Herein, we propose a new strategy to fabricate degradable and stretchable bio-based strain sensor using candle soot (CS) particles to construct conductive pathways and chitosan, potato starch (PS), and polyvinyl alcohol (PVA) to form stretchable matrix in the presence of Fe3+ ions. Owing to the formation of multiple hydrogen bonding constructed by chitosan, PS and PVA as well as coordination bonding by Fe3+ ions, the obtained strain sensor showed high elongation at break up to 200% and good fatigue resistance. Furthermore, the firm embedding of the CS particles into the surface of the stretchable matrix endowed the strain sensor with steady sensitivity (gauge factors of 1.49 at 0-60% strain and 2.71 at 60-100% strain), fast response (0.22 s) and good repeatability even after 1000 stretching-releasing cycles. In addition, the strain sensor was successfully applied to detect various human motions including finger and wrist bending, swallowing and pronunciation. Interestingly, after connecting to an Arduino microcontroller circuit with a Bluetooth module, the strain sensor was able to wirelessly detect real-time movements of index finger joints. Different from most previously reported sensors, the prepared strain sensor in this work was completely degraded in 2 wt% CH3COOH solution at 90 °C only within 10 min, thus effectively avoiding the production of electrical waste after the updating and upgrading of the sensors. The findings conceivably stand out as a new methodology to prepare environmental-friendly sensors in the field of flexible electronics, which is very beneficial for the sustainable development of environment and society.

Skin-inspired flexible and high-performance MXene@polydimethylsiloxane piezoresistive pressure sensor for human motion detection.

In recent years, flexible high-performance piezoresistive pressure sensors have attracted considerable attention for the important application potential in the emerging fields of smart robots, wearable electronics and electronic skin. Herein, inspired by human skin, a new strategy was proposed for the fabrication of a double-layer piezoresistive pressure sensor with wide sensing range and high sensitivity. It was based on the utilization of sandpaper as template and MXene for the constructions of micro-protrusion rough surface on polydimethylsiloxane film and electrically conductive pathways, respectively. The prepared sensor demonstrated high sensitivity of 2.6 kPa-1 in wide linear range of 0-30 kPa, fast response/recovery time of 40/40 ms and excellent repeatability. Importantly, the sensor was successfully applied for the real-time detection of radial artery heart rate, limb movement, handwriting and vocal cord vocalization. Moreover, the integrated device by the sensors had the capability of identifying and visualizing spatial pressure distribution. The findings conceivably stand out a new methodology to prepare flexible high-performance piezoresistive pressure sensors for wearable electronics, human-computer interaction, intelligent robots and health monitoring.