Flexible Strain Sensors Based on Direct-Writing VO₂ Nanobelts Inks for Monitoring Human Motions and Human–Machine Interaction

Flexible strain sensors have attracted extensive attention due to their promising applications in wearable electronics and artificial intelligence, and VO 2 smart materials have been applied in this field due to their sole stimuli-response. In addition, the direct writing method is very facile for the preparation of flexible sensors. Herein, the VO 2 (B) nanobelts with the width ranging from 100 to 200 nm were synthesized by the hydrothermal method in this work. Subsequently, VO 2 (B)-based flexible sensors were prepared via the direct-writing strategy, where the conductive ink containing synthesized VO 2 (B) powders was patterned on the different substrates by pen or brush. The sensors exhibited high sensitivity (GF = 470) and excellent stability (stretch–release cycles more than 1000) and can accurately monitor varieties of human health signals (respiration, pulse, muscle state, etc.). As-prepared smart integrated glove associating with LEDs and power supply can effectively achieve gesture recognition and a primary human–computer interaction model. Furthermore, the sensing signals of joint movements were collected by VO 2 (B)-based flexible sensors and then remotely transmitted to the smart terminal through a wireless local-area network, which achieved real-time monitoring of human movement. Therefore, this work demonstrated the potential application of a VO 2 (B)-based conductive ink in wearable electronic devices and human–computer interaction systems.