Integrated design and manufacturing of wearable capacitive sensors embedded in a 3D-printed finger cot for hand gesture recognition

Versatile force sensors have dominated academic research and industries in micro-electro-mechanical systems for many applications over two decades. However, few studies have focused on flexible force-sensing devices that can be wearable directly for users in biosensing applications. In the study, we comprehensively report an integrated design of a flexible force-sensing device comprising a sandwiched-structure capacitive element embedded in a finger cot using a hybrid manufacturing process based on 3D printing. With silicone, graphene, and carbon nanotubes (CNT) prepared for the direct ink writing (DIW) process, the capacitive elements with a zigzag structure were formed from additive manufacturing and bonding with copper foils. At the same time, the finger cot was 3D-printed from photo resin of stereolithography (SLA). When wearing the SLA finger cot integrated with the DIW elements on a human hand, various activities of five hand fingers, such as making a fist, grasping an object, and recognizing different hand gestures, were demonstrated with multiple performances of the force-sensing device. In future studies, the hybrid method (DIW plus SLA) could be further explored with more functional materials and soft structures that would enable the heterogeneous integration of soft robotic devices to fit diverse wearable systems and applications, such as human-machine interfaces and adaptive machining learning.