4D printed multifunctional wearable strain sensors with programmable sensing characteristics

Combining 4D-printed bilayer actuators with the slit structure and sensing capabilities unique to the process further promotes the use of 4D printing in biomedical devices, human-computer interaction, intelligent self-protection devices, and humanoid robots. In this study, we propose an adaptive multifunctional strain sensor (AMSS) 4D printing strategy based on the shape memory properties of polylactic acid (PLA), a bioslit structural sensing unit, and a bi-directional deformation design of a bilayer structure. The obtained AMSS was shown to have excellence sensitivity to strain, mechanical, and temperature stimuli. In particular, thanks to the 3D printed slit structure and phase transition properties of the PLA printing layer, the AMSS macro-microstructure can be precisely tuned, and its sensing performance is shown to be intelligently programmable. The built-in structural design-induced macro-deformation enables AMSS to adaptively fit human joint surfaces for full-range human motion recognition. In addition, the close correlation of strain-sensing during AMSS shape transformation enables position self-sensing and strain self-sensing of AMSS. Further, through the integration and separation of resistive signals, we are able to recognize temperature and mechanical stimuli. Finally, we integrate the wireless sensing module into the AMSS to improve the portability and wearability of the sensor.