An implantable and versatile piezoresistive sensor for the monitoring of human–machine interface interactions and the dynamical process of nerve repair†
Flexible wearable and implantable piezoresistive sensors have attracted lots of attention in the applications of healthcare monitoring, disease diagnostics, and human–machine interactions. However, the restricted sensing range, low sensing sensitivity at small strains, limited mechanical stability at high strains, and sophisticated fabrication processes restrict the far-reaching applications of these sensors for ultrasensitive full-range healthcare monitoring. In this work, an implantable and versatile piezoresistive sensor was developed from a series of conductive composites. The conductive composites, hydroxyethyl cellulose (HEC)/soy protein isolate (SPI)/polyaniline (PANI) sponges (HSPSs), were prepared by lyophilization of HEC/SPI solution and then in situ polymerization of aniline. The sensitivity, response time, and mechanical robustness of the HSPS sensors were characterized, and they can achieve a gauge factor of −0.29, a response time of 0.14 s, and sensing stability for at least 100 cycles. The HSPS sensors could efficiently work in vivo for 4 weeks for the measurement of stimuli, without severe inflammatory reaction. When the versatile HSPS sensors were attached to different parts of the human body, they could detect a variety of human motions including coughing, bending of fingers and elbow, abdominal breathing and walking. Notably, the HSPS sensors could be used to monitor the nerve repair in rats and the results are highly consistent with the electrophysiological data. At the same time a new score system was developed to evaluate rat nerve repair. These results indicate that the HSPS sensors exhibit good biocompatibility, sensitivity, sensing stability and fast response time. The HSPS sensors can be used not only as implantable sensors in vivo but also for analyzing human body motions. Furthermore, they provide an effective sensor device and a real-time, dynamic method for evaluating nerve repair without damage and death of animals. Hence, HSPSs might have great potential in in vivo detection, monitoring of human–machine interfacing interactions and the nerve tissue engineering field.