Development of wearable and flexible insole type capacitive pressure sensor for continuous gait signal analysis

In this paper, a porous-polydimethylsiloxane (PDMS) structure was sandwiched between two nylon filter paper based multiwall carbon nanotubes (MWNT) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) composite electrodes for the development of a flexible capacitive pressure sensor for the gait signal analysis. During the fabrication of the porous-PDMS dielectric structure, the composite electrodes were fabricated using a vacuum-filtration method and manually made sugar cube was used as a mold for the formation of a porous structure. The as-fabricated flexible capacitive pressure sensor exhibited 3 different sensitivities of 1.12 MPa−1, 0.86 MPa−1, 0.36 MPa−1 with a fast response time of 1 s. A high stability (>10,000 compression-release cycles), a high R-square of 0.97, and a wide working pressure range (<1200 kPa) were achieved. The fabricated device was also successfully demonstrated as an insole type pressure sensor for real-time gait-signal monitoring. The wearable and flexible capacitive pressure sensor proposed here is highly applicable for numerous healthcare devices and systems.