Flexible Piezoelectric Pressure Sensors Fabricated from Nanocomposites with Enhanced Dispersion and Vapor Permeability for Precision Pulse Wave Monitoring

Abstract

This research presents a flexible piezoelectric pressure sensor (FPPS) based on a 40 mu m thick nanocomposite with improved nanoparticle dispersion, enhanced vapor permeability, and stabilized metal deposition for precision pulse wave monitoring. First, the nanocomposite uniformity is improved by mixing the glycidylsilane-functionalized piezoelectric nanoparticles with the nonionic surfactant Triton-added polydimethylsiloxane to reduce interparticle surface energy. Second, the porous piezoelectric nanocomposite with vapor permeability enhancement (approximate to 485 g day(-1) m(-2)) is fabricated by dissolving the citrate particles crystallized in the nanocomposite matrix to form uniform pores. The nanocomposites exhibit good piezoelectric properties with vapor permeability higher than the skin perspiration level (approximate to 432 g day(-1) m(-2)), enabling reliable pulse wave monitoring without skin troubles. Third, the crack-free metal films (100/1 nm thick Au/Cr) are deposited directly on the nanocomposite, whose surface adhesion to the metal films is enhanced through the silane functionalization followed by oxygen plasma treatment. The FPPS, achieving those three major advances, shows a resolution of 0.05 kPa, a sensitivity of 9.07 mV kPa(-1), a linearity (R-squared in a regression model) of 0.999, and a stable durability over 200000 pressure cycles within the pressure range of 0.2-20 kPa. The FPPS, making conformal contact with the skin, is sensitive enough to detect subtle systolic/diastolic blood pressure as well as to discriminate pulse wave variations caused by physical activity and vascular aging. Therefore, our research demonstrates that the FPPS has strong potential for applications in individual cardiovascular monitoring and wearable healthcare.