Human pulsewave monitoring skin patches, based on flexible and porous PZT/PDMS nanocomposites with improved nanoparticle dispersion

Abstract

This thesis presents a flexible piezoelectric pressure sensor (FPPS) based on a porous nanocomposite with improved nanoparticle dispersion, enhanced vapor permeability, and stabilized metal deposition for precision pulsewave monitoring. First, the nanocomposite dispersion is improved by mixing the glycidyl silane-functionalized piezoelectric nanoparticles with the nonionic surfactant Triton-added polydimethylsiloxane to reduce inter-particle surface energy. Second, the porous piezoelectric nanocomposite with vapor permeability enhancement (≈485 g m$^{–2}$ day$^{–1}$) 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 (≈432 g m$^{–2}$ day$^{–1}$), enabling long-term attachment 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 of 0.999, a hysteresis error of 1.35%, and a stable durability over 200,000 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 pulsewave 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.