A Chest‐Laminated Ultrathin and Stretchable E‐Tattoo for the Measurement of Electrocardiogram, Seismocardiogram, and Cardiac Time Intervals

TLDR

Seismocardiography records chest vibrations linked to heartbeats, yet existing SCG sensors are rigid or non‑stretchable, whereas soft electronic tattoos have been used mainly for ECG. This study introduces an ultrathin, stretchable SCG e‑tattoo built from a 28‑µm‑thick filamentary serpentine PVDF mesh. Using 3D digital image correlation to locate optimal placement, the design incorporates paired identical SCG tattoos to cancel motion artifacts and integrates soft gold electrodes into a single EMAC platform that simultaneously records ECG and SCG and extracts cardiac time intervals. The EMAC tattoo demonstrates strong correlations between systolic time interval and systolic/diastolic blood pressures, suggesting a simple, continuous, noninvasive blood‑pressure estimation method.

Abstract

Seismocardiography (SCG) is a measure of chest vibration associated with heartbeats. While skin soft electronic tattoos (e-tattoos) have been widely reported for electrocardiogram (ECG) sensing, wearable SCG sensors are still based on either rigid accelerometers or non-stretchable piezoelectric membranes. This work reports an ultrathin and stretchable SCG sensing e-tattoo based on the filamentary serpentine mesh of 28-µm-thick piezoelectric polymer, polyvinylidene fluoride (PVDF). 3D digital image correlation (DIC) is used to map chest vibration to identify the best location to mount the e-tattoo and to investigate the effects of substrate stiffness. As piezoelectric sensors easily suffer from motion artifacts, motion artifacts are effectively reduced by performing subtraction between a pair of identical SCG tattoos placed adjacent to each other. Integrating the soft SCG sensor with a pair of soft gold electrodes on a single e-tattoo platform forms a soft electro-mechano-acoustic cardiovascular (EMAC) sensing tattoo, which can perform synchronous ECG and SCG measurements and extract various cardiac time intervals including systolic time interval (STI). Using the EMAC tattoo, strong correlations between STI and the systolic/diastolic blood pressures, are found, which may provide a simple way to estimate blood pressure continuously and noninvasively using one chest-mounted e-tattoo.