Flexible electronic “Tattoo” as a dual-signal heart-monitor

January 13, 2020 // By Bill Schweber
Flexible electronic
Researchers from the University of Texas (Austin) Cockrell School of Engineering have fabricated a thin, flexible, stick-on patch for monitoring both conventional electrocardiogram (ECG) signals as well as also-useful seismocardiograph (SCG) readings.

The flexible and comfortable, long-lasting, piezo-driven wearable electronics tattoo (e-tattoo) can be placed on the skin to capture cardiac health-related data in two ways. First, it captures the well-known electrocardiograph readings (ECG or EKG). Simultaneously and time-correlated, it also provides less-known seismocardiograph (SCG) readings. SCG is a measure of chest vibrations associated with heartbeats and provides additional information. When combined with ECG data, it helps assess the accuracy of the ECG readings. “We can get much greater insight into heart health by the synchronous collection of data from both sources,” noted project leader Nanshu Lu, an associate professor in the departments of Aerospace Engineering and Engineering Mechanics and Biomedical Engineering.

The e-tattoo made of polyvinylidene fluoride, a piezoelectric polymer, is remotely powered by a smartphone. The UT team claims it’s the first ultra-thin and stretchable technology to measure both ECG and SCG. Furthermore, although it’s not the first ECG-sensing tattoo, the others are fabricated from non-stretchable materials, making them bulky and uncomfortable for wear beyond short periods. This sensor can be worn for several days while providing constant heart monitoring, a major advantage over brief, “at the doctor” hookups and readings.

Fig. 1: A schematic of the stretchable PVDF e-tattoo (a) and photographs of the e-tattoos unstretched and stretched (b). Source: University of Texas.

The sensing patch consists of a 28-μm-thick polyvinylidene fluoride (PVDF) film with 80-nm thick Cu-Ni electrodes on the top and bottom surfaces. This piezoelectric polymer was patterned into a serpentine mesh by a mechanical cutter plotter for a final mesh size of 38.1x18.1mm. To test the patch itself and establish baseline specifications for applied stress versus resultant strain output, they used a tensile-testing load frame and instrumentation.

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