Paper-Thin Flexible Device Monitors Heart Heath

Pressure sensors made from layers of flexible polymer transistors could one day provide doctors with a safer way to check the condition of a patient's heart.

Developed by researchers at Stanford University (CA, USA), the flexible skin-like monitor, worn under an adhesive bandage on the wrist, is thinner than a US dollar bill and no wider than a postage stamp. The monitor is a combination of a microstructured polydimethylsiloxane dielectric and high-mobility semiconducting polyisoindigobithiophene-siloxane in a monolithic transistor design, which enabled the devices to operate in the sub-threshold regime, where the capacitance change upon compression of the dielectric is strongly amplified.


Functionally, a rubber diaphragm covered with miniature pyramid bumps—only a few micrometers across—forms the thin middle layer of the sensor. When pressure is put on it, the pyramids deform slightly, changing the size of the gap between the two halves of the device. This change in separation causes a measurable change in the electromagnetic field and current flow in the device; the more pressure placed on the monitor, the more the pyramids deform, and the larger the change in the electromagnetic field. When placed on the wrist using an adhesive bandage, the sensor can measure the pulse wave as it reverberates through the body.

The flexible pressure-sensitive organic thin film transistors has a maximum sensitivity of 8.4 kPa(-1), a fast response time of less than 10 ms, a high stability of over 15,000 cycles, and a low power consumption of less than 1 mW. The researchers plan to make the device completely wireless, which could allow doctors to receive the patient's minute-by-minute heart status via a cell phone or other wireless device. The study describing the novel monitor was published in the May 12, 2013, issue of Nature Communications.

“The sensor can be used for noninvasive, high fidelity, continuous radial artery pulse wave monitoring, which may lead to the use of flexible pressure sensors in mobile health monitoring and remote diagnostics in cardiovascular medicine,” said lead author professor of chemical engineering Zhenan Bao, PhD. “For some patients with a potential heart disease, this could be done without interfering with their daily life at all, since it really just requires wearing a small bandage.”

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