Wearable devices such as fitness trackers and smartwatches have become popular tools for monitoring one's health. Now, researchers are trying to advance this technology by developing flexible and soft electronic components that can not only offer more comfort but also provide more accurate readings and longer battery life.

Wearable gadgets typically use light-emitting diodes (LEDs) to shine light onto human tissue and a photodiode to capture the returning light. The patterns and intensities of this light can tell us about changes in cardiovascular health. Most existing devices have rigid LEDs and photodiodes set in a hard material like a watch strap. Researchers at Florida State University (Tallahassee, FL, USA) have created a softer, more flexible alternative. They've developed a photodiode that's stretchable and set in an elastic polymer matrix. This design allows the photodiode to fit snugly against the skin without any pressure, offering more reliable measurements of cardiovascular metrics over a longer time.

The work has demonstrated high fidelity measurements and longtime monitoring of heat rate variability and oxygen saturation, potentially enabling next-generation wearable photoplethysmography devices for point-of-care diagnosis of cardiovascular diseases in a more accessible and affordable way. The device could improve diagnosis of cardiovascular diseases and make health care more accessible by providing accurate home testing. Health care systems worldwide are stressed, and accurate at-home testing will result in more resources becoming available to serve the aging population.

“Most health monitoring devices are rigid, but human tissue is soft,” said study co-author Zhibin Yu, an associate professor at the FAMU-FSU College of Engineering. “Our health monitoring system can comfortably adhere to the human body and accurately monitor cardiovascular variables better than what is on the market today.”

“The new photodiode fits securely on the skin because it is soft and pliable like our bodies,” added Pengsu Mao, the study’s lead author. “It gives the user a more precise cardiovascular reading over time.” 

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