Researchers in Korea have engineered a new patch that makes collecting sweat for biometric data more efficient. Inspired by the way cactus spines collect water, the patch could make daily blood draws a thing of the past for individuals managing diabetes. Developed at the Department of Chemical Engineering at POSTECH in Korea, this technology could also integrate with wearable devices to improve personal health tracking or remote patient monitoring.

The patch relies on Laplace pressure, a phenomenon created by the difference in pressure between the inside and outside of a curved surface. Cactus spines are cone-shaped; to harvest water in arid climates with little to no rainfall, the tip of the spine catches droplets of water from vapor in the air, such as fog or mist. Laplace pressure created by the spine’s conical structure then causes the droplet to travel to the base of the spine to hydrate the plant.  

To take advantage of this process, the researchers mimicked the structure of the cactus spine within a flat model suitable for a skin patch. This involves wedge-patterned collection channels arranged in a circle, like a child’s drawing of the sun. Tiny droplets of sweat collected at the tip move to the biosensor at the wider base of the wedge via Laplace pressure. 

This collection process is fast and efficient, as the wedge-shape transports virtually all of the sweat collected into the sensing area, so none remains inside the collection channel. The research time published their findings in the journal Advanced Materials in August 2021.

Measuring biomarkers in sweat may be able to identify blood glucose levels, making wearable sweat-sensors an potential alternative for the painful finger pricks commonly used for diabetes monitoring. Sweat bioanalytes can also indicate the presence of inflammatory diseases and provide information about stress levels and other important health concerns. 

But so far, sweat collection has remained impractical for wearable monitoring because it requires a certain amount of movement to generate enough sweat to analyze. The new patch can quickly harvest minuscule sweat droplets without the need to induce extra perspiration, bringing continuous, reliable analysis of sweat closer to reality.