Inspired by cactus spines, Korean scientists develop sensors that can collect more sweat

When it comes to detecting biomarker chemicals in a person, sweat analysis sensors provide a less painful option than blood sampling. A new wearable sensor takes a unique method to collect sweat, imitating cactus spines.

We have seen some sensors attached to the skin that analyze the wearer’s sweat and detect biomarkers related to blood sugar levels, stress levels and certain diseases. However, unless the person is unusually hot or physically active, collecting sufficient amounts of sweat is often a challenge.

In order to solve this problem, scientists at Pohang University of Science and Technology (POSTECH) in South Korea set their sights on cactus plants.

In the arid environment where they live, cacti need to absorb water where they can find it-this includes water vapor droplets that condense on the tips of their spines. Through a phenomenon called Laplace pressure, these water droplets are attracted inward along the cactus thorns until they reach the “skin” of the plant, where they are absorbed. Laplace pressure is defined as “the pressure difference between the inside and outside of the curved surface that forms the boundary between the gas area and the liquid area”. On the cactus spines-it is narrow at the top and expanding towards the bottom-the ever-increasing contact area produces this effect in the water droplets.

POSTECH’s flat disc-shaped sensor does not use a needle, but uses multiple sweat collection channels that radiate outward from a central reservoir like the spokes of a wheel.

Each channel is made of hydrophobic (water-repellent) material, in which a triangular wedge of hydrophilic (water-absorbing) material is embedded. Since the narrow end of the wedge is located on the outside of the channel and the wide end is located on the inside of the reservoir, it can use Laplace pressure to pull even a small amount of sweat in.

In laboratory tests, the sensor proved to be much more effective than existing microfluidic sweat collection systems, regardless of the tilt of the device.

Professor Kilwon Cho said: “The difficulty of collecting sweat hinders its application in wearable medical devices. This newly developed patch solves this problem by quickly collecting sweat and promotes its use in various wearable medical devices. Use, including blood glucose monitoring.”

A paper on this research was published in the journal Advanced Materials.

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