A team of researchers at the Pohang University of Science & Technology in South Korea created a passive sweat collection device that is inspired by cactus spines. The device is intended as a means to collect sweat for biomedical analysis; for instance, to measure glucose levels in patients with diabetes. Having the ability to operate without a power source, the patch can passively collect tiny amounts of sweat efficiently, helping to unlock the potential of sweat analysis technology. Sweat analysis holds enormous promise as a way to diagnose and monitor a variety of diseases. The basic idea is that a patch worn on the skin will non-invasively collect sweat and then analyze it. The technique has many advantages in terms of non-invasive sampling and continuous monitoring, but has so far failed to take off as a viable alternative to sampling other body fluids, such as blood or urine. Part of the problem lies in obtaining enough sweat to analyze without first asking someone to perform activities, such as exercise, that induce profuse sweating. This is hardly convenient, so devices that can maximize the amount of sweat they collect may help the technology to progress to an unobtrusive wearable that can monitor disease without any hassle. To boost the sweat collection efficiency of a wearable patch, the Korean researchers turned to nature for ideas. They were inspired by the spines of cacti, which draw tiny amounts of water from their tip to their base using a process called Laplace pressure, where a pressure differential between the inside and outside of water droplets causes them to move along the spine. This process is highly efficient at collecting small amounts of water, allowing cacti to survive in desert conditions. To exploit the same phenomenon, the researchers created wedge-shaped patterns within the patch, with areas that are hydrophobic and areas that are hydrophilic. The patterns maximize the pressure differential between the front and back of a sweat droplet, and act to funnel sweat away from the skin and into a wearable patch. So far, the researchers have reported that the technology can collect sweat more rapidly than conventional microfluidic channels, something that could potentially allow for continuous monitoring of sweat. “Difficulties in collecting sweat has hindered its use in wearable healthcare devices,” said Professor Kilwon Cho, one of the leaders on the development of the patch. “This newly developed patch solves that issue by quickly collecting sweat and facilitating its use in various wearable healthcare devices, including blood sugar monitoring.” Source
