Sweat is an effective body fluid for analyzing different bioanalytes in the body without taking blood samples. A sweat sensor, for example, can reduce discomfort for diabetic patients who repeatedly have to draw blood. It can also be used in wearable devices for daily health care monitoring. Currently, however, the biggest obstacle to the diffusion of these sensors is represented by our own secretion rates, which are irregular and low.
A research team led by Professor Kilwon Cho of the Chemical Engineering Department of POSTECH, Korea, recently developed a dermal patch. The device quickly collects sweat avoiding continuous blood draws. How does? Imitating the principle behind the spines of cacti.
Cacti, which grow in arid environments, move the drops of water that form at the tips of their thorns to the base to survive. During this process, the fine water droplets move due to the pressure difference acting inside and outside the curved surface of the water droplet. A phenomenon called Laplace pressure.
Avoid blood draws thanks to nature
The patch newly developed by the POSTECH research team applied the same principle used by cactus spines to collect water. The scientists achieved this by creating wedge-shaped models with surfaces superhydrophobic/superhydrophilic. With this system, a sweat drop on the wedge-shaped surface spontaneously moves towards the wide end, because the Laplace pressure difference between the front and rear surfaces of the drop is maximized.
The results confirm that these channels engraved on the patch can collect sweat quickly and spontaneously regardless of their inclination, without the need for additional force. Furthermore, the wedge-patterned channel shows great sweat collection efficiency: it transports almost all sweat droplets to the sensing area without leaving much inside the channel. It is much faster than conventional microfluidic channels. This is what allows the patch to continuously monitor the blood without sampling.
Difficulties in collecting sweat have hindered its use in wearable healthcare devices. This newly developed patch solves the problem by quickly collecting sweat and facilitating its use in various wearable healthcare devices, including blood sugar monitoring.
Kilwon Cho, POSTECH
