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Cactus Spine-Inspired Sweat-Collecting Patches: A Painless Solution for Diabetics

A sensor based on this new sweat-collecting patch would enable continuous, non-invasive monitoring of sweat biochemicals like blood glucose.

According to the International Diabetes Federation, around 415 million people or 8.8 per cent of the world lives with diabetes as of 2019. By 2040, this number is expected to rise to 642 million. Because diabetes is a lifelong disease and there has yet to be a cure for it, people suffering from the condition, particularly that of Type 2 diabetes, are advised to adopt healthier lifestyles to control their blood sugar levels.

To measure blood glucose levels, diabetics endure multiple, painful finger pricks every day. To prevent this, scientists have begun to explore other bioanalytes to measure blood sugar, one of which is sweat. Sweat has been widely considered to be an effective fluid for analysing bioanalytes in the body as it is non-invasive and wearable sweat sensors can be made to support constant healthcare monitoring. However, the practical use of sweat sensors has been hindered by irregular and low sweat secretion rates. Consequently, there is an urgent need to find a way to effectively collect sweat secretions.

In a recent study led by Professor Kilwon Cho and Ph.D. candidate Jonghyun Son of POSTECH’s Department of Chemical Engineering, scientists have developed a skin-attachable patch that quickly collects sweat by mimicking the principle behind cactus spines.

Since cacti grow in arid environments, they have adapted to move water droplets that form on the tip of their spines to their base in order to survive. During this process, the fine water droplets move due to the difference in pressure acting on the inside and outside of the curved surface of the water droplet in a phenomenon called the Laplace pressure.

The newly developed patch applies this principle of how cactus spines collect water. Professor Cho and colleagues mimicked the structure of the cactus spine by using wedge-shaped wettability patterns with superhydrophobic/superhydrophilic surfaces. The design allows sweat droplets on the wedge-patterned surface to spontaneously move to the wide end of the wedge pattern because the Laplace pressure difference between the front and back surfaces of the droplet is maximised. The wedge-patterned channel can also collect sweat quickly and spontaneously regardless of the inclination of the microfluidic channels and without applying additional force.

Furthermore, the patch demonstrated remarkable sweat-collecting efficiency as it transported nearly all the sweat droplets to the sensing area, leaving minimal traces inside the channel. This enables the patch to collect sweat much faster than the conventional microfluidic channel and non-invasively monitor bioanalytes in the blood in a continuous manner.

“Difficulties in collecting sweat has hindered its use in wearable healthcare devices,” explained Professor Kilwon Cho of POSTECH. He added, “This newly developed patch solves that issue by quickly collecting sweat and facilitating its use in various wearable healthcare devices, including blood sugar monitoring.” [APBN]

Source: Son et al. (2021). Cactus-Spine-Inspired Sweat-Collecting Patch for Fast and Continuous Monitoring of Sweat. Advanced Materials, 33(40), 2102740.