Capillaries in the flexible patch channel your sweat to enzyme-containing biosensors

According to a report in Popular Science, researchers at the University of Illinois have developed a prototype patch that monitors your hydration level.

You stick the flexible patch to your forearm or lower back, where it collects your sweat in in-built capillaries and channels it to four sensor dots in the centre of the patch.

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The dots contain enzymes which react with components of your sweat, causing a colour change.

Capillaries in the patch channel sweat to the central enzyme dots (Photo Rahkendra Ice / A. Koh et al. / Science Translational Medicine)

Capillaries in the patch channel sweat to the central enzyme dots (Photo: Rahkendra Ice / A. Koh et al. / Science Translational Medicine)

The enzymes in the prototype react to your sweat’s pH as well as its concentrations of chloride, glucose and lactate.

The scientists then envisage using a smartphone’s camera to measure the intensity of the colours, with an app analysing the results to determine if you are becoming dehydrated.

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The plan is for the patches to be disposable, with each one able to monitor sweat composition for up to six hours dependent on rate of sweating.

A user would be able to keep track of their hydration and sugar levels and use an electrolyte drink to top up before they started to experience cramping or the bonk.


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Popular Science reports that the patch has been trialled on cyclists riding indoors as well as in an Arizonan sportive.

They stayed attached to the cyclists while they were exercising and the colour change worked. But the scientists still need to develop the smartphone app necessary to analyse the data.

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Field trials are currently underway by a sports drink maker and the US Air Force.

So it’s probably going to be a few years before the research produces a product that is ready for market. But it’s potentially a useful, cheap way of keeping tabs on your hydration status when out riding.