Sensors based on rose petals could be the fix wearables need to accurately track hydration, scientists say

Sweat sensors are wearable tech that might sound great on paper, but not so much in practice.

Instead of just counting steps or heartbeats, they analyse your perspiration and give you data like hydration levels, electrolyte balance and muscle fatigue. In theory, that means smarter insights into how your body’s really coping with training.

However, the problem is that most current sweat trackers don't actually work that well. For one, they're fiddly. They need to be strapped on tightly with adhesives or sticky patches to stay in place, which can not only get uncomfortable for those wearing them, but they can sometimes cause irritation. Not ideal if you’re wearing one during a long run or a gym session.

Well, researchers at Waseda University in Japan reckon they’ve got the answer and, rather strangely, it takes inspiration from...rose petals.

A sweat sensor that never touches your skin

In a new research paper published in Cyborg and Bionic Systems, the team of scientists unveiled a bio-inspired sweat sensor that doesn’t need to sit directly on your skin, but somehow still delivers stable and accurate readings.

The sensor apparently sits a couple of millimetres above the skin thanks to its clever surface, which mimics the unique micro-texture of rose petals.

If you’ve ever noticed how tiny droplets stick to a petal but larger ones roll straight off, that’s the trick the researchers copied. It means the sensor can cling onto small amounts of sweat to get stable readings, but once things ramp up it “self-cleans” by flushing away the excess.

The research team even moulded actual petals to make two prototypes: one patterned after the inner petals with fine wrinkles, and another based on outer petals with tiny spikes and islands. Both were layered over carbon nanotube membranes, which are already popular in lab-grade sweat trackers, but here it's the petal texture that makes the real difference.

Smarter tracking, fewer sticky patches

To test if their theory worked, the scientists tested the sensor on treadmills after being built into a small 3D-printed wearable with microchannels that funnel sweat to it without ever touching the skin.

They found that it was able to track sodium levels - a marker for hydration and muscle function - reliably across both low and high sweat phases.

What's more, it was found to be super comfortable. There's no sticky adhesives, no irritation, and the self-cleaning design means the sensors are reusable, too.

It's early days, of course, but the exciting thing here is that the researchers claim the same approach could work in smartwatch straps, chest bands or even prosthetics and exoskeletons, feeding real-time hydration and fatigue data into smarter assistance systems.