New sweatband keeps tabs on body biochemistry

Scientists have developed a sweat-collecting band that can analyse the fluid and determine what’s actually happening inside the body. It could flag up problems we don’t even know we have. So, how does it work? I’ve been speaking with its inventor, John Rogers, at Northwestern University…

John - Many people are familiar with fitness trackers of various sorts, typically mounted on the wrist, measuring steps and overall activity, sometimes heart rate, temperature as well. But it doesn't tell you everything. It doesn't provide any kind of biochemical information on how your body is performing during physical exercise. And so what we were interested in developing is a wrist-worn device that could complement and extend the kinds of parameters that you can currently measure with fitness trackers into this biochemical regime.

Chris - How does it work? What are you actually measuring to get, effectively, from outside the body, a glimpse into what's going on inside the body?

John - When you think of biochemical assessments, you're typically thinking about blood sampling, or maybe more recently measurements of interstitial fluid, the fluid that exists within the tissue but outside of the bloodstream. And there are various ways to capture those fluids and to monitor them, typically in a hospital setting. But the problem with those approaches is they require penetration of the skin, obviously to collect blood but also for interstitial fluid. And those methods are by definition invasive. You have risk for infection, risk for pain, probably not super useful in a routine way for athletes or people who are interested in fitness. And so we focus on sweat because it's very easy to collect, especially during a physical exercise. Everybody sweats and the sweat turns out to have a lot of biomarkers present in it, various biochemical species, many of which correlate with those same species in blood and interstitial fluid. And what we've designed is kind of an elastic band that couples to the skin at the wrist and has little inland ports. And as sweat moves into our band, we can measure different biochemical species and sweat. And we can also determine the rate at which sweat is emerging from the skin. And the total amount of sweat that's released during a given time period.

Chris - Is the rationale for using sweat that we make sweat from blood and therefore it filters out the liquid to make the sweat, and some of these other biomarkers that you're interested in go with the water?

John - That's kind of the idea. The sweat glands are not directly and intimately interfaced with the blood vessels, but there's permeation through the blood into the interstitial fluids, into the sweat glands. And so it's all equilibrating. In many cases, concentrations of species in sweat will be different than those concentrations in blood, but they're correlated. And so in many cases you can establish calibration factors and that's important because there's a tremendous amount of historical data on how to interpret blood serum concentrations of species. That's the chemistry aspect. But like I said, just the physical processes of generating sweat and sweat emerging out of the body, those are important pieces of information to understand as well, especially in athletic performance. You want to avoid cramping and things like that. You'd like to rehydrate. We also have colour changing chemistries to do that chemical concentration measurement just by quantifying the change in colour. The additional colour changing component of these bands allow us to determine the timing at which sweat fills into various parts of the band along its length. And so from that information, we can determine sweat rate as well as total sweat volume. And then in addition for this particular paper, we are demonstrating the ability to determine the lactate concentration in sweat and its pH.

Chris - Have you given it a real road test, or I suppose I should say trackside test? Have you put this into real world settings with real world athletes?

John - We have, in fact. And the publication includes extensive testing on a cohort of human subject volunteers, some of which have high levels of physical fitness, others not so much. The microfluidic band itself is waterproof. And so you can quantify sweat loss and sweat chemistry even when you're in the pool, which turned out to be pretty interesting because I think there's a limited awareness of how much you're sweating while you're swimming because water from the pool is washing the sweat away. And this provides a mechanism for really quantifying that in a way that hasn't been possible in the past.

Chris - If you show this to people, are they showing an interest and are they finding this is actually adding useful data to a training regime that means you can optimise performance further for people.

John - You talk to endurance athletes, you talk to triathlon competitors, you talk to people on our football team. So Northwestern is kind of a small private school, but we have a pretty high level football programme. They monitor sweat currently. The way they do it, however, is with absorbent pads just taped to the surface of the skin. And they use that information to make informed decisions on how much fluid intake they need to consume to get back to where they started. So they're already doing it. The problem is it's a very clumsy process. You aren't able to visualise the release of sweat in real time because you have to take the absorbent pad off and weigh it and wring it out. I think sweat is a whole new kind of metric to think about in the context of your fitness routine. And so I think it will start with performance athletes, but I think there will be much broader interest in this novel way to track your workout.