Expert Discusses Key Challenges for the Next Generation of Wearables

He says scientists must solve flexibility, power, and drug delivery problems for an emerging class of biochemistry wearables

3 min read
Nanoengineers at the University of California, San Diego have tested a temporary tattoo that both extracts and measures the level of glucose in the fluid in between skin cells.
Nanoengineers at the University of California, San Diego have tested a temporary tattoo that both extracts and measures the level of glucose in the fluid in between skin cells.
Photo: University of California, San Diego

For decades, pedometers have counted our steps and offered insights into mobility. More recently, smartwatches have begun to track a suite of vital signs in real-time. There is, however, a third category of information—in addition to mobility and vitals—that could be monitored by wearable devices: biochemistry.

To be clear, there are real-time biochemistry monitoring devices available like the FreeStyle Libre, which can monitor blood glucose in people with diabetes for 14 days at a time, relatively unobtrusively. But Joseph Wang, a professor of nanoengineering at the University of California, San Diego thinks there’s still room for improvement. During a talk about biochemistry wearables at ApplySci’s 12thWearable Tech + Digital Health + Neurotech event at Harvard on 14 November, Wang outlined some of the key challenges to making such wearables as ubiquitous and unobtrusive as the Apple Watch.

Wang identified three engineering problems that must be tackled: flexibility, power, and treatment delivery. He also discussed potential solutions that his research team has identified for each of these problems.

It’s worth noting that bioassays—which measure the concentration of chemical substances in tissue—are often incredibly complex to perform. Using small, simple wearables to administer them would make it easier for anyone who needs a bioassay done, either for a single test or to monitor their health long-term.

So why aren’t there more wearables capable of this today? First, Wang discussed the fact that while electrochemical devices are almost always bulky and rigid, biology is soft. If you’re going to put a glucose-monitoring wearable on your body, you want it to be small and able to flex and stretch as you move. This is especially important for the elderly, whose skin is more wrinkled and thinner than younger people’s skin.

Wang’s research team has developed wearable platforms that have a lot in common with temporary tattoos. The idea, generally, is to print the wearable circuitry onto a temporary tattoo-like structure and apply the entire thing directly to the skin. Wang demonstrated such wearable tattoos with circuitry that could stretch up to 200 or 300 percent without ripping or breaking. And if a break should occur anyway, the research team is exploring materials that can repair themselves if torn.

Beyond measuring the amount of glucose in sweat for those with diabetes, Wang said it may also be possible to use such a device to monitor sweat alcohol content. The amount of alcohol in sweat corresponds well to blood alcohol content, so a slap-on sweat alcohol bioassay could provide an easy, non-invasive way to continuously approximate blood alcohol content without requiring a person to keep blowing into a breathalyzer. Wang also mentioned research into melanoma-detecting systems that can check for levels of the enzyme tyrosinase in suspicious skin moles.

Power is also an important input for any wearable. A wireless device is no good without power, and the kind of tattoo-like devices Wang discussed would only fit the smallest batteries. He thinks such devices could be powered by what he referred to as biofuels—things like the lactate in human sweat.

More advanced biochemistry wearables could also deliver drugs or chemicals themselves in addition to sensing. Wang called this a “sense/act/treat” approach, where one device would be capable of performing a bioassay and also delivering the drug needed subcutaneously through microneedles. He mentioned U.S. military interest in developing patches for soldiers that could administer multiple drugs as needed depending on what disease or malady the wearable sensor patch detected—though the microneedle solution would be just as useful for anyone needing regular injections of a drug.

The ideas Wang discussed are still far out in some regards, but he and his team have been conducting this research for more than a decade. Some of the ideas they’ve developed have been spun out into companies, such as a mouthguard that can monitor health markers in saliva. That said, Wang notes that one of the major reasons we haven’t seen more biochemistry monitoring devices is simply because the clinical trials required by the U.S. Food and Drug Administration take a long time to complete.

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