What if wearables like Fitbits and the Apple Watch represent the infancy of on-body health sensors, something we'll one day look back on the way we now look at the clunky, boxy mobile phones of the 1980s? A number of researchers are working on ultrathin, flexible sensors that could be applied to the skin like smart tattoos, or even applied to the surface of organs inside the body to continually monitor vital signs or to deliver time-released drugs. A recent in-depth piece in Nature Magazine looked at the promise, and the many challenges of this kind of technology.

The article starts off with an interview with MC10 scientist John Rogers, also a researcher at the University of Illinois at Urbana–Champaign. MC10's consumer-facing Biostamp, a thin patch that measures heart electrical activity, hydration, body temperature and UV exposure which the company has been working on for at least two years, is set to finally launch in 2016, Nature reports. On the medical side, they're expecting results soon from a neonatal intensive-care unit trial at Carle Foundation Hospital in Urbana, where doctors are using MC10 technology to unobtrusively monitor the vital signs of newborn babies.

Several teams are working on technology similar to MC10's and big companies are very interested, as is the Department of Defense, which invested $75 million in flexible electronics earlier this year. Those technologies face a lot of challenges when it comes to making sensors that are robust, durable, accurate, and safe. But as researchers look at the next step -- implantable sensors beneath the skin and sensors that adhere to organs like the heart and brain, the problems are compounded. The ideal sensor has to be nontoxic and long-lasting, like an external sensor, but also has to be biocompatible, meaning it won't trigger the body's autoimmune response that's always on the lookout for foreign matter.
Michael Strano, a chemical engineer at MIT, is working on this problem and has created a sensor for detecting nitric oxide in blood that worked for 400 days in mice without triggering their immune system. Strano is working with another scientist to go beyond sensors and develop an implantable "pharmacy on a chip" that can "respond to a range of triggers by releasing the appropriate drugs, encased in polymer capsules."

But once electronics are proactive and inside the body, hacking becomes a pretty major concern. So some scientists are working on a truly innovative way for the electronics within the body and within the user's smartphone to communicate with one another. Göran Gustafsson, an engineer at Swedish electronics company Acreo, is leading research into "an in-body intranet that transmits signals at low frequency using the body's water as its wires," the article says. "To send information between devices, or from a device to a smartphone, users must physically touch the objects with their hands. This keeps the signals low-power and private, and avoids clogging up the data-transmitting frequencies that are already squabbled over by mobile phones and wireless routers."

This technology is many years away, owing as much to regulations and risk-averse suppliers as to the lead time for R&D. But some day in the future, your smartphone could be a gateway to much more health information than you can sense from your wrist.