wearable electronic sensors
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Wearable electronic sensors hold tremendous promise for improving human health and wellness. That promise already runs the gamut from real-time monitoring of blood pressure and abnormal heart rhythms to measuring alcohol consumption and even administering vaccines.
Now a new study published in the journal Science Advances  demonstrates the promise of wearables also extends to the laboratory. A team of engineers has developed a flexible, adhesive strip that, at first glance, looks like a Band-Aid. But this “bandage” actually contains an ultra-sensitive, battery-operated sensor that’s activated when placed on the skin of mouse models used to study possible new cancer drugs.
This sensor is so sensitive that it can detect, in real time, changes in the size of a tumor down to one-hundredth of a millimeter. That’s about the thickness of the plastic cling wrap you likely have in your kitchen! The device beams those measures to a smartphone app, capturing changes in tumor growth minute by minute over time.
The goal is to determine much sooner—and with greater automation and precision—which potential drug candidates undergoing early testing in the lab best inhibit tumor growth and, consequently, should be studied further. In their studies in mouse models of cancer, researchers found the new sensor could detect differences between tumors treated with an active drug and those treated with a placebo within five hours. Those quick results also were validated using more traditional methods to confirm their accuracy.
The device is the work of a team led by Alex Abramson, a former post-doc with Zhenan Bao, Stanford University’s School of Engineering, Palo Alto, CA. Abramson has since launched his own lab at the Georgia Institute of Technology, Atlanta.
The Stanford team began looking for a technological solution after realizing the early testing of potential cancer drugs typically requires researchers to make tricky measurements using pincer-like calipers by hand. Not only is the process tedious and slow, it’s less than an ideal way to capture changes in soft tissues with the desired precision. The imprecision can also lead to false leads that won’t pan out further along in the drug development pipeline, at great time and expense to their developers.
To refine the process, the NIH-supported team turned to wearable technology and recent advances in flexible electronic materials. They developed a device dubbed FAST (short for Flexible Autonomous Sensor measuring Tumors). Its sensor, embedded in a skin patch, is composed of a flexible and stretchable, skin-like polymer with embedded gold circuitry.
Here’s how FAST works: Coated on top of the polymer skin patch is a layer of gold. When stretched, it forms small cracks that change the material’s electrical conductivity. As the material stretches, even slightly, the number of cracks increases, causing the electronic resistance in the sensor to increase as well. As the material contracts, any cracks come back together, and conductivity improves.
By picking up on those changes in conductivity, the device measures precisely the strain on the polymer membrane—an indication of whether the tumor underneath is stable, growing, or shrinking—and transmits that data to a smartphone. Based on that information, potential therapies that are linked to rapid tumor shrinkage can be fast-tracked for further study while those that allow a tumor to continue growing can be cast aside.
The researchers are continuing to test their sensor in more cancer models and with more therapies to extend these initial findings. Already, they have identified at least three significant advantages of their device in early cancer drug testing:
• FAST is non-invasive and captures precise measurements on its own.
• It can provide continuous monitoring, for weeks, months, or over the course of study.
• The flexible sensor fully surrounds the tumor and can therefore detect 3D changes in shape that would be hard to pick up otherwise in real-time with existing technologies.
By now, you are probably asking yourself: Could FAST also be applied as a wearable for cancer patients to monitor in real-time whether an approved chemotherapy regimen is working? It is too early to say. So far, FAST has not been tested in people. But, as highlighted in this paper, FAST is off to, well, a fast start and points to the vast potential of wearables in human health, wellness, and also in the lab.
 A flexible electronic strain sensor for the real-time monitoring of tumor regression. Abramson A, Chan CT, Khan Y, Mermin-Bunnell A, Matsuhisa N, Fong R, Shad R, Hiesinger W, Mallick P, Gambhir SS, Bao Z. Sci Adv. 2022 Sep 16;8(37):eabn6550.
Stanford Wearable Electronics Initiative (Stanford University, Palo Alto, CA)
Bao Group (Stanford University)
Abramson Lab (Georgia Institute of Technology, Atlanta)
NIH Support: National Institute of Biomedical Imaging and Bioengineering