Wearable Sensor Continuously Measures Subcutaneous Tumor Progression and Regression

October 4, 2022

By Brittany Wade 

October 4, 2022 | A team of researchers from Stanford University and the Georgia Institute of Technology designed a malleable, battery-operated wearable sensor—named Flexible Autonomous Sensor measuring Tumors (FAST)—that continuously monitors subcutaneous tumor progression, regression, and treatment efficacy.  

With the emergence of AI, machine learning, and a bevy of high-throughput screening assays, measuring the efficacy of a cancer drug in vitro is relatively straightforward. Unfortunately, the same cannot be said for tumor monitoring in vivo, a process that continuously poses numerous significant challenges.  

With in vivo inspection, hand-held calipers and other low-resolution measurement tools, small sample sizes, and significant biological variations between research subjects make it difficult to form solid conclusions with any certainty. Furthermore, the process is usually time-consuming and labor-intensive. 

As outlined in a Science Advances paper (DOI: 10.1126/sciadv.abn6550), the research team created a high-resolution and autonomous wearable device that eliminates many of the barriers to successful in vivo tumor monitoring by streamlining the process and offering more detailed information. 

The embedded wearable sensor captures four-dimensional tumor measurements every five minutes and detects size changes down to 10 micrometers. No other non-invasive tumor measuring device provides access to continuous, detailed, and time-dependent data. The sensor runs for 24 hours on a single battery charge and can run indefinitely with adequate battery supply. 

The Gold Standard 

The sensor comprises an elastic polymer—styrene-ethylene-butylene-styrene—coupled with a 50-nanometer layer of gold as an electrical conductor. The flexible polymer allows the sensor to expand and contract based on tumor size.  

“It is a deceptively simple design, but these inherent advantages should be very interesting to the pharmaceutical and oncological communities,” said Alex Abramson, first author and recent Zhenan Bao lab postdoc, in a press release. “FAST could significantly expedite, automate, and lower the cost of the process of screening cancer therapies.” 

As the tumor changes in size, it increases or decreases strain on the sensor, shrinks or widens microcracks in the gold, and creates bends and turns within the sensor that alters the electrical connection. A custom-designed printed circuit board—housed in a “backpack” attached to the research subject—reads the electrical information and wirelessly sends it to a smartphone app. 

In the lab, the sensors were tested on mice to monitor untreated tumor progression. Cancer growth was detected eight days post tumor inoculation with the sensor's resistance measurements accurately correlating with increased tumor size. Next, the team carefully monitored vehicle- and drug-treated mice for tumor regression. FAST detected statistically significant variations in tumor shrinkage within five hours of treatment administration. 

The team also reproduced their findings using standard in vitro methods to ensure accurate sensor readouts. Currently, the device only works with tumors on or near the skin, but the team hopes to develop an implantable version to reach tumors of various shapes, sizes, and depths. 

In its current state, the device enables quick and inexpensive efficacy testing for preclinical drugs, potentially truncating the time frame from research to market. Additionally, real-time access to continuous, high-definition tumor data opens the doors to therapeutic and diagnostic breakthroughs.  

The team proposes that continuous live monitoring could lead to “closed-loop drug delivery platforms,” where the data perfectly synchronizes with drug delivery systems, enabling patients to receive monitoring and proper treatment dosing simultaneously.  

Small, non-invasive, diagnostic wearable devices are taking the biotechnical world by storm. In August, our sister site, Diagnostics World News, published a story about MIT’s wearable ultrasound patch that continuously and independently monitors deep organs for up to 48 hours. With the patch's debut, the MIT team expressed plans to sell the stickers as retail items in big box pharmacies.  

At an estimated cost of just $60 per sensor, the Stanford and Georgia Tech team might follow MIT’s lead in creating a packaged product. Then, one day soon, patients may be able to pick up a prescription, skin care product, and life-saving tumor monitoring device all in one store, creating a new kind of “one-stop shop” for even the most urgent health care needs.