New wearable device monitors tumour size

Engineers at Stanford University have created a small, autonomous device with a stretchable and flexible sensor that can be adhered to the skin to measure the changing size of tumours below. The non-invasive, battery-operated device is sensitive to one-hundredth of a millimetre (10 micrometres) and can beam results to a smartphone app wirelessly in real time with the press of a button.

In practical terms, the researchers say, their device — termed FAST for ‘Flexible Autonomous Sensor measuring Tumours’ — represents a new, fast, inexpensive, hands-free and accurate way to test the efficacy of cancer drugs. On a larger scale, it could lead to promising new directions in cancer treatment. FAST is detailed in a paper published in Science Advances.

FAST’s sensor is composed of a flexible and stretchable skin-like polymer that includes an embedded layer of gold circuitry. When stretched the layer of gold develops small cracks that change the electrical conductivity of the material. Stretch the material and the number of cracks increases, causing the electronic resistance in the sensor to increase as well. When the material contracts, the cracks come back into contact and conductivity improves.

This sensor is connected to a small electronic backpack designed by former postdocs and co-authors Yasser Khan and Naoji Matsuhisa. The device measures the strain on the membrane — how much it stretches or shrinks — and transmits that data to a smartphone. Using the FAST backpack, potential therapies that are linked to tumour size regression can quickly and confidently be excluded as ineffective or fast-tracked for further study.

Currently, it’s not unusual for tumours under observation to be measured by hand with metal calipers according to Alex Abramson, first author of the study and a recent postdoc in the lab of Zhenan Bao, the K.K. Lee Professor in Chemical Engineering in the Stanford School of Engineering.

The use of metal pincer-like calipers to measure soft tissues is not ideal and radiological approaches cannot deliver the sort of continuous data needed for real-time assessment. FAST can detect changes in tumour volume on the minute-timescale, while caliper and bioluminescence measurements often require weeks-long observation periods to read out changes in tumour size.

The inherent biological variation of tumours, the shortcomings of existing measuring approaches and the relatively small sample sizes make drug screenings difficult and labour-intensive.

Based on studies with mice, the researchers say that the new device offers at least three significant advances. First, it provides continuous monitoring, as the sensor is physically connected to the mouse and remains in place over the entire experimental period. Second, the flexible sensor enshrouds the tumour and is therefore able to measure shape changes that are difficult to discern with other methods. Third, FAST is both autonomous and non-invasive. It is connected to the skin — not unlike an adhesive bandage — battery operated and connected wirelessly. The mouse is free to move unencumbered by the device or wires and scientists do not need to actively handle the mice following sensor placement. FAST packs are also reusable, cost just US$60 to assemble and can be attached to the mouse in minutes.

One hurdle the researchers had to overcome was the concern that the sensor itself might compromise measurements by applying undue pressure to the tumour, effectively squeezing it. To circumvent that risk, they carefully matched the mechanical properties of the flexible material to skin itself to make the sensor as pliant and as supple as real skin.

“It is a deceptively simple design,” Abramson said, “but these inherent advantages should be very interesting to the pharmaceutical and oncological communities. FAST could significantly expedite, automate and lower the cost of the process of screening cancer therapies.”

Image credit: iStock.com/Dr_Microbe