New wearable device measures the changing size of tumors below the skin

Stanford University and the Georgia Institute of Technology have developed a small autonomous device that can be attached to the skin to measure changes in the size of cancerous cells. The battery-operated, non-invasive device can measure the size of tumors below one-hundredths of a micrometer (10 micrometers), and transmits results wirelessly to a smartphone app with the touch of a button.

The researchers claim that their FAST device, which is shorthand for Flexible Autonomous Sensor Measuring Tumors, represents a completely new, quick, cheap, hands-free and accurate method to determine the effectiveness of cancer drugs. It could open up new avenues for cancer treatment.

Researchers test thousands of possible cancer drugs each year on mice with subcutaneous tumours. Many do not make it to humans. The process of finding new treatments is slow as technologies to measure tumor regression after drug treatment can take weeks to receive a response. Drug screenings are labor-intensive due to the inherent biological variation in tumors, the limitations of existing measurement approaches, and the small sample sizes.

Alex Abramson is the first author of this study. He was a post-doctoral researcher in the laboratory of Zhenan Bao at Stanford School of Engineering, and now works as an assistant professor at Georgia Tech. It is not ideal to use metal pincer-like instruments to measure soft tissue. Radiological approaches are not able provide the kind of continuous data required for real-time assessment. FAST can detect changes of tumor volume in a minute, while bioluminescence and caliper measurements require long observation periods to determine changes in tumor size.

FAST’s sensor is made of flexible, stretchable skin-like plastic that also includes an embedded layer with gold circuitry. The sensor is connected to an electronic backpack made by co-authors Yasser Kan and Naoji Matsuhisa, former post-docs. The device measures the strain in the membrane, which is how much it shrinks or stretches, and transmits this data to a smartphone. Potential therapies related to tumor size regression can be quickly and confidently excluded using the FAST backpack.



Researchers claim that the device has at least three major advances. The sensor is physically attached to the mouse, and stays in place throughout the experiment. This allows for continuous monitoring. The flexible sensor covers the tumor, making it able to detect changes in shape that would otherwise be difficult to see with other methods. FAST is non-invasive and autonomous. It connects to the skin like a band-aid. Scientists do not have to physically handle the mouse after sensor placement. The mouse can move freely without being restricted by wires or devices. FAST packs can also be re-used, are inexpensive at $60 and can be attached to your mouse in just minutes.

FAST’s flexible electronic materials is the key to this breakthrough. A layer of gold is placed on top of the skin-like plastic material. When stretched, it forms small cracks which alter the material’s electrical conductivity. The electronic resistance of the sensor will increase if the material is stretched. Conductivity increases when the material contracts. Cracks are brought back into contact after the material contracts.

Abramson and Naoji Matsuhisa (an associate professor at University of Tokyo) described how crack propagation and exponential increases in conductivity can mathematically be equated to changes in dimension or volume.

Researchers had to overcome the fear that the sensor might cause damage by applying unduepressure to the tumor, effectively sucking it. They carefully matched the mechanical properties to skin to ensure that the sensor is as flexible and supple as skin.

Abramson states that it is deceptively simple, but has many advantages that should interest the pharmaceutical and oncological community. FAST could greatly expedite, automate, and lower the cost for screening cancer treatments.

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