A wearable strain sensor that can measure minuscule changes in the size of tumours in mice has been developed by researchers in the US. The team say that the device could drastically speed up the validation of potential cancer drugs. In trials it was able to detect changes in tumour size of around 10 µm within a few hours of starting treatment with cancer drugs.
Mice with tumours just below the skin are regularly used to test potential cancer drugs, as they have been shown to provide results that are close to clinical outcomes. The efficacy of a prospective treatment is generally determined by observing how these subcutaneous tumours change in size and volume, compared with untreated controls. But the technology for measuring the regression of these tumours is not particularly advanced. They are normally measured by hand with callipers. As well as creating issues with accuracy, this also makes the process time consuming and labour intensive, reducing the volume of drugs that can be tested and the size of trials.
Now Alex Abramson, a chemical engineer who was based at Stanford University when he conducted this research but has since moved to the Georgia Institute of Technology, and his colleagues have developed an elastomeric–electronic strain sensor that could improve the speed and volume of drug testing by providing continuous measurements of tumour size. They note that the real-time, autonomous and accurate tumour monitoring offered by their device could open up new pathways in high-throughput drug screening and basic cancer research.
The sensor – named FAST (flexible autonomous sensors measuring tumours) – consists of a 50 nm layer of gold on top of a styrene-ethylene-butylene-styrene elastomer. When strain is applied to the sensor, microcracks appear in the gold layer, increasing electrical resistance. Resistance in the sensor increases exponentially with strain, and the researchers say that when stretching the sensor, they were able to detect changes of just 10 µm.
The researchers used two cancer models to test the sensors: bioluminescent human lung cancer cells and an A20 B cell lymphoma cell line. After implanting cancer cells under the skin of mice, they measured how the tumours grew and then assessed the tumour response to known therapeutic agents. The strain sensor, a printed circuit board that sends data to a smartphone app and a battery pack were housed in a 3D-printed backpack, attached to the mice using a film dressing and tissue glue. The sensors were pre-stretched to 50% strain, to enable both growth and regression to be measured.
When observing tumour growth for a week, the team found that measurements from the strain sensors were comparable with those from callipers and a luminescence imaging system.
Within 5 hr of treatment starting, the strain sensor was able to detect changes in tumour size compared with untreated mice. This tumour regression was not picked up by bioluminescence imaging or calliper measurements – with these tools, there was no statistical difference between the treated and untreated groups in tumour measurements at the 5-hr time point. Over week-long treatment periods, measurements from the sensor were similar to those from callipers and bioluminescent imaging.
‘Heart-on-a-chip’ process could speed up drug testing
According to the researchers, FAST offers three advantages over other common tumour measurement options, such as callipers, implantable pressure sensors and imaging: it enables continuous tumour monitoring; it can measure changes in size and shape that are difficult to detect with other techniques; and as it is autonomous, it should enable faster, cheaper and larger-scale preclinical drug testing.
“It is a deceptively simple design,” Abramson says, “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.”
The researchers report their results in Science Advances.
