The proposed sensor aims to help patients who suffer from muscle atrophy monitor changes to their health in a more convenient way. (Image: Getty Images)

Physicians currently rely on MRI to assess whether a patient’s muscle size and volume have deteriorated, but frequent testing can be time-consuming and costly. However, a new study — from researchers at The Ohio State University and published in the journal IEEE Transactions on Biomedical Engineering — suggests that an electromagnetic sensor made of conductive “e-threads” could be used as an alternative to frequent MRI monitoring.

The team fabricated 3D-printed limb molds and filled them with ground beef to simulate the calf tissue of an average-sized human subject. The findings showed that they were able to demonstrate the sensor could measure small-scale volume changes in overall limb size and monitor muscle loss of up to 51 percent.

“Ideally, our proposed sensor could be used by health care providers to more personally implement treatment plans for patients and to create less of a burden on the patient themselves,” said lead author Allyanna Rice.

The work — the first known approach to monitoring muscle atrophy using a wearable device — builds on Rice’s previous research in creating health sensors for NASA. The space agency is interested in monitoring the health of astronauts in a variety of ways.

“Our sensor is something that an astronaut on a long mission or a patient at home could use to keep track of their health without the help of a medical professional,” she said.

Rice and co-author Asiminia Kiourti designed the device to work by employing two coils as well as a conductor made of e-threads that run along the fabric in a distinct zig-zag pattern.

Though the final product resembles a blood pressure cuff, Rice said it was originally a challenge to find a pattern that would allow for a wide range of changes to the size of the sensor’s loop so it would be able to fit a large portion of the population.

“When we first proposed the sensor, we didn’t realize that we would need a stretchable material until we realized that the person’s limbs were going to be changing,” she said. “We need a sensor that can change and flex, but it also needs to be conformal.”

Though the wearable is still years away from implementation, the study notes that the next major leap would most likely be to connect the device to a mobile app. Also, Rice is looking forward to combining the sensor with other kinds of devices for detecting and monitoring health issues, such as a tool for detecting bone loss.

“In the future, we would like to integrate more sensors and even more capabilities with our wearable,” Rice said.

Here is a Tech Briefs interview, edited for length and clarity, with Rice.

Tech Briefs: What inspired your research?

Rice: Our work is funded by a NASA Space Technology Graduate Research Opportunities Fellowship. Initially, we were focused on finding solutions for the variety of health issues that astronauts face during long-duration space travel. Astronauts experience significant muscle atrophy in a short period of time during missions because of the microgravity environment.

Our goal was to design a lightweight, portable, and wearable sensor for monitoring muscle atrophy on a frequent basis. Of course, muscle atrophy also occurs in patients on Earth suffering from a variety of conditions including cancer, aging, neurological disorders, or long-term stays in the ICU. Thus, we aimed to develop a sensor that could fit a majority of the general population and several use cases.

Tech Briefs: What were the biggest technical challenges you faced?

Rice: The biggest challenge was creating a sensor with a high stretch percentage. Stretchable electronics and conductors are an emerging field that generally relies on liquid- or ink-based materials. We wanted to use conductive threads (e-threads) since they are seamless and more wearable to the user; however, e-threads are rigid and do not stretch on their own. We designed a new zig-zag stitching pattern with the e-threads on spandex material to achieve a stretch percentage of 43 percent.

Tech Briefs: Can you explain in simple terms how the technology works?

Rice: The system is made from two coils: a transmitter (TX) and receiver (RX). We apply a time-varying current on the transmit coil, which generates a magnetic flux on the transmit coil. A magnetic flux is then induced on the receive coil, and this flux induces a voltage on the receive coil that we can measure.

The induced magnetic flux is dependent on the cross-sectional area of the coils. So, as the circumference of the limb increases, the overall magnetic flux and voltage on the receive coil will increase as well. The e-threads are the “wires” for the device that conduct the current, and the zigzag stitching pattern we have employed helps make the “wires” stretchable.

Tech Briefs: Do you have any set plans for further work/research? What are your next steps?

Rice: We would like to incorporate the muscle atrophy sensor with other sensors for wearable, multi-modality sensing, imaging, and monitoring. We are working on developing additional sensors based on antennas and microwave technology. There is also additional work to be done to improve the muscle atrophy sensor, including adding additional coils to improve accuracy and resolution, accounting for more realistic physiology, and elimination of bulky benchtop measurement equipment.

Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to fruition?

Rice: Don’t be afraid to think big and chase after any interesting ideas. Also, expect lots of trial and error and failures before finally succeeding.