A new type of electrode made from sugar could help doctors and researchers more effectively monitor contractions during preterm labor, a condition that precedes almost half of preterm births and is the leading cause of US neonatal deaths.
The sensors, developed by engineers at the McKelvey School of Engineering at Washington University in St. Louis, Missouri, could help us understand why some patients experience preterm labor, improve medical interventions, and save lives. In the experiment, the researchers built an array of the new electrodes and successfully tested it on a pregnant person in a lab.
The goal is a home-monitoring belt that is comfortable enough for patients to wear and accurate enough to be clinically useful. Built off a framework of sugar and conductive polymers, the thin electrodes have a sponge-like quality that allows them to hold more gel than standard electrodes, measure for 3 hours instead of 1, and resist artifacts created by patient movement. When tested on a pregnant woman, the new electrodes picked up clean signals even when the patient moved, said electrical engineer and article co-author Chuan Wang, PhD.
There is current technology that exists to monitor and map contractions during early labor, but the tests require hundreds of wire electrodes. Patients must sit still for half an hour while the electrodes are applied, and then remain immobile for the test itself, which has a high sensitivity to movement.
“It’s very uncomfortable. In the clinical setting, the recording typically lasts for 15 minutes to half an hour. During that time, doctors want the patient to be still,” said Wang. “If the patient has to move, it’s going to introduce some artifacts, which is going to ruin the imaging process.”
Wang and colleagues wanted to develop an inexpensive new electrode that would be more comfortable for patients to wear for longer periods of time, yet sensitive enough to detect electrical signals in the body during preterm labor.
To do this, they used sugar structures to create a pliable electrode with a spongy structure. The new electrodes have micropores that hold conductive gel, increasing the amount of electrified surface area touching the skin.
“With the porous structure, we are effectively increasing the area by many, many times,” Wang said. “Because all those voids also contact the skin, increasing the contact area can boost the strength of the signal.”
With conventional electrodes, the gel dries quickly on the flat surface, causing signal quality to plummet. But the new electrodes can be used for “many hours” before drying out, according to Wang.
Additionally, the soft material of the new electrode acts “like a buffer” that absorbs motion and prevents the electrode from sliding around, according to Wang. That means patients can move while wearing the spongy electrodes, without disturbing the recording of electrical signals in the body.
From Sugar Cube to Spongy Electrode
To create the new electrode, the researchers began by molding sugar into an electrode-shaped template. The template was then dipped into a liquid polymer, which oozed in between the grains of sugar. Next, the template underwent oven curing, emerging as a solid yet spongy structure. Hot water was then applied to dissolve the sugar.
The sugar structure is useful here because of the negative space around the grains, which is filled by the polymer — and then because of the negative space left when the sugar dissolves.
“When the sugar grains are removed, that’s where the pores are located,” Wang explained.
The sponge surface was then converted from hydrophobic to hydrophilic, thanks to an oxygen plasma treatment. Next, the sponge was blanketed in a layer of conductive polymer — a liquid that Wang likens to black ink — transforming it into an electrode. (Without the oxygen plasma step, the sponge wouldn’t have absorbed the conductive material.) After another oven-curing session, the device was affixed with wires and ready to be used.
The researchers are continuing to refine the concept and hope to develop a wireless wearable device with many spongy electrodes that record signals simultaneously — and that patients can use at home.
In addition to monitoring maternal and fetal health during labor, the researchers say the belt-like device could be used for other types of imaging and diagnosis.
“Depending on the scenario, different signals can be recorded,” Wang said. “It could be an EMG for a pregnant woman, or an ECG for an athlete or a patient with chronic cardiovascular disease that needs monitoring.”
This work was funded by the Bill & Melinda Gates Foundation (INV-005417, INV-035476). The authors acknowledge the Washington University in St. Louis Institute of Materials Science and Engineering for the use of instruments and staff assistance.
ACS Nano. 2022;16:11792-11801. Full text