For the first time, engineers have unveiled an electronic device that closely monitors beating heart cells without affecting their behavior. Specifically, researchers out of Japan have produced a functional sample of heart cells with a soft nanomesh sensor in direct contact with the tissue—an innovation, they say, that paves the way for future embedded medical devices.
When Sunghoon Lee, a researcher at the University of Tokyo, came up with the idea for an ultrasoft electronic sensor that could monitor functioning cells, his colleagues jumped at the chance to use the sensor to study heart cells, or cardiomyocytes, as they beat.
“When researchers study cardiomyocytes in action, they culture them on hard petri dishes and attach rigid sensor probes. These impede the cells’ natural tendency to move as the sample beats, so observations do not reflect reality well,” says Lee. “Our nanomesh sensor frees researchers to study cardiomyocytes and other cell cultures in a way more faithful to how they are in nature. The key is to use the sensor in conjunction with a flexible substrate, or base, for the cells to grow on.”
For this research, collaborators from Tokyo Women’s Medical University supplied a healthy culture of cardiomyocytes derived from stem cells. The base for the culture was a very soft material called fibrin gel. Lee placed the nanomesh sensor on top of the cell culture in a complex process, which involved removing and adding liquid medium at the proper times. This was important to correctly orient the nanomesh sensor.
To make the sensors, first a process called electro-spinning extrudes ultrafine polyurethane strands into a flat sheet—similar to how some common 3D printers work. This spider-web-like sheet is then coated in parylene, a type of plastic, to strengthen it. The parylene on certain sections of the mesh is removed by a dry etching process with a stencil. Gold is then applied to these areas to make the sensor probes and communication wires. And additional parylene isolates the probes so their signals do not interfere with one another.
With three probes, the sensor reads the voltage present at three locations (essentially a cardiogram). Thanks to the multiple probes, researchers can see propagation of signals, which result from and trigger the cells to beat. These signals are known as an action or field potential and are extremely important when assessing the effects of drugs on the heart.
“Drug samples need to get to the cell sample, and a solid sensor would either poorly distribute the drug or prevent it reaching the sample altogether. So, the porous nature of the nanomesh sensor was intentional and a driving force behind the whole idea,” says Lee. “Whether it’s for drug research…or heart monitors, I can’t wait to see this device produced and used in the field.”