Monitoring the beating heart

Materials World magazine
31 Jan 2019
The sensor probes are formed by a 100nm thick layer of gold as it is resilient and does not interfere with cell chemistry. CREDIT: © 2018 SOMEYA GROUP.

A nano sensor to monitor heart cells with minimal disruption has been developed by Japanese engineers. Katherine Williams reports. 

 Heart cells like to move to the beat. This natural tendency means that studying cardiomyocytes in vitro can prove challenging.

So when Sunghoon Lee, a researcher at the University of Tokyo, Japan,came up with the idea for an ultrasoft electronic sensor that could monitor functioning cells, colleagues jumped at the chance to use this sensor to study cardiomyocytes, as they get into the groove.

Researchers from Tokyo Women's Medical University supplied a healthy culture of cardiomyocytes derived from human stem cells. ‘When researchers study cardiomyocytes in action they culture them on hard petri dishes and attach rigid sensor probes’, explains Lee. 

Unfortunately, ‘These [materials] impede the cells' natural tendency to move as the sample beats, so observations do not reflect reality. Our nanomesh sensor frees researchers to study cardiomyocytes and other cell cultures in a way more faithful to nature. The key is to use the sensor in conjunction with a flexible substrate for the cells to grow on.’

Spinning around

Making the sensors involves electro-spinning to extrude ultrafine polyurethane strands into a flat sheet, which is then coated in the polymer parylene for strength. Stencil dry etching removes the parylene on certain sections of the mesh and gold is applied to these areas to make the sensor probes and communication wires. Additional polymer isolates the probes so their signals do not interfere with one another.

The base for the culture was a very soft fibrin gel -- a material commonly used in biomedical applications. The nanomesh sensor was placed on top of the cell culture in a delicate process to correctly orient the sensor.

Lee found the process frustrating, commenting, ‘The polyurethane strands, which underlie the entire mesh sensor, are 10 times thinner than a human hair. It took a lot of practice and pushed my patience to its limit, but I eventually made some working prototypes.’

With three probes, the sensor reads voltage present at three locations. The readout is essentially a cardiogram allowing the researchers to see propagation of signals, resulting from, and triggering the cells to, beat. These signals are known as an action or field potential and are extremely important when assessing the effect of pharmaceuticals on the heart.

The porous nature of the nanomesh sensor enhances it’s functionality for studying the efficacy of new drugs. The combination of ultrasoft electronics with nanomeshes that allow cells to move dynamically without interference could aid in the study of other cells, organs and medicines. It also paves the way for future embedded medical devices.

The paper Ultra-soft electronics to monitor dynamically pulsing cardiomyocytes appears in Nature Nanotechnology: