A team of researchers led by Northwestern University and the University of Texas at Austin (UT) have developed a novel graphene heart implant that’s about the thickness of a strand of hair and monitors and corrects abnormal heart rhythms using light.

Heart rhythm disorders – cardiac arrhythmias – are caused by faulty electrical signaling in the heart, causing it to beat too quickly or too slowly. In some cases, this can lead to heart failure, stroke, and even sudden death.

Cardiac arrhythmias are commonly treated with implantable pacemakers and defibrillators, which monitor and correct abnormal rhythms. But these devices are inflexible and can constrain the heart, causing tissue injury and discomfort and increasing the risk of complications such as swelling, perforation, blood clots, and infection.

The new pacemaker is the first made from strong, lightweight, biocompatible ‘super material’ graphene and the thinnest to date. Unlike existing implantable pacemakers and defibrillators, this one molds itself to the heart tissue while being strong enough to withstand the rigors of a beating heart.

“One of the challenges for current pacemakers and defibrillators is that they are difficult to affix onto the surface of the heart,” said Igor Efimov, senior author of the study. “Defibrillator electrodes, for example, are essentially coils made of very thick wires. These wires are not flexible, and they break. Rigid interfaces with soft tissues, like the heart, can cause various complications. By contrast, our soft, flexible device is not only unobtrusive but also intimately and seamlessly conforms directly onto the heart to deliver more precise measurements.”

Researchers at UT were already developing a graphene electronic tattoo with sensing capabilities that adheres to the skin to continuously monitor vital signs like blood pressure and electrical activity. For the current study, the researchers used UT’s e-tattoo design to develop a device that could operate inside the body.

They started by encasing the e-tattoo in a flexible silicon membrane, then placed gold tape, approximately 10 microns thick, on it. The gold acts as an electrical connection between the graphene and the electronics used to measure and stimulate the heart. Altogether, the device’s total thickness was about 100 microns. For context, the average human hair is around 70 microns thick.

The researchers tested their device on rats and found that it could accurately sense arrhythmias and then deliver electrical stimulation without constraining the heart’s natural movement. It was stable on an actively beating heart, at body temperature, for 60 days, about the same time temporary pacemakers are used as a bridge to permanent pacemakers.

What’s more, the device’s transparency offers even more advantages, say the researchers, who used light to monitor and control heart rhythm (optocardiography) in their rat subjects. Optical stimulation is a more precise way of correcting arrhythmias than electrical stimulation and, with light, specific enzymes can be tracked and heart, nerve and muscle cells investigated.

“We can essentially combine electrical and optical functions into one biointerface,” Efimov said. “Because graphene is optically transparent, we can actually read through it, which gives us a much higher density of readout.”

The researchers say that using light in this way could provide a new way of diagnosing and treating heart conditions.

The study will be published on 20 April 2023 in the journal Advanced Materials.