Scientists invent ultra-thin, minimally invasive, light-controlled pacemaker

Sometimes our bodies need a boost. Millions of Americans rely on pacemakers, small devices that regulate the heart’s electrical impulses to keep it beating regularly. But to reduce complications, researchers would like to make these devices even smaller and less intrusive.

A team of researchers at the University of Chicago has developed a wireless, light-powered device that can be implanted to regulate the body’s cardiovascular or neural activity. The ultralight membranes, thinner than a human hair, can be inserted through minimally invasive surgery and contain no moving parts.

Published on February 21 in Nature, the results could help reduce complications in cardiac surgery and offer new horizons for future devices.

“The first experiments were very successful and we are really hopeful about the future of this translational technology,” said Pengju Li, a graduate student at the University of Chicago and first author of the paper.

“A new frontier”

Professor Bozhi Tian’s laboratory has for years been developing devices that can use technology similar to solar cells to stimulate the body. Photovoltaic systems are attractive for this purpose because they have no moving parts or wires that can break or become intrusive, which is particularly useful in delicate tissues like the heart. And instead of a battery, researchers simply implant a tiny optical fiber next to it to provide power.

But to get the best results, scientists had to modify the system to work for biological purposes, rather than following the usual solar cell design.

“In a solar cell, you want to collect as much sunlight as possible and move that energy along the cell, regardless of which part of the panel is affected,” Li explained. “But for this application, you want to be able to illuminate a very localized area and activate only that area.”

For example, a common cardiac therapy is known as cardiac resynchronization therapy, in which different parts of the heart are synchronized with precisely programmed loads. In current therapies this is achieved with threads, which can cause their own complications.

Li and the team set out to create a photovoltaic material that would only activate exactly where the light hits.

The final design they settled on features two layers of a silicon material known as P-type, which react to light by creating an electrical charge. The top layer has many small holes, a condition known as nanoporosity, which improve electrical performance and concentrate electricity without allowing it to spread.

The result is a tiny flexible membrane, which can be inserted into the body via a small tube with an optical fiber – a minimally invasive surgery. The optical fiber lights up in a precise pattern, which the membrane captures and transforms into electrical impulses.

The membrane is just a micrometer thick – about 100 times smaller than the finest human hair – and a few centimeters square. It weighs less than a fiftieth of a gram; significantly less than current state-of-the-art pacemakers, which weigh at least five grams. “The lighter a device, the more comfortable it generally is for patients,” Li said.

This particular version of the device is intended for temporary use. Instead of another invasive surgery to remove the pacemaker, it simply dissolves over time in a non-toxic compound called silicic acid. However, the researchers said the devices could be designed to last for different desired lifespans, depending on how long cardiac stimulation is desired.

“This advancement is a game-changer in cardiac resynchronization therapy,” said Narutoshi Hibino, professor of surgery at the University of Chicago Medicine and co-corresponding author of the study. “We are at the dawn of a new frontier where bioelectronics can seamlessly integrate with the body’s natural functions.”

Light use

Although the first trials were carried out on heart tissue, the team said the approach could also be used for neuromodulation, stimulating nerves in movement disorders like Parkinson’s disease, for example, or for treat chronic pain or other disorders. Li coined the term “photoelectroceutical products” to refer to this field.

Tian said the day they first tried the pacemaker in tests with pig hearts, which are very similar to those of humans, sticks in his memory. “I remember that day because it worked on the first try,” he said. “This is both a miraculous accomplishment and a reward for our considerable efforts.”

A screening method developed by Li to map the photoelectrochemical production of various silicon-based materials could also be used elsewhere, Tian pointed out, for example in areas such as new battery technologies, catalysts or photovoltaic cells .