Solar Powered Medical Devices: Sponge-Like Solar Cells for Better Pacemakers

A new type of solar cell developed by researchers at the University of Chicago might help advance technology.

As solar technology improves, resulting in higher efficiency and cheaper costs, an increasing number of Americans are turning to it for household electricity. According to the Solar Energy Industries Association (SEIA), solar power capacity in the United States is expected to be 97.2 gigawatts (GW). To give you an idea of how much this is, it's around the same amount of energy as 18 million ordinary houses and accounts for almost 3% of all electricity in the United States.

What about applications on a smaller scale? Solar power might offer significant advantages there that are unrelated to the environmental benefits of large-scale solar.

Sponge and English muffins benefit from holes (and, in the case of the latter, delicious). They wouldn't be flexible enough to bend into little spaces or soak up the appropriate amount of jam and butter if they didn't have holes.

According to a new research from the University of Chicago, holes can enhance technology, particularly medical equipment. The work, which was published in Nature Materials, reveals a brand-new method for making solar cells: etching holes in the top layer to make it porous.

The breakthrough might lead to a less intrusive pacemaker or other medical devices. It might be used in conjunction with a modest light source to minimize the size of the large batteries that come with today's pacemakers.

“We hope this opens many possibilities for further improvements in this field,”  said Aleksander Prominski, the paper's first author.

Light work

Prominski works at chemist Bozhi Tian's lab at the University of Chicago, where he develops techniques to combine biological tissue with artificial materials, such as wires for modulating brain impulses and surfaces for medical implants.

Making gadgets that can be powered by light is one of the areas they're interested in. Solar cells are the most common type of this technology, although it may also be used with any light source, including artificial light. Photoelectrochemical cells are devices that operate in the body and are driven by a small optical fiber implanted in the body.

Solar cells typically have two layers, which are created by combining silicon with another material, such as gold, or by mixing various types of atoms into each silicon layer.

However, researchers at the Tian lab at UChicago discovered that making one layer porous, like a sponge, allowed them to make a solar cell out of pure silicon.

The resultant soft, flexible cell is around the size of a single red blood cell and can be less than five microns wide. It may then be combined with an optical fiber as thin as a strand of human hair, resulting in a considerable reduction in the total size of an implant, making it more body-friendly and less prone to induce adverse effects.

The porous cell provides a number of advantages over typical solar cell manufacturing methods, including the ability to streamline the manufacturing process while preserving the finished product's performance.

“You can make them in a matter of minutes, and the process doesn’t require high temperatures or toxic gases,” Prominski explained.

“When we measured them, we saw the photocurrent was really high—two orders of magnitude higher than our previous designs,” said research co-author Jiuyun Shi.

They then oxidize the surface layer of the material with oxygen plasma to improve its capacity to activate heart or nerve cells. For chemists, this technique is paradoxical since silicon oxide is often used as an insulator, and  “you don’t want the photoelectrochemical effect to be impeded by any insulating materials,” Tian explained. In this situation, however, oxidization aids the signal to biological tissues by making the silicon material hydrophilic (attracted to water).“Finally, by adding a few-atoms-thick layer of metal oxide, you can further enhance the device properties,” said Pengju Li, another research co-author.

The experts believe the technique might be employed for short-term cardiac operations because all of the components are biodegradable. Instead of requiring a second operation to remove the pieces, they would decay naturally over time. Because the devices could be placed in multiple areas of the heart to improve coverage, the innovative approach could be particularly useful for a procedure called cardiac resynchronization therapy, which aims to correct arrhythmias in which the right and left chambers of the heart do not beat in time.

Prominski is similarly enthusiastic about the potential uses of nerve stimulation.“You could imagine implanting such devices in people who have chronic nerve degeneration in the wrists or hands, for example, in order to provide pain relief,” he explained.

This unique method of producing solar cells might be useful for non-medical uses such as sustainable energy. Because these solar cells perform best in a liquid environment, researchers at UChicago believe they may be employed in applications like fake leaves and solar fuels.

Tian's team is collaborating with University of Chicago Medicine cardiac researchers to further improve the technology for human application. They're also working with the Polsky Center for Entrepreneurship and Innovation at the University of Chicago to commercialize the finding.