Sponge-like solar cells could form the basis for less invasive pacemakers or similar medical devices

Holes help make sponges and English muffins useful (and in the latter case, delicious). Without holes, they wouldn’t be flexible enough to bend into small crevices, or to suck up the perfect amount of jam and butter.

In a new study, scientists at the University of Chicago discover that holes can also improve technology, including medical devices. Published in nature materials, the article describes an entirely new way to make a solar cell: by etching holes in the top layer to make it porous. The innovation could form the basis for a less invasive pacemaker or similar medical devices. It could be combined with a small light source to reduce the size of the bulky batteries currently implanted with current pacemakers.

We hope this offers many opportunities for further improvements in this area.”

Aleksander Prominski, first author of the newspaper

Light work

Prominski is a member of the lab of University of Chicago chemist Bozhi Tian, ​​which specializes in creating ways to connect biological tissue and artificial materials; such as wires to modulate brain signals and surfaces for medical implants.

One of the areas they are interested in is making devices that can be powered by light. We know this technology best in the form of solar cells, but they can also use any light source, including artificial ones. When they work in the body, such devices are known as photoelectrochemical cells and can be powered by a small optical fiber implanted in the body.

Normally, solar cells require two layers, which can be achieved by combining the silicon with another material such as gold, or by mixing different types of atoms in each silicon layer.

But scientists at UChicago in the Tian lab found that they could make a solar cell from pure silicon if they made one layer porous, like a sponge.

The resulting soft, flexible cell may be less than five microns in size, which is about the size of a single red blood cell. It can then be combined with an optical fiber, which can be made as thin as a strand of human hair; significantly reduce the overall size of an implant, making it more body-friendly and less likely to cause side effects.

The porous cell has several advantages over the ways of manufacturing traditional solar cells, streamlining the manufacturing process while maintaining the efficacy of the final product.

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

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

To increase the material’s ability to stimulate heart or nerve cells, they then treat it with oxygen plasma to oxidize the surface layer. This step is counterintuitive for chemists, because silicon oxide usually acts as an insulator, and “you don’t want the photoelectrochemical effect to be hindered by insulating materials,” Tian said. In this case, however, oxidation helps by making the silicon material hydrophilic; attracted to water; which amplifies the signal to biological tissues. “Finally, by adding a layer of metal oxide a few atoms thick, you can further improve the properties of the device,” said Pengju Li, another co-author of the study.

Since all components can be made biodegradable, the scientists can envision the technology being used for short-term cardiac procedures. Instead of a second surgery for removal, the parts would deteriorate naturally after a few months. The innovative approach could also be particularly useful for a procedure called cardiac resynchronization therapy, which aims to correct arrhythmias where the right and left chambers of the heart don’t beat in time because the devices can be placed in multiple parts of the heart. to improve coverage.

Prominski is also excited about potential uses for nerve stimulation. “You might imagine such devices being implanted in people with chronic nerve degeneration in the wrists or hands, for example to provide pain relief,” he said.

This new way of making solar cells could also be of interest for renewable energy or other non-medical applications. Because these solar cells are designed to work best in a liquid environment, scientists at UChicago believe they could be used in applications such as artificial foliage and solar fuels.

Tian’s team is working with heart researchers at the University of Chicago Medicine to further develop the technology for eventual use in humans. They are also working with the UChicago Polsky Center for Entrepreneurship and Innovation to commercialize the discovery.

Jiping Yue, Yiliang Lin, Jihun Park and Menahem Rotenberg were also co-authors of the study.

The research leveraged resources from the Pritzker Nanofabrication Facility at the Pritzker School of Molecular Engineering; the Illinois Innovation Network; the Northwestern University Atomic and Nanoscale Characterization Experimental Center and Northwestern Materials Research Science and Engineering Center; and the University of Chicago Materials Research Science and Engineering Center.


Reference magazine:

Prominski, A., et al. (2022) Porosity-based heterojunctions enable lead-free optoelectronic modulation of tissues. Nature materials. doi.org/10.1038/s41563-022-01249-7

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