A microscope image of a silicon membrane after the hole-etching process. Image: University of Chicago: Physical Sciences Division – Tian Lab.
A microscope image of a silicon membrane after the hole-etching process. Image: University of Chicago: Physical Sciences Division – Tian Lab.

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

In a new study, scientists at the University of Chicago have found that holes can also improve various technologies, including medical devices. In a paper in Nature Materials, the scientists report an entirely new way to make a solar cell: by etching holes in the top layer to make it porous.

This innovation could form the basis for a less-invasive pacemaker or similar medical device. It could also be paired with a small light source to reduce the size of the bulky batteries that are currently implanted with today’s pacemakers.

“We hope this opens many possibilities for further improvements in this field,” said Aleksander Prominski, the first author of the paper. Prominski is a member of the lab of Bozhi Tian, a University of Chicago chemist who specializes in creating ways to connect biological tissue with artificial materials – such as wires to modulate brain signals and surfaces for medical implants.

One of the areas that Tian and his team are interested in is making devices that can be powered by light. Most familiar as the solar cells that generate electricity from sunlight, this technology can actually utilize any light source, including artificial ones. When operating in the body, such devices are known as photoelectrochemical cells and can be powered by a tiny optical fiber implanted in the body.

Normally, solar cells require two layers, which can be produced either by combining silicon with another material such as gold, or by mixing different kinds of atoms into each silicon layer. But scientists in the Tian lab found they could create a solar cell out of pure silicon if they made one layer porous, like a sponge.

The resulting soft, flexible cell can be less than 5µm across, which is about the size of a single red blood cell. It can then be paired with an optical fiber, which can be made as thin as a strand of human hair. This significantly reduces the overall size of the implant, thus making it more body-friendly and less likely to cause side effects.

The porous cell also has multiple advantages over the manufacture of traditional solar cells, streamlining the production 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,” said Prominski.

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

To boost the material’s ability to stimulate heart or nerve cells, the scientists treated it with oxygen plasma to oxidize the surface layer. This step is counterintuitive for chemists because silicon oxide most often works as an insulator, and “you don’t want the photoelectrochemical effect to be impeded by any insulating materials,” said Tian.

In this case, however, oxidization actually helps by making the silicon material hydrophilic – attracted to water – which boosts the signal to biological tissues. “Finally, by adding a few-atoms-thick layer of metal oxide, you can further enhance the device properties,” said Pengju Li, another paper co-author.

Because all of the components can be made to be biodegradable, the scientists imagine this technology being used for short-term cardiac procedures. Instead of a second surgery for removal, the components would degrade naturally after a few months. This innovative approach might be particularly useful for a procedure called cardiac resynchronization therapy, which seeks to correct arrhythmias where the right and left chambers of the heart do not beat in time. The tiny devices could be placed in multiple areas of the heart to improve coverage.

Prominski is also excited about possible applications in 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 said.

This novel way of making solar cells could also be of interest for sustainable energy or other non-medical applications. Because these solar cells are designed to work best in a liquid environment, the scientists think they could be used for applications such as artificial leaves and solar fuels.

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

This story is adapted from material from the University of Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.