The holes help make sponges and English muffins useful (and, in the latter’s case, delicious). Without holes, they wouldn’t be flexible enough to bend into small crevices or to absorb the perfect amount of jam and butter.
In a new study, scientists from the University of Chicago have found that holes can also improve technology, including medical devices. Posted in natural materials, the article describes a whole new way to make a solar cell: by etching holes in the top layer to make it porous. The innovation could form the basis of a less invasive pacemaker or similar medical devices. It could 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 will open up many possibilities for further improvements in this area.”
Aleksander Prominski, first author of the article
Prominski is a member of the lab of University of Chicago chemist Bozhi Tian, who specializes in creating ways to connect biological tissue and artificial materials; such as wires to modulate brain signals and surfaces for medical implants.
One area 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 operating in the body, these devices are known as photoelectrochemical cells and can be powered from a tiny optical fiber implanted in the body.
Normally, solar cells require two layers, which can be obtained either by combining silicon with another material such as gold, or by mixing different types of atoms in each layer of silicon.
But UChicago scientists from the Tian lab found they could create a solar cell out of pure silicon if they made a layer porous, like a sponge.
The resulting soft, flexible cell can measure less than five microns in diameter, which is about the size of a single red blood cell. It can then be associated with an optical fiber, which can be made as thin as a human hair; dramatically reducing the overall size of an implant, making it more body-friendly and less likely to cause side effects.
The porous cell has multiple advantages over traditional solar cell manufacturing methods, streamlining the production process while maintaining the effectiveness of the end product.
“You can make them in minutes, and the process doesn’t require high temperatures or toxic gases,” Prominski said.
Study co-author Jiuyun Shi added, “When we measured them, we saw that the photocurrent was really high; two orders of magnitude higher than our previous designs.”
Then, to increase the material’s ability to stimulate heart or nerve cells, they treat it with oxygen plasma to oxidize the surface layer. This step is counterintuitive to chemists because silicon oxide most often functions as an insulator, and “you don’t want the photoelectrochemical effect to be hindered by insulating materials,” Tian said. In this case, however, the oxidation actually 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, scientists can imagine the technology used for short-term cardiac procedures. Instead of a second surgery for removal, the parts would naturally degrade after a few months. The innovative approach could also be particularly useful for a procedure called cardiac resynchronization therapy which seeks to correct arrhythmias where the right and left heart chambers do not beat in time, as the devices could be placed in multiple areas of the heart to improve cover. .
Prominski is also excited about possible applications for nerve stimulation. “You can imagine implanting such devices in people with chronic nerve degeneration in the wrists or hands, for example, to relieve pain,” he said.
This new way of making solar cells could also be interesting for sustainable energy or other non-medical applications. Because these solar cells are designed to work best in a liquid environment, UChicago scientists believe they could be used in applications such as artificial leaves and solar fuels.
Tian’s team is working with cardiology researchers at the Medical University of Chicago to further develop the technology for possible use in humans. They are also collaborating 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 utilized the resources of the Pritzker Nanofabrication Facility at the Pritzker School of Molecular Engineering; the Illinois Innovation Network; the Experimental Center for Atomic and Nanoscale Characterization at Northwestern University and the Northwestern Materials Science and Engineering Center; and the University of Chicago Materials Science and Technology Research Center.
Prominsky, A., et al. (2022) Porosity-based heterojunctions enable lead-free optoelectronic modulation of tissues. Natural materials. doi.org/10.1038/s41563-022-01249-7.
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