This transmission electron microscope image shows the honeycomb structure of the silicon nanowires. Image: Jiang et al.
This transmission electron microscope image shows the honeycomb structure of the silicon nanowires. Image: Jiang et al.

Researchers from the University of Chicago, Northwestern University, the University of Illinois at Chicago and the US Department of Energy's (DOE) Argonne National Laboratory have engineered silicon nanoparticles that when illuminated can make nerve cells fire and heart cells beat. They report this work in a paper in Nature Materials.

Bozhi Tian, who led one of the University of Chicago research groups, said the particles can establish unique biointerfaces on cell membranes, because they are deformable but can still yield a local electrical effect.

"Biological systems are soft, and if you want to design a device that can target those tissues or organs, you should match their mechanical interface as well," Tian said. "Most of the current implants are rigid, and that's one of the reasons they can cause inflammation."

Over time, biointerfaces made out of these silicon particles will also naturally degrade, unlike alternative materials like gold and carbon, explained study co-author Yuanwen Jiang, a graduate student in the Tian group. This means that patients wouldn't have to undergo a second procedure to have the particles removed. Jiang and Tian said they believe the nanomaterial has many potential applications in biomedicine, because the particles can interact with light to excite many types of cells.

The mesostructured silicon, named for its complex internal structure of nanoscopic wires, was created using a process called nano-casting. To make the particles, each 1–5µm in size, the researchers filled the beehive structure of synthetic silicon dioxide with semiconductive silicon, in the same way that a blacksmith would pour molten metal into a cast iron mold. The outer silicon dioxide mold was then etched away with acid, leaving behind a bundle of silicon wires connected by thin bridges.

In order to test whether these particles could change the behavior of cells, the team injected a sample of them onto cultured rat dorsal root ganglia neurons, which are found in the peripheral nervous system. Using pulses of light to heat up the silicon particles, the researchers were able to activate the neurons, causing current to flow through them.

In conventional biointerfaces, materials must be hooked up to a source of energy, but because researchers need only apply light to activate the silicon particles, the new system is entirely wireless. Researchers can simply inject the particles in the right area and activate them through the skin.

"Neuromodulation could take full advantage of this material, including its optical, mechanical and thermal properties," Jiang said.

Along with the implications that controlling neurons might have for neurodegenerative disorders, researchers in Tian's lab have used similar materials to control the beating of heart cells, he said.

To conduct this study, the researchers used resources at the Argonne X-ray Science and Chemical Sciences and Engineering Divisions and at the Center for Nanoscale Materials, a DOE Office of Science User Facility. They used the 12-ID-B and 32-ID beamlines at the Advanced Photon Source, also a DOE Office of Science User Facility, to take X-ray scattering measurements, as well as to conduct transmission X-ray microscopy nano-computed tomography, scanning electron microscopy and transmission electron microscopy. The Center for Nanoscale Materials provided a focused ion beam lithography instrument and expertise, as well as tools for fabricating the optical masks.

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