Medical Device Daily National Editor

Putting electrodes in the brain, or other areas of the body, is frequently necessary but offering significant risks – and how much information, or therapy, can they provide, and with what accuracy?

Offering what they believe could be a less-invasive, more flexible method for acquiring and stimulating neural activity is a research duo from Case Western University (Cleveland). The new method, they say, using nanotechnology, has the potential to understand and activate specific regions of the brain and other neural pathways, or potentially restore function to damaged or cut nerves.

Ben Strowbridge, PhD, an associate professor in the neurosciences department at the Case Western Reserve School of Medicine, and Clemens Burda, PhD, associate professor of chemistry, have shown how semiconductor nanoparticles can excite neurons in single cells or groups of cells with visible, near infrared light.

Strowbridge told Medical Device Daily that these particle "dots" essentially could act as tiny solar cells for activating neural data and therapeutic response..

The study, done with rodent brain slices under a microscope and then activated with an infrared light source, is early feasibility work, Strowbridge and Burda acknowledge, saying that it was peripheral to their main activities. And both describe the research result as a rather happy surprise.

Burda, the chemistry expert of the team, told MDD that the next steps will be to embed the nanoparticles in live rodents and, ultimately, in humans.

Another goal, he said, will be to show that the nanoparticles can be placed in both dispersed and targeted ways in order to light up and activate different neural sectors. This, the researchers believe, could be a new way of recreating the complex activity patterns that normally occur in the brain, and, importantly, doing it without wires or traditional electrical power.

Traditional electrical stimulation of the brain, the researchers say, requires an array of metal electrodes to be implanted. But the closer the traditional metal electrode technique gets to re-creating "real" biological activity patterns, the more invasive it becomes. And the more electrodes used, the greater the risk of side effects, from destruction of cells to chemical reaction to the electrode materials.

"There are many different reasons you'd want to stimulate neurons – such as repairing injury or restoring function to severed or damaged nerves. And right now you have to put a wire in there, and then connect that to some control system. It is both very invasive and a difficult thing to do," Strowbridge said.

Burda described the particles chosen for the work as "semiconduction quantum dots," selected because of their ability to absorb long wavelength light, and thus easily irradiated or "stimulated." Human tissue, he added, "is almost transparent in that wavelength range."

The work was launched three years ago, "essentially on the side," Burda said, and turned out to be "more successful than we expected." The result, he said, has been to create "a stimulation device that's incredibly small" and capable of being implanted "anywhere in the body."

The team first combined the nanoparticles with glass to examine toxicity, and then to satisfy the demands of medical use, figured out how to encase the particles in glass for further protection, still managing to keep the particles at micrometer scale. That was done in the lab of Strowbridge, who supplies the biological expertise of the team.

He said the system developed "turned out to be very nice" and could ultimately be used to develop a better understanding of "how brain circuits are organized."

He explained that the actual implementation and applications of the system could be highly varied because of its great flexibility. The nanoparticles might be implanted surgically in the brain or somewhere just under the skin. The light source used to make them light up could range from implanted fiber optics to a handheld laser device, he said.

Applications could range from research on the brain "to create more realistic input patterns," to therapy: "Can you excite the nerves or brain pathways [to treat] spinal chord injury?"

To move the research beyond feasibility – and closer to full-time focus – he said that grants are being sought to hire new staff that can pursue the system's use in animal models.

Strowbridge acknowledged that other methods are being researched as ways to avoid traditional electrodes. These include the exploration of biological systems that are light-sensitive; for instance, there is "a lot of excitement about genetic activation of brain cells."

But he said that this method is more complicated, would require a greater energy source and is more difficult to control.

"Semi-conductor particles" – by contrast – "offer much closer electronic access to the brain and have a very reliable, predictable response. That's not so easy to get with biological methods," he said.

But he said that whichever method proves more useful – and both may be quite serviceable, depending on the particular need, he acknowledged – an important intent will be to find ways to gather a larger, more accurate amount of neural data with less risk to patients than currently provided by standard electrodes.

"The long-term goal of this work," Strowbridge said, "is to develop a light-activated brain interface that restores function following nerve or brain impairments. Our findings may open up a whole new world of research possibilities."

The study was published in the journal Angewandte Chemie (Vol. 48, Issue 13, pp: 2407-2410).