Feb 18 2019
The emerging technology—neural stimulation—is believed to have beneficial therapeutic effects in Parkinson’s disease and other similar neurological disorders.
A laser shining onto an untethered, ultra-small carbon fiber electrode to stimulate neurons via the photoelectric effect. (Image credit: J. Mater. Chem. B, 2015,3, 4965-4978–Reproduced by permission of The Royal Society of Chemistry.)
Although there have been a number of advancements, the implanted devices are known to induce scarring in neural tissues and deteriorate over a period of time. Takashi D. Y. Kozai from the University of Pittsburgh described a less invasive technique of stimulation that would apply an ultra-small, untethered electrode stimulated by light—a method that may moderate the damage caused by existing techniques. Kozai have detailed the study results in a newly published paper.
Typically with neural stimulation, in order to maintain the connection between mind and machine, there is a transcutaneous cable from the implanted electrode inside of the brain to a controller outside of the body. Movement of the brain or this tether leads to inflammation, scarring, and other negative side effects. We hope to reduce some of the damage by replacing this large cable with long wavelength light and an ultrasmall, untethered electrode.
Takashi D. Y. Kozai, Assistant Professor, Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh
The first author of the paper titled, “Intracortical neural stimulation with untethered, ultra-small carbon fiber electrodes mediated by the photoelectric effect” is Kaylene Stocking, a senior bioengineering and computer engineering student. She works with Kozai’s team—the Bionic Lab—to study how the longevity of neural implant technology can be enhanced by researchers. The study was performed in association with Alberto Vasquez, a research associate professor of radiology and bioengineering at the University of Pittsburgh.
The photoelectric effect is a phenomenon that occurs when a photon, or a particle of light, bombards an object and brings about a local change in the electrical potential. Kozai’s team discovered the benefits of the photoelectric effect while carrying out other imaging studies. Predicated on Einstein’s 1905 publication on this effect, the team believed that electrical photocurrents will be seen only at ultraviolet wavelengths, or high energy photons; however, they experienced an entirely different phenomenon.
“When the photoelectric effect contaminated our electrophysiological recording while imaging with a near-infrared laser (low energy photons), we were a little surprised,” Kozai explained. “It turned out that the original equation had to be modified in order to explain this outcome. We tried numerous strategies to eliminate this photoelectric artifact, but were unsuccessful in each attempt, so we turned the ‘bug’ into a ‘feature.”
Our group decided to use this feature of the photoelectric effect to our advantage in neural stimulation. We used the change in electrical potential with a near-infrared laser to activate an untethered electrode in the brain.
Kaylene Stocking, Study First Author and Senior Student, Department of Bioengineering and Computer Engineering, University of Pittsburgh
The laboratory developed a carbon fiber implant measuring 7-8 µm in diameter, or about the size of a neuron, that is, 17-27 µm. Stocking used a two-photon microscope to replicate this method on a phantom brain. She determined the properties and studied the impacts to see whether the electrical potential caused by the photoelectric effect activated the cells in a way analogous to conventional neural stimulation.
“We discovered that photostimulation is effective,” stated Stocking. “Temperature increases were not significant, which lowers the chance of heat damage, and activated cells were closer to the electrode than in electrical stimulation under similar conditions, which indicates increased spatial precision.”
What we didn’t expect to see was that this photoelectric method of stimulation allows us to stimulate a different and more discrete population of neurons than could be achieved with electrical stimulation. This gives researchers another tool in their toolbox to explore neural circuits in the nervous system. We’ve had numerous critics who did not have faith in the mathematical modifications that were made to Einstein’s original photoelectric equation, but we believed in the approach and even filed a patent application (patent pending:US20170326381A1). This is a testament to Kaylene’s hard work and diligence to take a theory and turn it into a well-controlled validation of the technology.
Takashi D. Y. Kozai, Assistant Professor, Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh
At present, Kozai’s team is exploring other opportunities to further develop this novel technology, including wireless drug delivery and reaching deeper tissue. Stocking expects to graduate in April 2019 and has planned to pursue a doctoral degree.
The University of Pittsburgh has amazing resources that have allowed me to gain meaningful research experience as an undergraduate, and I’m grateful to Dr. Kozai and the Department of Bioengineering for giving me the opportunity to do impactful work.
Kaylene Stocking, Study First Author and Senior Student, Department of Bioengineering and Computer Engineering, University of Pittsburgh