Implanted at the surface of the brain, the LED-lit microneedles can deliver light to 181 different sites (1.5mm deep), each providing sufficient light to optogenetically excite hundreds of neurons in vivo, according to the researchers.
Described in the Neurophotonics journal in a paper titled “Multisite microLED optrode array for neural interfacing”, the 4×4mm array can be used to independently illuminate specific brain regions while also providing relatively wide-area brain surface illumination if required.
This is to be used in so-called optogenetics performed on larger mammals than laboratory mice, where scientists want to be able to selectively activate or deactivate neurons by illuminating them with light. The stack also includes a pinhole mask to ensure that light can only be emitted from the needles and the surface LEDs.
The paper also gives details about the array’s thermal behaviour and how to prevent excessive heat dissipation from the LEDs. Through thermal simulations, they found that limiting the LEDs operation to a one to two percent duty cycle would prevent heating brain tissue above 1°C while delivering peak irradiances over 80 mW/mm2 per needle at 50 ms pulse widths.
They expect this limitation could be improved by replacing the glass substrate with a thinner silicon substrate with better coupling.
What’s more, the entire array can be battery powered and implanted using standard techniques, and the LED drivers on the implant could be controlled wirelessly, allowing full mobility for the mammal under investigation.
University of Strathclyde – www.strath.ac.uk