Ultra-thin and flexible probe provides a minimally invasive and durable neural interface

Researchers from the University of California, San Diego and the Salk Institute for Biological Studies have developed a tiny neural probe that can be implanted for longer periods of time to record and stimulate neural activity, while minimizing brain damage. surrounding tissues.

Photograph of a small capsule supporting the neural probe, with a close-up of the microfiber tip. Credit: Spencer Ward

The new neural probe, detailed in an article published on June 7 in Nature Communication, is extremely thin (about one-fifth the width of a human hair) and flexible. The team says this type of neural probe would be ideal for studying small dynamic areas of the nervous system like peripheral nerves or the spinal cord.

“This is where you would need a very small, flexible probe that can fit between vertebrae to interface with neurons and can bend when the spinal cord moves,” said Axel Nimmerjahn, associate professor at the Salk Institute and co-lead author of the study.

These characteristics also make it more compatible with biological tissues and less prone to triggering an immune response, making it suitable for long-term use.

“For chronic neural interfacing, you want a probe that’s stealthy, something the body doesn’t even know is there but can still communicate with neurons,” said the co-lead author. study, Donald Sirbuly, professor of nanoengineering at UC San Diego Jacobs. Engineering school.

Although there are other ultra-thin and flexible probes, what sets this small probe apart is that it can both record the electrical activity of neurons and stimulate specific sets of neurons using light.

“Having this dual modality – electrical recording and optical stimulation – in such a small footprint is a unique combination,” Sirbuly said.

The probe consists of an electrical channel and an optical channel. The electrical channel contains an ultra-thin polymer electrode. The optical channel contains an optical fiber that is also ultra-thin. Putting these two channels together required some clever engineering. Researchers had to figure out how to isolate the channels to keep them from interfering with each other and fit them both into a tiny probe measuring just 8 to 14 micrometers in diameter, while ensuring the device was mechanically flexible, robust, biocompatible and able to perform on par with state-of-the-art neural probes. This involved finding the right combination of materials to construct the probe and optimizing the fabrication of the electrical channel.

The team implanted the probes into the brains of live mice for up to a month. The probes caused virtually no inflammation in brain tissue after prolonged implantation. As the mice moved through a controlled environment, the probes were able to record the electrical activity of neurons with high sensitivity. The probes have also been used to target specific types of neurons to produce certain physical responses. Using the probes’ optical channels, the researchers stimulated neurons in the mice’s cortex to move their whiskers.

These tests in brain tissue were performed as proof of concept. The team hopes to perform future spinal cord studies using their probe.

“Currently, we know relatively little about how the spinal cord works, how it processes information, and how its neural activity might be disrupted or altered in certain pathological conditions,” Nimmerjahn said. “It was a technical challenge to record from this dynamic and tiny structure, and we believe our probes and future probe arrays have the unique potential to help us study the spinal cord, not just understand it at a fundamental level, but also have the possibility of modulating its activity.

UC San Diego and the Salk Institute have filed a patent application on the neural probe technology described in this work.

Article: “Mechanically flexible electro-optic coaxial microprobes for minimally invasive interface with intrinsic neural circuitry.”

This work was supported by the Defense Advanced Research Projects Agency (DARPA) Office of Biological Technologies Electrical Prescription Program (HR0011-16-2-0027), UC San Diego Kavli Institute for Brain and Mind (2018- 1492) and the National Institutes of Health (R01 NS108034, U19 NS112959, U01 NS103522 and P30 CA014195). This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).