Conventional neural probes are designed to record a single type of signaling, limiting the information that can be derived from the brain at any point in time. By producing complex multimodal fibers that could be less than the width of a hair, MIT researchers have created a system that could deliver optical signals and drugs directly into the brain, along with simultaneous electrical readout to continuously monitor the effects of the various inputs.

In addition to transmitting different kinds of signals, the new fibers are made of polymers that closely resemble the characteristics of neural tissues, allowing them to stay in the body much longer without harming the delicate tissues around them.

“We’re building neural interfaces that will interact with tissues in a more organic way than devices that have been used previously,” says Polina Anikeeva, an assistant professor of materials science and engineering.

The key to the technology is making a larger-scale version, called a preform, of the desired arrangement of channels within the fiber: optical waveguides to carry light, hollow tubes to carry drugs, and conductive electrodes to carry electrical signals. The polymer templates, which can have dimensions on the scale of inches, are then heated until they become soft, and drawn into a thin fiber, while retaining the exact arrangement of features within them.

A single draw of the fiber reduces the cross-section of the material 200-fold, and the process can be repeated, making the fibers thinner each time and approaching nanometer scale.

Combining the different channels in a single fiber, Anikeeva adds, could enable precision mapping of neural activity, and ultimately treatment of neurological disorders, that would not be possible with single-function neural probes.