Biology New Fibers Can Deliver Many Simultaneous Stimuli

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The human brain’s complexity makes it extremely challenging to study — not only because of its sheer size, but also because of the variety of signaling methods it uses simultaneously.

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. Now researchers at MIT may have found a way to change that. By producing complex multimodal fibers that could be less than the width of a hair, they 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.

The new technology is described in a paper which appeared in the journal Nature Biotechnology, written by MIT’s Polina Anikeeva and 10 others. An earlier paper by the team described the use of similar technology for use in spinal cord research.

In addition to transmitting different kinds of signals, these fibers are made of polymers that closely resemble the characteristics of neural tissues, Anikeeva says, 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 Anikeeva, an assistant professor of materials science and engineering. To do that, her team made use of novel fiber-fabrication technology pioneered by MIT professor of materials science (and paper co-author) Yoel Fink and his team, for use in photonics and other applications.

Soft and flexible fiber-based neural probes

The result, Anikeeva explains, is the fabrication of polymer fibers “that are soft and flexible and look more like natural nerves.” Devices currently used for neural recording and stimulation, she says, are made of metals, semiconductors, and glass, and can damage nearby tissues during ordinary movement.

“It’s a big problem in neural prosthetics,” Anikeeva says. “They are so stiff, so sharp — when you take a step and the brain moves with respect to the device, you end up scrambling the tissue.”

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.

These 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.

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