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Synthetic Biology

Synthetic nerve transmits signals

Nerve made of hydrogel and aqueous droplets responds to light

by Celia Henry Arnaud
April 28, 2022


A hydrogel synthetic nerve with two branches with one droplet at the end and three branches with two droplets at the end.
Credit: Adapted from Nat. Chem.
Light-activated sensory droplets (left) generate an ionic current that flows through a hydrogel axon to three sets of paired droplets (right). The ions trigger the release of a neurotransmitter from presynaptic to postsynaptic droplets.

Researchers have created synthetic nerves that convey signals over centimeter-scale distances in response to light. The long-term goal is to make tissue-like materials that can communicate with biological systems.

Charlotte E. G. Hoskin, Hagan Bayley, and coworkers at the University of Oxford made the synthetic nerves from a hydrogel with aqueous droplets at both ends (Nat. Chem. 2022, DOI: 10.1038/s41557-022-00916-1). At one end, a sensory droplet contains an archaebacterial membrane protein that pumps protons into the hydrogel in response to light. At the other end are two droplets that play the role of the synapse, the interface between two neurons where communications are exchanged. The first droplet contains the neurotransmitter ATP and pore-forming proteins. When an ionic current travels down the synthetic hydrogel axon, it causes a pH change in the first droplet, causing it to release ATP into the second. In turn, the ATP activates a fluorescent dye, allowing the researchers to detect transmission of the electrical signal from the “presynaptic” droplet to the “postsynaptic” droplet.

The researchers used a pH-sensitive dye to observe the changes, but this readout is much slower than the actual signal transmission within the synthetic nerve, which Bayley suspects happens on a microsecond time scale. “You have to keep the proton pump going for a long time before you can see a pH change using a dye,” Bayley says. “But the electrical signal itself is propagated very rapidly.”

Two-way communication could be possible if the team placed proton pumps at either end of the artificial neuron, Bayley says. “Depending on where you shine the light, the signal could move in either direction.”

The researchers were able to collect multiple synthetic axons into a bundle by embedding them in an elastomeric material. A different signal can be sent down each of the axons in the bundle simultaneously with no cross talk, Bayley says. He envisions eventually using such systems as drug delivery devices or as cardiac patches to treat arrhythmia. These sorts of devices could be controlled externally with light, eliminating the need for bulky onboard electronics and batteries.

“Although the system developed in this work is far from being implementable for medical use, it elegantly integrates noninvasive induction and electrochemical signals into soft materials,” says Aurore Dupin, a researcher at the Weizmann Institute of Science who has worked on synthetic biological systems. “This study presents an important step in the effort of the field of synthetic biology to combine artificial cells and biomaterials to create more relevant and applicable systems.”



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