As a child, physicist Seth Fraden enjoyed the film “Fantastic Voyage,” about a microscopic submarine traveling through a human bloodstream. About a decade ago, Fraden started a quest to build a robotic eel he could launch on a similar journey, though it would not be for the purpose of entertainment. The eel would be engineered to deliver a drug to genes or cells. Furthermore, to capture the flexibility of the real sea creature, it would be in the form of a gel that could slither through water.
This spring, Fraden stated he had accomplished the first couple of steps toward reaching his vision. In the journal Lab on a Chip, he explained he and his team had developed a model using chemicals and microscopic containers of a network of neurons. It’s this network that is principally responsible for the eel’s characteristic zigzag swimming motion.
Subsequently, Fraden plans to implant his neural network in a gel. If everything goes as scheduled, the gel will essentially move in the same manner as an eel does while swimming.
Why an eel?
The robotic eel is part of a larger research by Fraden to construct machines made from chemicals and other synthetic materials that act like living organisms. “Animating inanimate matter” is how he explains it. He’s not converting inorganic matter to life. He’s constructing devices that behave like features and aspects of living creatures — clothing that repairs itself using the same process human cells use to close a wound, for instance, or nanobots that swim like fish via water pipes, transporting materials to repair pipe damage. Fraden’s artificial neural network is simply the beginning.
Compared to many sea creatures, the eel has a comparatively simple system for swimming. Its spine can be found along the length of its body and is surrounded on either side by a column of neurons. When neurons fire successively down one of the columns, they create a wave of muscular contraction, making the spine curve. When the neurons in the other column fire, they make the spine curve in the opposite direction. The result is an effortless smooth back-and-forth motion of the spine as the eel swims.
Fraden is using a three-step process to construct his drug-delivery eel.
Step 1: Create a neuron.
Neurons vacillate between two states — inhibitory and excitatory. In the excitatory state, they cause other neurons to fire and when they are in the inhibitory state, they keep other neurons from firing.
There is a group of chemical reactions that vacillates between two states, comparable to those of a neuron. First detected in the 1950s and 60s by the Russian scientists Boris Belousov and Anatol Zhabotinsky, the ‘BZ reaction’, goes to and fro between states of activity and inactivity.
Irv Epstein, the Henry F. Fischbach Professor of Chemistry, is one of the world’s leading experts in the BZ reaction. He worked along with Zhabotinsky, who came to Brandeis as an adjunct professor of chemistry after the fall of the Soviet Union. It was Epstein, together with several other researchers, who highlighted that the active/inactive pattern of the BZ reaction was corresponding to the exhibitory/inhibitory behavior of nerve cells. This led Fraden to adopt BZ reactions to develop his artificial neurons.
With his newly discovered “neurons” ready, Fraden and his lab engineered a container to hold them. It resembled an ice cube tray with two columns, each divided into separate ice cube compartments.
Step 2: Build a neural network.
As Fraden intended it, every ice cube compartment was a separate neuron. This made the columns comparable to the lines of neurons found on both sides of the eel’s backbone.
Fraden filled each of the ice cube chambers with a liquid solution having the chemicals needed for the BZ reaction. The first BZ reaction occurred in the container at the top of one of the columns. When it turned active (excitatory), it let out a molecule that entered the ice cube container directly under it, triggering the.
Subsequently, the BZ reaction turned inactive (inhibitory). It then let out a molecule that traveled to the ice cube container directly across from it, effectively overpowering, or putting on hold, the BZ reaction in that container.
A pattern materialized. One by one, the BZ reactions in a column were triggered, while the BZ reactions in the other column were placed on a pause mode. When all the BZ reactions in the first column were finished, the reactions in the second column came out of the pause mode and began reacting.
The second column’s reactions also took place one after the other, downward. Plus they also currently inhibited the reactions in the first column. Therefore, the first column began again only after the second column’s reactions were completed.
Extraordinarily, the BZ reactions were interlinked and communicated with each other in the same order as the eel’s spinal neurons, turning off one at a time, one column after the other. Fraden interweaved the BZ reactions together so that they, in operation, acted together as one entity.
The reason behind why the activating molecules moved only vertically and the deactivating ones only horizontally was because of the design of the dividers between the containers. Dividers in the columns permitted only activating molecules to go through. Dividers between the columns allowed only deactivating ones.
The third step: The neural network goes into a gel.
Fraden has chosen a chemical-responsive shape-changing gel into which he will embed his ice cube tray apparatus. “We hope the material will behave in the same way an eel’s body does in response to the firings of its neurons,” he says. “It will slither away.”
Fraden's study received financial assistance from the U.S. Army Research Laboratory and The National Science Foundation (NSF).