Most individuals wouldn’t give Geobacter sulfurreducens a re-evaluation. The bacteria was first discovered in a ditch in rural Oklahoma. However the lowly microbe has a superpower. It grows protein nanotubes that transmit electrical signals and uses them to speak.
These bacterial wires are actually the idea of a brand new artificial neuron that prompts, learns, and responds to chemical signals like an actual neuron.
Scientists have long desired to mimic the brain’s computational efficiency. But despite years of engineering, artificial neurons still operate at much higher voltages than natural ones. Their frustratingly noisy signals require an additional step to spice up fidelity, undercutting energy savings.
Because they don’t match biological neurons—imagine plugging a 110-volt device right into a 220-volt wall socket—it’s difficult to integrate the devices with natural tissues.
But now a team on the University of Massachusetts Amherst has used bacterial protein nanowires to form conductive cables that capture the behaviors of biological neurons. When combined with an electrical module called a memristor—a resistor that “remembers” its past—the resulting artificial neuron operated at a voltage much like its natural counterpart.
“Previous versions of artificial neurons used 10 times more voltage—and 100 times more power—than the one we now have created,” said study writer Jun Yao in a press release. “Ours register only 0.1 volts, which [is] concerning the same because the neurons in our bodies.”
The unreal neurons easily controlled the rhythm of living heart muscle cells in a dish. And adding an adrenaline-like molecule triggered the devices to up the muscle cells’ “heart rate.”
This level of integration between artificial neurons and biological tissue is “unprecedented,” Bozhi Tian on the University of Chicago, who was not involved within the work, told IEEE Spectrum.
Higher Option to Compute
The human brain is a computational wonder. It processes an unlimited amount of knowledge at very low power. Scientists have long wondered the way it’s able to such feats.
Massively parallel computing—with multiple neural networks humming along in sync—could also be one factor. More efficient hardware design could also be one other. Computers have separate processing and memory modules that require time and energy to shuttle data forwards and backwards. A neuron is each memory chip and processor in a single package. Recent studies have also uncovered previously unknown ways brain cells compute.
It’s no wonder researchers have long tried to mimic neural quirks. Some have used biocompatible organic materials that act like synapses. Others have incorporated light or quantum computing principles to drive toward brain-like computation.
In comparison with traditional chips, these artificial neurons slashed energy use when faced with relatively easy tasks. Some even connected with biological neurons. In a cross-continental test, one artificial neuron controlled a living, biological neuron that then passed the commands on to a second artificial neuron.
But constructing mechanical neurons isn’t for the “whoa” factor. These devices could make implants more compatible with the brain and other tissues. They may additionally give rise to a more powerful, lower energy computing system in comparison with the establishment—an urgent need as energy-hogging AI models attract tons of of thousands and thousands of users.
The Lifetime of a Neuron
Previous artificial neurons loosely mimicked the way in which biological neurons behave. The brand new study sought to recapitulate their electrical signaling.
Neurons aren’t like light switches. A small input, for instance, isn’t enough to activate them. But as signals consistently construct up, they trigger a voltage change, and the neuron fires. The electrical signal travels along its output branch and guides neighboring neurons to activate too. Within the blink of a watch, the cells connect as a network, encoding memories, emotions, movement, and decisions.
Once activated, neurons go right into a resting mode, during which they’ll’t be activated again—a temporary reprieve before they tackle the subsequent wave of electrical signals.
These dynamics are hard to mimic. However the tiny protein cables G. sulfurreducens bacteria use to speak may help. The cables can withstand extremely unpredictable conditions, reminiscent of Oklahoma winters. They’re also particularly adept at conducting ions—the charged particles involved in neural activity—with high efficiency, nixing the necessity to amplify signals.
Harvesting the nanocables was a bit like drying wild mushrooms. The team snipped them off collections of bacteria and developed a strategy to rid them of contaminants. They suspended the wispy proteins in liquid and poured the concoction onto an excellent surface for drying. After the water evaporated, they were left with a particularly thin film containing protein nanocables that retained their electrical capabilities.
The team integrated this film right into a memristor. Like in neurons, changing voltages altered the substitute neuron’s behavior. Built-up voltage caused the protein nanowires to bridge a niche contained in the memristor. With sufficient input voltage, the nanocables accomplished the circuit and electrical signals flowed—essentially activating the neuron. Once the voltage dropped, the nanocables dissolved, and the substitute neurons reset to a resting state like their biological counterparts.
Since the protein wires are extremely sensitive to voltage changes, they’ll instruct the substitute neurons to change their behavior at a much lower energy. This slashes total energy costs to 1 percent of previous artificial neurons. The devices operate at a voltage much like biological neurons, suggesting they may higher integrate with the brain.
Beating Heart
As proof of concept, the team connected their invention to heart muscle cells. These cells require specific electrical signals to maintain their rhythm. Like biological neurons, the substitute neurons monitored the strength of heart cell contractions. Adding norepinephrine, a drug that rapidly increases heart rate, activated the substitute neurons in a way that mimics natural ones, suggesting they may capture chemical signals from the environment.
Even though it’s still early, the substitute neurons pave the way in which for uses that seamlessly bridge biology and electronics. Wearable devices and brain implants inspired by the devices could yield prosthetics that higher “talk” to the brain.
Outside of biotech, artificial neurons might be a greener alternative to silicon-based chips if the technology scales up. Unlike older designs that require difficult manufacturing processes, reminiscent of extreme temperatures, this recent iteration could be printed with the identical technology used to fabricate run-of-the-mill silicon chips.
It won’t be a simple journey. Harvesting and processing protein nanotubes stays time consuming. It’s yet unclear how long the substitute neurons can remain fully functional. And as with every device including biological components, more quality control can be needed to make sure even manufacturing.
Regardless, the team is hopeful the design can encourage simpler bioelectronic interfaces. “The work suggests a promising direction toward developing bioemulated electronics, which in turn can result in closer interface with biosystems,” they wrote. Not too bad for bacteria discovered in a ditch.