bacteria Geobacter sulfurreducens came from humble beginnings; it was first isolated from the mud in the ditch to Norman, Oklahoma. But now it's amazingly wonderful microbes are the key to creating the first artificial neurons which can interact directly with living cells.
G. serarreducens microbes communicate with each other through tiny protein wires, which researchers from the University Massachusetts Amherst collected and used to make artificial neurons. For the first time, these neurons can process information from living cells without an intermediary device that amplifies or modulates the signals, the researchers say.
Although some artificial neurons already existthey require electronic amplification to sense the signals our bodies produce, explains Jun Yaowho is working on bioelectronics And nanoelectronics at the University of Massachusetts Amherst. Amplification increases both power consumption and circuit complexity, which reduces brain efficiency.
The neuron created by Yao's team can understand body signals at their natural amplitude of about 0.1 volt. This is “highly new,” says God Tiana biophysicist who studies living bioelectronics at the University of Chicago and was not involved in the work. The work “bridges the long-standing gap between electronic and biological signaling” and demonstrates an interaction between artificial neurons and living cells that Tian calls “unprecedented.”
Real neurons and artificial neurons
Biological neurons are the fundamental building blocks of the brain. If external stimuli are strong enough, a charge builds up in the neuron, causing an action potential—a surge of voltage that travels through the neuron's body and activates all types of bodily functions, including emotions and movement.
Scientists have been working on creating a synthetic neuron for decades, chasing efficiency human brainwhich until now seemed to elude the possibilities of electronics.
Yao's group has developed new artificial neurons that mimic the way biological neurons sense and respond to electrical signals. They use sensors to monitor external biochemical changes and memristors-essentially resistors with memory – to simulate the action potential process.
As the voltage of external biochemical events increases, the ions accumulate and begin to form a filament through a gap in the memristor, which in this case was filled with protein. nanowires. If the voltage is sufficient, the filament completely bridges the gap. A current passes through the device and then the filament dissolves, dispersing the ions and stopping the current. The entire process mimics the action potential of a neuron.
The team tested their artificial neurons by connecting them to heart tissue. The devices measured a baseline amount of cell contraction that did not provide enough signal to trigger the artificial neuron. The researchers then took another measurement after injecting the tissue with norepinephrine, a drug that increases the frequency of cell contraction. The artificial neurons fired action potentials only during the drug study, proving they could detect changes in living cells.
The results of the experiment were published on September 29 in the journal Natural communications.
Natural nanowires
The group has G. serarreducens thank you for the breakthrough.
Microbes synthesize miniature cables called protein nanowireswhich they use for intraspecific communication. These cables are charge conductors that last for long periods of time in the wild without degrading. (Remember, they evolved for Oklahoma ditches.) They're extremely stable, even for making devices, Yao says.
For engineers, the most remarkable property of nanowires is how efficiently ions move through them. Nanowires offer a low-energy means of transferring charge between human cells and artificial neurons, avoiding the need for a separate amplifier or modulator. “And what’s amazing is that the material is designed to do just that,” says Yao.
The team developed a method for separating the cables from the bacterial bodies, purifying the material and suspending it in a solution. The team spread the mixture and let the water evaporate, leaving a one-molecule-thick film of protein. nanowire material.
This efficiency allows the artificial neuron to provide enormous energy savings. Yao Group integrated the film into memristor in the neuron nucleus, lowering the energy barrier to the reaction that causes the memristor to respond to signals recognized by the sensor. According to the researchers, thanks to this innovation, the artificial neuron uses one-tenth less voltage and 1/100th the power of others.
Tian from Chicago finds it “extremely impressive” energy efficiency is “necessary for the future low-powerimplantable and biointegrated computer systems.”
The energetic advantages make this synthetic neuron design attractive for all kinds of applications, the researchers say.
Responsive wearable electronics such as prosthetics Those that adapt to the body's stimuli could use these new artificial neurons, Tian said. Eventually, implantable neuron-based systems will be able to “learn like living tissue, developing personalized medicine and brain-based computing technologies” to “interpret physiological states, leading to biohybrid networks that combine electronics with living intelligence,” he says.
Artificial neurons may also be useful in electronics outside the biomedical field. Millions of them on a chip could replace transistorsperforming the same tasks while reducing energy consumption,” says Yao. The neuron manufacturing process does not require high temperatures and uses the same type photolithography so do silicon chip makers, he says.
However, Yao points to two possible bottlenecks that manufacturers may face when scaling the use of artificial neurons for electronics. The first is to obtain more protein nanowires from G. serarreducens. His lab is currently working for three days to obtain just 100 micrograms of material—about the weight of one grain of table salt. And that amount can only cover a very small device, so Yao wonders how this step in the process can be scaled up for production.
His other concern is how to achieve uniform film coverage at scale silicon wafer. “If you want to make small, high-density devices, film thickness uniformity is actually a critical parameter,” he explains. But the artificial neurons his team has developed are too small to allow any meaningful homogeneity testing at this time.
Tian doesn't expect artificial neurons to replace silicon transistors in conventional computing, but instead sees them as a parallel offering of “hybrid chips that combine biological adaptability with electronic precision,” he says.
In the distant future, Yao hopes that such bioderivative devices will also be appreciated for not contributing to electronic waste. According to Yao, when a user no longer needs the device, they can simply throw the biological component into the environment as it will not pose an environmental hazard.
“By using such natural microbial material, we can create a greener technology that is more sustainable for the world,” says Yao.
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