bacteria Geobacter sulfurreducens Came from humble beginnings; it was first separated from the dirt in a ditch Norman, OklahomaBut now, surprisingly remarkable microorganisms hold the key to the first artificial neurons that can interact directly with living cells.
Yes. sulfurreducens They communicate with each other through tiny, protein-based wires that researchers at the University of Massachusetts Amherst have assembled and used to create artificial neurons that, for the first time, can process information from living cells without any intermediary devices that amplify or modify the signals, researchers say.
While some artificial neurons already exist, they require electronic amplification to understand the signals produced by our bodies, explains jun yaoWho works on bioelectronics and nanoelectronics at UMass Amherst. Amplification increases both power usage and circuit complexity, and therefore counteracts the capabilities found in the brain.
Yao’s team’s neuron can sense the body’s signals at a natural amplitude of about 0.1 volt. It’s “highly innovative,” says bozhi tianA biophysicist who studies living bioelectronics lives at the University of Chicago and was not involved in this work. The work “bridges the long-standing gap between electronic and biological signaling” and demonstrates interactions between artificial neurons and living cells that Tian calls “unprecedented.”
Real neurons and artificial neurons
Biological neurons are the basic building blocks of the brain. If external stimuli are strong enough, a charge builds up in the neuron, triggering an action potential, a spike of voltage that travels through the body of the neuron, enabling all kinds of physiological functions, including emotion and movement.
Scientists have been working for decades to engineer a synthetic neuron, chasing the efficiency of the human brain, which until now appears to have eluded the capabilities of electronics.
Yao’s group has designed 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 increases from external biochemical events, ions accumulate and begin to form a filament across a gap in the memristor – which in this case was filled with protein nanowires. If there is enough voltage, the filament bridges the gap completely. Current flows through the device, and then the filament dissolves, the ions scatter and the current stops. The entire process mimics the action potential of a neuron.
The team tested their artificial neurons by attaching them to heart tissue. The devices measured a baseline amount of cellular contraction, which did not generate enough signal to fire in the artificial neuron. The researchers then took another measurement after giving the tissue a dose of norepinephrine – a drug that increases the frequency of cells’ contractions. The artificial neurons triggered action potentials only during high, pharmacological testing, proving they could detect changes in living cells.
The experimental results were published on 29 September nature communication,
natural nanowire
the group has Yes. sulfurreducens Give thanks for success.
Microbes synthesize miniature cables, called protein nanowires, which they use for interspecies communication. These cables are charged conductors that survive for a long time in the wild without decaying. (Remember, they were developed for the Oklahoma trenches.) They’re extremely stable, even for equipment manufacturing, Yao says.
For engineers, the most remarkable property of nanowires is how efficiently ions move along them. Nanowires offered a low-energy means of transferring charge between human cells and artificial neurons, thus avoiding the need for a separate amplifier or modulator. “And surprisingly, the material is designed for it,” says Yao.
The group developed a method of cutting cables from the bacteria’s body, purifying the material, and suspending it in a solution. They laid out the mixture and allowed the water to evaporate, leaving behind a molecule-thin film made of the protein nanowire material.
This efficiency allows the artificial neuron to generate huge power savings. Yao’s group integrated the film into the memristor at the core of the neuron, thereby lowering the energy barrier for the reaction that causes the memristor to respond to signals detected by the sensor. Researchers say that with this innovation, the artificial neuron uses 1/10th the voltage and 1/100th the power.
Chicago’s Tian believes this “extremely impressive” energy efficiency “is needed for future low-power, implantable and biointegrated computing systems.”
The researchers say the electrical advantages make this synthetic neuron design attractive for all kinds of applications.
Tian says that responsive wearable electronics, such as prosthetics that adapt to stimuli from the body, could use these new artificial neurons. Ultimately, implantable systems that rely on neurons “could learn like living tissues, advancing personalized medicine and brain-inspired computing” to “interpret physiological conditions, leading to biohybrid networks that blend electronics with living intelligence,” he says.
Artificial neurons may also be useful in electronics outside the biomedical field. Yao says millions of them on a chip could replace transistors, accomplishing the same tasks while reducing power use. He says the process for manufacturing neurons does not involve high temperatures and silicon chip makers use the same type of photolithography.
However, Yao points to two potential hurdles that producers may face when scaling up these artificial neurons for electronics. The first is to get more protein from nanowires. Yes. sulfurreducensHis laboratory currently works for three days to generate just 100 micrograms of material – which is equivalent to the mass of a grain of table salt. And that amount can only cover a very small device, so Yao questions how this step in the process could scale up to production.
Their second concern is how to get a uniform coating of the film at the scale of a silicon wafer. “If you want to make high-density, miniaturized devices, film thickness uniformity is a really important parameter,” he explains. But the artificial neurons his group has developed are currently too small for any meaningful uniformity testing.
Tian doesn’t expect artificial neurons to replace silicon transistors in traditional computing, but rather sees them as “a parallel offering to hybrid chips that combine biological adaptability with electronic precision,” he says.
In the distant future, Yao hopes that such bio-derived devices will also be appreciated for not contributing to e-waste. When a user no longer wants the device, they can dump the biological component into the surrounding environment, Yao says, as it won’t pose an environmental threat.
“By using nature-derived, microbial materials like this, we can create a greener technology that is more sustainable for the world,” Yao says.
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