Fungi could become the memory of future computers

An electrical memory component called a “memristor” (memory + resistor) is attracting attention towards next-generation computers. While this technology has the excellent property of storing electrical states, its production requires rare minerals and large-scale semiconductor factories. In recent years, bioprocessors called “brain organoids”, which use cultured brain cells, have gained popularity; however, they require maintenance and complex management in bioreactors. Now, a US research team has shown that fungal mycelium can function as a memristor. The mycelium is a set of fungi with a filamentous and root-like structure that grows on dead wood and other surfaces under certain conditions. In recent times, its potential as a new source of materials, including biodegradable functional biopolymeric fibers, has been actively investigated. “If we could develop a microchip that mimics real neuronal activity, we could drastically reduce the amount of energy consumed when the machine is not in use,” explains the study director, John LaRocco, from the Ohio State University College of Medicine. “This could have significant technological and economic advantages.”

Ecological and Low Cost

LaRocco and his team cultivated shiitake mycelium and other fungi on standard Petri dishes and stored it by drying it in the sun once it reached its full development. This process transforms the mycelium into rigid disc-shaped structures. When they are to be used, they can be rehydrated by spraying them with water to restore their electrical properties. The researchers connected electrodes to the prepared samples and measured the response when passing currents of different voltages and frequencies. Since the different parts of the mycelium have different electrical properties, they looked for the optimal conditions by varying the connection points.

After approximately two months of experiments, it was discovered that the shiitake-based memristor was capable of changing its electrical state up to 5,850 times per second with an accuracy close to 90%. In particular, by applying a 10 Hz sine wave at 1 V, a figure-eight curve (known as a ‘narrow hysteresis loop’) appeared, characteristic of an ideal memristor. This clearly demonstrates that the mycelium remembers the electrical flow. Researchers claim that, while performance decreased at higher frequencies, connecting multiple samples restored stability, a phenomenon that, according to them, closely resembles the network effect of neural connections in the human brain. The main advantage of mycelium-based memristors is their sustainability. Conventional semiconductors require rare transition metal oxides or silicon-based structures for their manufacture, and their disposal poses a significant environmental burden. In contrast, fungi are obtained from organic biomass and are biodegradable, meaning they have a minimal environmental impact. Furthermore, their cultivation is economical and their production is easily scalable, allowing for flexible adaptation from small-scale experiments in Petri dishes to mass production on an industrial scale.

Scalable Use in Many Fields

The most notable thing is that this memristor could be highly resistant to radiation. Conventional semiconductors always run the risk of malfunctions due to space radiation. Components derived from fungi not only offer physical flexibility and energy efficiency, but also have the potential to continue functioning normally in hostile environments, such as space. In the future, the flexibility and scalability of fungi are expected to be harnessed in a wide range of fields, from macro-scale applications such as edge computing and space exploration to micro-scale applications such as autonomous systems and wearable devices. This could lead to the creation of computing substrates with the adaptability and self-repairing capabilities of living organisms, which are not found in conventional electronic components. However, there are still several challenges to overcome before it can be put to practical use. The current sample is relatively large and further miniaturization is required to compete with existing conventional microchips. In addition, since the electrical properties of individual mycelia vary even when grown in the same medium, establishing a stable manufacturing process is an urgent task. The research team plans to develop a technique to cultivate mycelium with ideal shapes using a 3D printer and a method to incorporate electrical contacts during cultivation. They are also exploring the optimal way to preserve it in the long term, combining various techniques such as freeze-drying and special coatings. This is how shiitake mushrooms, a common food ingredient, shed light on the contradictory challenges of solving the e-waste problem and developing next-generation information technology.