bizarre, technology

Building Computer Circuits from Slime

It might sound like science fiction, but researchers are actually exploring how to make computer circuits using slime molds. Why slime molds? It turns out that while slime molds don’t have a brain or even a nervous system, they’re able to make chemical-based decisions, and this behavior can be utilized to make some basic circuit components, specifically logic gates.

slime mold physarum polycephalum logic gates
This type of slime mold, the “many-headed slime” (Physarum polycephalum), can be used to make simple logic gates, basic components of computer circuits. (Image credit: Jonatha Gott)

Slime molds are a very unique group, comprising more than 900 species. They superficially look like fungi, and were even previously classified as belonging to this group, but now they belong to their own separate kingdom (and while they’re not fungi, animals, or plants, they’re more closely related to these organisms than they are to bacteria or archaea). The yellow-colored “many-headed slime” (Physarum polycephalum), the slime mold specifically used in recent logic gate studies, thrives in moist, cool areas, such as damp, decaying logs or leaves. In its active phase (called the phasmodium), it grows by sending out tube-like structures, known as pseudopodia, to find food and sense its environment. Overall, because of how P. polycephalum grows and responds to its environment, it’s been called a “self-growing microfluidic system.”

In microfluidic devices, small amounts of water are moved around in a system of small tubes (typically having diameters less than a millimeter). Similarly, the pseudopodia of P. polycephalum contain cytoplasm (a fluid-like gel in living cells) that moves throughout the organism, which can reach meters in length and contain hundreds of connected structures. The individual diameters of the pseudopodia are quite small, about 100 microns (or 0.1 millimeters), which is similar to most lab-made microfluidic devices.

So how can a microfluidic system, like P. polycephalum, be used as a logic gate? Logic gates are basically a simple circuit component that takes in multiple inputs and gives a single output. To make P. polycephalum function like a logic gate, the researchers took advantage of the fact that the slime mold likes to grow its pseudopodia towards food sources (e.g., oatmeal), but is repelled by other chemicals (e.g., table salt). In this way, they could control how the slime mold expands out its many tube-like structures, making a desired shape. They also found that when they give the slimy critters two different dyes to two different pseudopodia, they mix to make a third color. By labeling the original two dyes as “inputs” and the third color an “output,” this slime mold process starts to look like a logic gate. The researchers estimate that about 10-20 gates are in a given 1 x 1 millimeter square of the organism. After these dye experiments, the researchers moved on to using magnetic nanoparticles and fluorescent beads to further investigate how to use these critters as logic gates.

However, the P. polycephalum logic gates are much slower than typical, silicon-based logic gates used in computer circuits — the slime molds take seconds to “compute.” But the slime molds do have the advantage that they can grow and repair themselves.

So while slime mold-powered logic gates aren’t going to be in your computer any time soon, it’s always fascinating to see the offspring of a marriage between two seemingly disparate fields (i.e., electronics and biology).

Check out the resources below for some science fair project ideas that you could do using P. polycephalum!

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