The Plastic Brain

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When I was a kid I devised to biomechanical car, that used muscles instead of pistons in the drive train, and ran on grass instead of petrol – like a horse, you know.

Glad to see that someone is moving to make my dream a reality.

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I started my tertiary education as a Chemical Engineer. I learned about how complex systems could be managed by a top-down approach. A central processor could monitor and regulate, for instance, the flow rate in numerous pipes within a refinery. Incidentaly, I was consequently also made aware of the Hagen-Poiseuille equation for laminar flow in a pipe. A subject which put a strain on even my interest in formulae.

Due to a stroke of fortune, I ended up with free units in first year, and was able to take up an elective subject. On a whim I chose an introductory biology course. I had never done biology at school. It wasn’t considered a serious subject by us hardened maths/physics/chem types. Besides which, I was limited to only two science subjects.

To cut a long story short, I found myself loving biology, and turning my back on engineering. And the simple reason was this: Bottom-up, distributed, self-organisation. Biology is full of it, but engineering struggles. A plant is simalr to a refinery in that is regulates flow in a lots of pipes – but it does so without a central processes. To take one example:

For a leaf to operate, it needs air to circulate to the interior of the leaf, via pores called stomata. This allows carbon dioxide in, oxygen out. Water also escapes by a process called transpiration. This is a problem. Leaving pores open all the time will lead to excessive water loss. The solution? Use the water content itself to open and close the pores. More water=pores open. Water scarce=pores close. It is, in truth, a fairly complicated process, but what it boils down to is that when water is abundant, it enters the two guard cells which flank to pore, they enlarge and are forced outward, opening the pore. In conditions of low water, the cells ‘deflate”, and come together, closing the pore, as reducing further water vapour loss.

Guard cells of a stomate

I have often marvelled at how pairs of cells, distributed over the surface of a leaf, can so exquisitely work in concert to regulate water levels, both at the local (their leaf) and global (whole plant) level. Wouldn’t it be nice if engineering could do the same?

Well, that’s where biomimicry comes in. Myriad examples can be found by searching the web. But I present here my own, humble contribution the the field. Can we make a synthetic plantoid that can sense water levels in soil, and regulate a watering system that will only water our plants when they are thirsty? Can it be built without any sensors or electronics? I think so. The example presented below really relies on that other plant regulatory tool – wilting. When the device is in moist soil, the “roots” take up water by capillary action, and fill the “stem”, which stands erect and the valve is closed. In dry soil, lack of water in the “stem” causes it to wilt, dropping the weight and opening a dripper system. Hey presto.

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Edit: You know the way I said it was more complicated? Check out this post from Biochemistry, yeah! to delve into the molecular details a little more.