The previous post introduced the idea of “desiccation shock” through Martin Grube’s contributed chapter in Advances in Physarum Machines (2016). I made slightly modified plates, with small bands of aluminum conductive tape protruding from the sides of the petri dishes to easily get a hold of them with alligator clips. Here’s a quick run through of what I did, strongly inspired from Andrew Adamatzky’s work on “Physarum wires: Self-growing self-repairing smart wires made from slime mould“:
First I start with my petri dish plates. I measure a section of aluminum conductive tape long enough to get from the center, then comfortably to the edges of the plates, with some extra (the plates I use at the moment are 90 x 15mm, and I cut aluminum strands of about 80mm in length. By the way, I’m not sure how conductive tape width affects conductivity. I’ve read about 8mm wide strips used here, but mine are 6mm wide, yet they seem to conduct current well enough). I use the extra length to fold the tape on itself, so the plate can stay closed when the alligator clips are connected.
The petri dish can be placed on a ruler, just to make sure there’s a close enough standard space of 1cm between the electrodes. Once that is done —or before— I weight 2% of agar flakes or powder and combine in whatever quantity of water needed (say for 100ml of water, I use 2 grams of agar, as indicated in this helpful post). I use a cheap kitchen scale to do this, and bought my agar agar in a health food store. I put that in the microwave on high for about a minute and a half — but keep a careful eye on it: it’ll start foaming and overflowing quickly. I re-heat until the powder or flakes are dissolved.
Once the agar gel is cool enough to handle —after about 5 to 10 minutes of cooling, approximately — I used a small spoon to carefully drop a dollop of it on each tips of the electrodes. I’ve found pouring the gel in a kitchen squeeze tube to be far more practical recently. Once cooled, the unused gel in it can be re-heated in a matter of 20 seconds in the microwave (still on high) for further use.
Once that is done, I put a small oat flake well inoculated with slime mold on one of the agar blobs:
I also add a new oat flake on the other blob. I spray water on the petri dish lid —to keep humidity high enough—, then fold the dish in plastic wrap and secure the wrap with rubber bands.
I fold again in pieces of black garbage bags to make sure the slime mold stays in as dark an environment as possible. I find folding it in cut pieces of garbage bags also makes for easier transport: they fit really neatly in my camera bag.
Keeping the lid on during experimentation has allowed to light up a LED brightly with lower voltage (23.7 volts in this case).
I can see the LED starting to light at about 12 volts —with current set at 0.02 amps. With this setup, an electronics power supply (instead of a laboratory adjustable power supply) could be used.
Things I’m still experimenting with:
- Whether leaving the slime mould to colonize a first blob for about 12 hours — and then adding the new oat flake on the other agar blob — will make the slime mold eager to get to the new oat flake more quickly and directly (
I’ll publish a post on the amazing escape artistry slime mold is capable of soon: click here for the post).
- How to optimize humidity levels in the petri dishes: putting a small piece of wet white paper towel or sponge in the plates for instance.
- Whether cheap plastic wrap is enough to keep humidity in, or whether parafilm would be better. Plastic wrap is easy to pull off and back on. Parafilm a little less so, but should do a much better job of sealing the humidity in.