Schrödinger's Kitten

Irreverent Science for Everyone

Thursday 05 January 2017

Shape change in nature and human attempts to emulate it: now with VIDEOS

  • micro
  • mywork
  • materials

How do sea cucumbers manage to be both flexible and firm? How does a plant build up enough energy, just from drying out, to fire its seeds five times its own length? Why don't clams get tired of holding themselves shut? These questions all boil down to 'how do natural materials change shape', and it's a bloody good question if you want to make synthetic materials change shape.

Making synthetic materials change shape could mean:

  • having products that do more than one thing
  • having valves, covers and inlets that respond to their environment as easily and elegantly as a pinecone does
  • responsive tech that is inherently unhackable and disaster resistant
  • soft robots!!

We are not there yet. And there's a lot of work to be done. Hackers, makers, amateurs, artists, and bodgers have helped the field of 3D printing (and many other technologies) along a lot, and so I reckoned they have a lot to contribute here. So, I gave the talk 'Shape change in nature, and puny human attempts to emulate it' to a load of them in a field in central England at Electromagnetic Field 2016.

Electromagnetic Field is a hacking/making festival with workshops, talks, discos, installations, and all sorts of things. It is for people who are interested in stuff, where stuff might be playing 'No limits' on your arm, firepong, brewing, recommender systems, the history of records on x-ray film, hacking toys, computation in biology, or indeed shape changing materials.

This is a subject dear to my heart as my PhD is in 3D printing materials that change shape. A recording of the talk is on Youtube, but if you watch it (or if you were there), you'll notice that the videos I was going to show don't work! So here I'm posting the videos I would have shown and what I would have said about them. I also wrote a paper about it if you prefer reading to vids.

My talk

Natural shape change examples: plant solar tracking

This is a timelapse video of a Cornish Mallow leaf moving to maintain the optimum angle to the sun. It does vector maths and logic operations with its leaves. This is work by Michael Dicker and colleagues at Bristol; they are using photoresponsive hydrogels to build a robot that moves like this plant.

Degrees of shape change: step by step

This is about tuning the responses of materials that are sensitive to heat to have multiple stages of deployment, one after the other. Here there are two shape memory polymers with different transition temperatures, and depending on the ratio in which they are mixed the transition temperature of the mixture will be at a different place between the two extremes. This is a self-folding box.

Volume changing modular origami

Combining pneumatic and 'snapology' origami approaches, this is an array of cubes that can be inflated, deflated and collapsed to change their orientation, volume and stiffness.

Relatedly: Totally unpowered passive origami, showing auxetic (non-constant-volume) collapse.

Constrained swelling (aka doing it pinecone style)

This is a hydrogel which swells when wet. It, however, can't swell as much in the direction that it was printed, because tiny cellulose fibres were aligned that way during printing. Using the fact that it swells more in the direction perpendicular to the print direction, and different spacings of the lines giving a stronger or weaker gradient, they can encode complex curvatures into a spiral grid print. They also have the maths chops to do the inverse problem: take a curvature, such as those of flowers, and back-construct what needs to be printed to make something fold into that. This is closest to my work, except theirs works.

What can hackers contribute?

I've wrapped up with some hypothetical ideas of what people interested in design, 3D printing or mechanisms could contribute to shape changing technology. If this is something that interests you, there's a section on it at the end of the Open Access1 paper I wrote: 'Morphing in Nature and Beyond', for the Journal of Materials Science.

This reviews some of the examples I gave, and a few more, in more detail. In the paper I go through some useful shape changing materials, pull out some common characteristics of them, and compare them to synthetic materials with a similar mode of operation. There's some material about how they work and methods of modifying their response, in degree or direction. Different methods of triggering shape change response are mentioned, and then I discuss ways of structuring these materials to direct their expansion or contraction, or make better use of it. It's quite a broad topic so there's also a lot of pointers to reviews in specialist areas!

It's available for free with open access funding provided by the University of Bristol.

Sorry this writeup is late, I gave this talk and then ended up pingponging round the world for conferences — now just found this writeup and thought 'better posted than never'.

Many thanks to Electromagnetic Field for having me: it was a great opportunity to speak and attend, where I got over my nervousness about surface mount soldering, sat in a very large hammock, did some great whisper karaoke, learnt the connection between conductive paint and ghosts, and discovered the existence of Shannon's Robotic Mouse.

Many of the talks at Electromagnetic Field can be found on their Youtube, so do have a look. The next EMF will take place in 2018, and the next similar event in Europe is SHA2017 in the Netherlands.

1. Open access means you are able to read the work your tax money paid for. Yes, this is a novel idea.

Content: Scary Boots — Design: Canis Lupus