No assembly required

Materials World magazine
,
3 Jul 2015

From furniture that requires no hex key, to folding robots and the manufacture of carbon nanotubes. James Perkins reports on the rise of self-assembly.

It is easy to get carried away when thinking about self-assembly. The universe and life as we know it has randomly put itself together after billions of years of particles bumping into each other.

So what if we could harness this power for our own ends, to make life easier and more efficient? It is something that designers, architects, engineers and scientists have been thinking about seriously for at least two decades.

The imagination runs wild with the possibilities, but let’s stick to what is happening today, which ranges from research into self-assembly at the nanoscale, to furniture and autonomous robots at the macroscale.

Skylar Tibbits, director of the Self Assembly Lab at the Massachusetts Institute of Technology, is inspired by biological processes such as the formation of complex folding proteins from amino acids. He coined the term 4D printing, which uses 3D printing to produce materials that change with time and circumstance. 

He believes self-assembly is a new tool in the belt of how we make things at all scales, whether tinkering, or high-precision industry applications.

In a paper entitled Self Assembly and Nanostructured Materials, authors George Whitesides, Jennah Kriebel and Brian Mayers describe self-assembly as the bridge between bottom up (molecular synthesis) and top down (lithography) strategies.

In 2006, Bernadette Bensaude-Vincent, Associate Professor of Epistemology, History of Science and Technology at Pantheon-Sorbonne University, France, described self-assembly as ‘spontaneous arrangements of small building blocks in ordered patterns or structures’.

She said, ‘Self-assembly is extremely advantageous from a technological point of view, because it is a spontaneous and reversible process with little or no waste, and a wide domain of applications ranging from nucleation of inorganic particles, formation of vesicles, monolayers [and] supramolecules’.

A part of the furniture

Furniture seems a popular medium for self-assembling technology, perhaps because people are so tired of assembling it from a flat pack. Belgian designer Carl de Smet calls his furniture self-reconfiguring, rather than self-assembling. The polyurethane memory foam he uses can be compressed to a fraction of its final size, before being heated at 70˚C to return to its original shape. 

De Smet jokes that the only thing holding his technology back is the fact that not many houses have saunas. ‘At the moment, it is a case of first buy a sauna, then buy the seat, but otherwise it won’t work. It is a challenge to develop a flexible heating system that has equal material properties to the foam and that we can embed during the moulding process.’ He is working on this and hopes to have the process working next year.

De Smet’s research started at Belgium’s Katholieke Universiteit Leuven in 2002, when he was looking into shape-memory alloys. He wanted to bring them to a larger scale, but found the process was too energy intensive. He moved to shape-memory polymers, but the plastic was not strong enough to lift its own weight against gravity. Foam was the next logical step in the search for the right material.

Ideally, if de Smet’s invention revolutionises furniture, packaging will no longer be required and delivery will be more efficient. But he admits the chair was a symbolic blueprint and there are other applications that could be more promising.

‘We are now doing studies on grafts and splints. If you break your arm, our material could close itself around the arm, rather than having to put together a splint. Also, you wouldn’t have to break the case to get it off and it could be re-used.’

Meanwhile, scientists at the EPFL Biorobotics Laboratory at Lausanne, Switzerland, have developed modular, self-assembling robots that one minute could make a chair, the next a table.

Each module is a cube with rounded corners comprised of two parts, joined along the diagonal axis, which allows the cube to rotate along that axis. Each of the six flat surfaces has a motorised plate that allows the module to grip using a retractable claw system and also spin on that surface.

Auke Ijspeert, Associate Professor at the Biorobotics Laboratory, hopes the modular robot system can be used in many applications. ‘The main one we have in mind is as an assistive technology for the elderly or those who are not able to move properly. They could have an apartment that will have furniture that helps the person – for instance, the table approaching the person to bring them medicine or a glass of water.’

Inspirational origami

The centuries-old paper folding art of origami could hold valuable insights for those scientists pushing the boundaries of self-assembly. At Harvard University’s Wyss Institute the research into self-folding robots developed out of a team’s belief in the potential of origami-inspired manufacturing due to the ease of making flat structures and folding them to produce complex geometries and mechanisms.

The study’s lead author, Sam Felton, says, ‘We've made a couple robots this way and found the slowest part of the building process was when the robot was folded by hand. So we looked for ways to get the robots to fold themselves.’ 

The robot the team created is the first fully-autonomous self-folding machine. 

‘There has been a lot of interesting and varied work on self-folding,’ says Felton, ‘but most of it is demonstrated on relatively simple shapes, without moving parts. By integrating electronics and using patterns derived from computational origami, we were able to apply these self-folding techniques to machines.’

The goals are to make the self-folding more reliable by using better materials and new fold geometries, and to expand the range of possible sizes of the machines.

The robot is mostly paper and prestretched polystyrene, which is sold commercially as Shrinky-dinks. There is also a flexible circuit board made of a thin plastic film and copper. The motors, batteries and some of the circuit components are shop bought.

Combining the technology with 3D printing unlocks more possibilities. Felton says, ‘One great example is the battery. In our case, we installed it by hand, but another lab at Harvard, the Lewis Group, can now 3D-print batteries, so in the future, our robots could have batteries printed directly onto their bodies.’

Where self-assembly could have the biggest impact is at the nanoscale. New materials, such as graphene, offer almost endless possibilities, but scientists are still working out how to manufacture them efficiently. Here again, origami is an inspiration.

Empa scientists, working under the direction of Roman Fasel, Professor of Chemistry and Biochemistry at the University of Berne, and alongside researchers from Max Planck Institute for Solid State Research, made a breakthrough towards the end of 2014 in the manufacture of carbon nanotubes through self-assembly. 

In the first step, the initial molecule is placed upon a hot platinum surface and it folds, origami-like, into a 3D object, called the germling. The team manipulates the folding by splitting off hydrogen atoms at precise locations, allowing carbon-carbon bonds to form in their place.

The molecule folds into a rounded cap, with the open end lying on the platinum surface. Carbon atoms are added to this end through the decomposition of ethylene (C2H4) on the platinum surface and the tube grows.

The team grew more than 100 million nanotubes per square centimetre, but only a small proportion was fully grown with matching characteristics. 

The question Fasel and his colleagues want to answer is this – which processes are responsible for the formation of the fully-grown nanotubes, and how can the yield be increased? This is just one of the many exciting possibilities self-assembly holds  at the nanoscale.