Toys demonstrating how biological machines move

By connecting tiny self-propelled toys in a chain, researchers at the UVA Institute of Physics have found a key to studying the movement of microscopic organisms and the molecular motors inside our cells.

The microbot ‘Hexbug Nano v2’ uses vibrations to propel itself forward. By connecting several of these toys with elastic silicone rubber chains, the resulting structure is ‘elastoactive’. This means that it will return to its original shape after being deformed, while the self-moving active constituents that comprise it are constantly trying to push the structure in a certain direction.

Depending on the size of the links and whether the chain is attached to one or both ends, elastoactive chains exhibit different types of motion, incl self oscillate, self sync And snapped at himself.

“By experimenting with these elastoactive chains, we found that there is an interaction between activity and elasticity: when activity predominates, the chains self-oscillate and are synchronized,” says Corentin Coulais, head of the Mechanical Materials Laboratory at the University of Amsterdam.

He continued: “Mechanical automatic oscillations and synchronizations are key features of biological machines, features useful for creating new types of autonomous robots. This active chain really allows us to distinguish the nature of these nonlinear phenomena.”

Self-oscillation, self-synchronization and self-snapping

When a structure is self-oscillating, this means that it bends back and forth on itself. In chains, microbots might start by bending the chain to the left. However, because the chain is pinned at one end, the elastic joints resist this movement, redirecting the boot in such a way that it begins to push and bend the chain to the right. This movement will again be held by the elastic chain, until the boot starts moving to the left again.

Synchronization occurs when two elastoactive chains are connected at one end by a rod that is sufficiently rigid. By squirming, the two linked chains automatically began to oscillate at the same frequency, like seaweed being moved by the same wave.

Finally, taking one elastoactive chain and pinning both ends, it exhibits a ‘self-snapping’ behavior. When you bend a playing card with your finger, you can make it ‘snap’ to bend the other way by pushing hard enough from the side. The elastoactive chain does this on its own, repeatedly snapping from a left bend to a right bend.

Instructive game

“We started this research by just playing with microbot toys. But more generally, the idea is to explore materials beyond equilibrium. In soft matter, active fluids have been studied extensively in the last 25 years, but their solid counterparts have been investigated far less,” said Coulais.

Later on the menu explores elastoactive behavior on smaller scales, for example in so-called colloid systems, which are made up of tiny particles suspended in a liquid. Although these are still model systems, they are much closer to biological systems due to the similar length scales and the presence of fluids. At any scale, it can also be interesting to use intelligent design to embed multiple independent oscillations in a single structure to achieve more complex movement patterns. With a better understanding of self-oscillation, the hope is that it will be possible to create new types of autonomous robots.