Shape-changing cell-sized robots in the offing

New York: Scientists are developing electricity-conducting, environment-sensing, and shape- changing robots the size of a human cell.  Researchers at Cornell University in the US created a robot exoskeleton that can rapidly change its shape upon sensing chemical or thermal changes in its environment. 

These microscale machines - equipped with electronic, photonic and chemical payloads - could become a powerful platform for robotics at the size scale of biological microorganisms, they said.  "We are trying to build what you might call an 'exoskeleton' for electronics," said Paul McEuen, professor at the Kavli Institute at Cornell. The machines move using a motor called a bimorph. 

A bimorph is an assembly of two materials - in this case, graphene and glass - that bends when driven by a stimulus like heat, a chemical reaction or an applied voltage. The shape change happens because, in the case of heat, two materials with different thermal responses expand by different amounts over the same temperature change.

As a consequence, the bimorph bends to relieve some of this strain, allowing one layer to stretch out longer than the other. By adding rigid flat panels that cannot be bent by bimorphs, the researchers localise bending to take place only in specific places, creating folds.  With this concept, they are able to make a variety of folding structures ranging from tetrahedra (triangular pyramids) to cubes. In the case of graphene and glass, the bimorphs also fold in response to chemical stimuli by driving large ions into the glass, causing it to expand.

The bimorph is built using atomic layer deposition - chemically "painting" atomically thin layers of silicon dioxide onto aluminum over a cover slip - then wet- transferring a single atomic layer of graphene on top of the stack. The result is the thinnest bimorph ever made. 

One of their machines was described as being "three times larger than a red blood cell and three times smaller than a large neuron" when folded. Scaffolds of this size have been built before, but this group's version has one clear advantage. "Our devices are compatible with semiconductor manufacturing. That is what is making this compatible with our future vision for robotics at this scale," said Cornell University physicist Itai Cohen.