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article imageEssential Science: Graphene makes for cell-sized robots

By Tim Sandle     Jan 8, 2018 in Science
Imagine an electricity-conducting, environment-sensing, shape-changing cell-sized machine, used for medical diagnosis. Impossible? Not according to new research that has harnessed the properties of graphene.
The new concept comes from Cornell University researchers, who have devised a type of robot exoskeleton which can quickly change its shape as it senses chemical or thermal changes in the environment.
Such microscale robots can be fitted with electronic, photonic and chemical payloads, useful for a variety of biomedical tasks. In terms of how small these devices are, they are around the size of a microorganism.
According to one of the lead researchers Dr. Itai Cohen, the new robots are very powerful: “You could put the computational power of the spaceship Voyager onto an object the size of a cell.” An added benefit is the strength of the graphene which means the robot can be subject to a range of different environments.
Making a superlattice with patterns of hydrogenated graphene is the first step in making the materia...
Making a superlattice with patterns of hydrogenated graphene is the first step in making the material suitable for organic chemistry. The process was developed in the Rice University lab of chemist James Tour.
Tour Lab/Rice University
Graphene, a hot topic on Digital Journal’s science pages, is a single atom thick layer of a carbon. The material is transparent, at least as strong as steel, and it possess many remarkable properties, such as being highly conductive of electricity.
While it has been possible for a while to develop very tiny, very powerful machines they have not possessed the ability to move or to react to changes in their external environment. This has now been made possible using a special motor termed a bimorph.
A bimorph is an assembly of two materials, in this case: graphene and glass. The material can alter its shape (bend) when subject to a stimulus such as heat, chemicals or when subjected to an applied voltage. The material changes its shape because the two materials have different responses. With heat, for instance, graphene and glass have differing thermal responses. This means they expand by different levels when they are exposed to the same temperature change.
With chemicals the bimorphs fold in response to chemical stimulus. This through large ions being passed into the glass, causing the glass to expand. This happens, for example, when the outer edge of glass is submerged into a ionic fluid, with the activity taking place at the nanoscale.
When the bimorph bends to relieve physical strain this enables one layer to stretch out longer than the other. Taking this concept, the researchers added rigid flat panels that cannot be bent through the bimorphic reaction. Where these are positioned in specific places the researchers were able to create different folding structures. The structures ranged from tetrahedra (triangular pyramids) to cubes.
The system was developed using the technique of atomic layer deposition. This involves chemically layering atomically thin layers of silicon dioxide onto aluminum. This is followed by wet-transferring a layer of graphene (just one atom thick) onto the stack.
In one trial, the researchers developed a device just three times larger than a red blood cell, when it is folded.
The findings have been published in the journal Proceedings of the National Academy of Sciences. The research paper is headed “Graphene-based Bimorphs for Micron-sized, Autonomous Origami Machines.”
Essential Science
First static fire test of a Falcon Heavy center core completed at The SpaceX McGregor  TX rocket dev...
First static fire test of a Falcon Heavy center core completed at The SpaceX McGregor, TX rocket development facility on May 9, 2017.
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we looked at how 3D printing is being used to develop parts for rocket engines.
The week before we looked into research into to the human microbiome, highlighting a connection between an imbalance of microorganisms in the human gut and feelings of despair.
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