A fully functional nanosized robot requires electronic circuits, photovoltaics, sensors, and antennas. But if the robot needs to move, it must be able to bend. Researchers have created micron-sized shape memory actuators that enable atomically thin two-dimensional materials to fold themselves into 3D configurations. All they require is a quick jolt of voltage. And once the material is bent, it holds its shape even after the voltage is removed.
Imagine a million fabricated microscopic robots releasing from a wafer that fold themselves into shape, crawl free, and go about their tasks, even assembling into more complicated structures. The robots’ shape memory actuator can drive with voltage and hold a bent shape.
The actuators can bend with a radius of curvature smaller than a micron — the highest curvatures of any voltage-driven actuator by an order of magnitude. This flexibility is important because one of the basic principles of microscopic robot manufacturing is that the robot size is determined by how small the various appendages can be made to fold. The tighter the bends, the smaller the folds, and the tinier the footprint for each machine. It’s also important that these bends can be held by the robot, which minimizes power consumption — a feature especially advantageous for microscopic robots and machines.
The devices consist of a nanometer-thin layer of platinum capped with a titanium or titanium dioxide film. Several rigid panels of silicon dioxide glass sit atop those layers. When a positive voltage is applied to the actuators, oxygen atoms are driven into the platinum and swap places with platinum atoms. This process, called oxidation, causes the platinum to expand on one side in the seams between the inert glass panels, which bends the structure into its predesignated shape. The machines can hold that shape even after the voltage is removed because the embedded oxygen atoms bunch up to form a barrier, which prevents them from diffusing out.
By applying a negative voltage to the device, the researchers can remove the oxygen atoms and quickly restore the platinum to its pristine state. And by varying the pattern of the glass panels — and whether the platinum is exposed on the top or bottom — they can create a range of origami structures actuated by mountain and valley folds.
The tiny layers are about 30 atoms thick, compared to a sheet of paper that might be 100,000 atoms thick. The machines fold themselves within 100 milliseconds. They can also flatten and refold themselves thousands of times. And they only need a single volt to be powered to life.
The team is currently working to integrate the shape memory actuators with circuits to make walking robots with foldable legs as well as sheet-like robots that move by undulating forward. These innovations may someday lead to nanorobots that can clean bacterial infection from human tissue, micro-factories that can transform manufacturing, and robotic surgical instruments that are ten times smaller than current devices.