Geometric Shapes Fold Themselves into Microscopic Building Blocks
A few of the 2.3 million possible 2-D designs for a truncated octahedron (right column). The question is: Which net is best to make a self-assembling shape at the nanoscale?
CREDIT: Shivendra Pandey/Gracias Lab, Johns Hopkins University
A tiny, self-folding dodecahedron may do more than impress an origami master. Inspired by self-assembling viruses and proteins, such dust-size 3D shapes could someday deliver medical drugs inside the human body or join together to build new electronic devices.
That possible vision comes from experiments that used flat nickel plates soldered together to form 2D configurations. When heated to about 360 degrees Fahrenheit (182 degrees Celsius), surface tension between the solder and plates caused the hinges to fold upward and rotate to become geometrically complex 3D shapes possible building blocks for a new world of microscopic manufacturing.
"This is about creating basic tools in nanotechnology," said Govind Menon, a mathematician at Brown University. "It's important to explore what shapes you can build. The bigger your toolbox, the better off you are."
Scientists have previously created small, self-assembling 3D shapes from simpler structures such as cubes. But they had more trouble nailing the right 2D configurations to make more complex 3D shapes found in nature. For instance, viruses use protein shells shaped like dodecahedrons consisting of 12 equal pentagonal faces to protect their genetic material.
To puzzle out the problem, Menon and his Brown University colleagues worked with shapes somewhat larger than nanoscale objects that range between 1-and-100 nanometers. A human hair is about 100,000 nanometers wide.
By building computer models, researchers came up with six 2D configurations that seemed likely to work as self-folding 3D structures. They then tested the shapes with colleagues from Johns Hopkins University and saw that the 2D configurations did successfully fold up and seal themselves into complex 3D shapes.
"What's amazing is we have no control over the sequence of folds, but it still works," Menon said.
Such success opens the door to building shapes such as truncated octahedrons with 14 total faces six squares and eight hexagons. Figuring out the best self-folding 2D configurations for truncated octahedrons would usually require researchers to sift through 2.3 million combinations.
The full study is detailed in the journal Proceedings of the National Academy of Sciences.