Origami on the microscopic

Dutch researchers have taken the ancient art of origami down to the microscopic level, folding flat sheets of silicon nitride into cube, pyramids, bowls and long triangular structures with only a drop of water. The shapes can be folded and unfolded multiple times without wear, and these tiny self-assembling forms could be used a tools to deliver drugs to targeted areas of the body, or to perform autonomous microsurgery. “While making 3D structures is natural in everyday life, it has always been extremely difficult to do so in microfabrication, especially if you want to build a large number of structures cheaply,” said Antoine Legrain, graduate student at the University of Twente. Research focussed on the technique of self-assembly, in which natural forces such as magnetism or surface tension trigger a shape change. In this study they used water to activate and control folding. “Water is everywhere, is biocompatible, cheap and easy to apply,” said Legrain. A custom software program was used to design the flat starting pattern before being printed on silicon wafers. Hinges were created by researchers etching away material before depositing a thinner layer. “Possible shapes are in principle limitless,” said Legrain, “as long as they can first be made on a flat surface.” Folding happened after researchers pumped a small amount of water thought a channel they’d left in the silicon wafer. Capillary forces created by water molecules sticking to each other and to the silicon pulled the flat surfaces together to form fully 3D creations. The shapes could be opened and closed up to 60 times without signs of wear as long as they stayed wet. This ability could be useful in biomedical applications where tiny self-folding tools could deliver drugs exactly where they are needed in the body, or grab tiny amounts of material for micro-biospies. Controllable elastocapillary folding of three-dimensional micro-objects through-wafer filling This video shows how a flat design folds into a cube with the addition of water.  The researchers can fold and unfold the cube multiple times without wear, as long at the structure remains wet. Credit: Journal of Applied Physics/A. Legrain, et. al, University of Twente https://www.youtube.com/watch?v=Q0r1cvKeQtw