“A longstanding challenge in the field has been identifying a method to regulate the sequence in which a 2-D sheet will fold itself into a 3-D object,” says Michael Dickey, a lecturer of chemical and biomolecular engineering at NC State and co-corresponding author of a study describing the work. “And as anyone who has done origami, or folded their laundry, can tell you, the order in which you make the folds can be highly vital.”
“The sequence of folding is vital in life as well as in technology,” says co-corresponding author Jan Genzer, the S. Frank and Doris Culberson Distinguished lecturer of Chemical and Bio-molecular engineering at NC State. “On small length scales, sequential folding through molecular machinery allows DNA to pack effectively into chromosomes and assists proteins to adopt a functional conformation. On large length scales, sequential folding through motors helps solar panels in satellites and space shuttles unfold in space. The advance of the present work is to induce substances to fold sequentially using just light.”
Particularly, the scientists have introduced a method to design and engineer 2-D substances that can be regulated remotely in order to trigger any of the given folds to take place, in any order. Genzer and Dickey were early leaders in the group of self-folding 3D structures. In their landmark 2011 paper, the scientists outlined a method in which a pre-stressed plastic sheet was run through a traditional inkjet printer to print bold black lines on the substance. The material was then cut into a desired design and placed under an infrared light, like a heat lamp.
The printed lines absorbed more energy than the rest of the substance, causing the plastic to contract, preparing a hinge that folded the sheets into 3D shapes. By varying the width of the hinges, or printed lines, the scientists were able to alter how far and how swiftly each hinge folds. The method is compatible with commercial printing methods, like screen printing, roll-to-roll printing, and inkjet printing, that are cost-effective and high throughput but inherently 2D.
The novel advance employs essentially the similar method, but takes benefit of the fact that distinct colors of ink absorb distinct wavelength, or colors of light. “By printing the hinges in distinct colors, we can regulate the order of the folds by altering the wavelengths of light that shines on the 2-D sheet,” says Genzer.By manipulating the colors of ink, the scientists were also able to get hinges to fold sequentially when exposed to a singular wavelength of light.
“This is a proof of concept, but it opens the opportunities to a range of potential application using a simple and cost-effective process,” says Dickey. “Eventually, people are keen in self-organizing structures for numerous reasons, from shipping things in a flat package and having them organized on site to having devices self-assemble in clean environments for electronic or medical applications.”
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