A research team headed by Professors Michael Dickey and Jan Genzer has developed a process whereby the sequential folding of two-dimensional plastic sheets can be programmed as they self-transform into three-dimensional objects. In 2011, the researchers were early pioneers in the field of self-folding 3-D structures.
In the 2011 work, pre-stressed plastic sheets were run through a conventional inkjet printer to print bold black lines on the material. The material was then cut into desired patterns and placed under an infrared light. The black lines absorb more energy than the rest of the material, causing the plastic to contract – creating hinges that fold the sheets into 3-D shapes.
A modest amount of control over the folding sequence was accomplished by varying the thickness of the black lines, but that wasn’t adequate to produce complicated shapes. According to Dr. Dickey, “A longstanding challenge in the field has been finding a way to control the sequence in which a 2-D sheet will fold itself into a 3-D object.” “And as anyone who has done origami – or folded their laundry – can tell you, the order in which you make the folds can be extremely important.”
“The sequence of folding is important in life as well as in technology,” says Dr. Jan Genzer. “On small length scales, sequential folding via molecular machinery enables DNA to pack efficiently into chromosomes and assists proteins to adopt a functional conformation. On large length scales, sequential folding via motors helps solar panels in satellites and space shuttles unfold in space………”.
In the new work, the folding sequences of the sheets are controlled precisely by printing lines of different colors, which selectively absorb light of different wavelengths.
When the colored regions absorb light, the light gets converted into heat that increases the local temperature of the printed regions on the sheet. The sheet, in turn, shrinks gradually across its thickness in the printed-light-absorbing regions (due to relaxation of the strain), which act as hinges along which the sheet folds. This enables the researchers to trigger any of the folds in any order.
The key here is the selective/differential absorption of different wavelengths of light by different colors printed on the sheet. A video of the sequential folding techniques in action can be seen at https://youtu.be/ZlZOdiwbZIE.
As related by Dr. Genzer, “We’re very proud of this work, not only because it is, to the best of our knowledge, the first demonstration of this programmed sequential folding but also because the idea was driven by young researchers working in Michael’s and my labs. Ying Liu, at that time a graduate student (now a postdoc), was the primary driver behind the technology. Importantly, Brandi Shaw, a CBE undergraduate student, contributed substantially to this effort and worked effortlessly alongside Ying. Brandi graduated from NC State’s CBE department in May 2014.”
The first paper to report the work, “Sequential Self-folding of Polymer Sheets,” is published in the AAAS journal Science Advances. Dr. Liu is the lead author of the paper. The paper was co-authored by Ms. Shaw, and Professors Dickey and Genzer are co-corresponding authors.
The work was accomplished with support from the Emerging Frontiers in Research and Innovation (EFRI) program through the National Science Foundation, under grant number 1240438.