Silicon Structures That Form Like in Children's Pop-Up Books

John Rogers was evidently not content with making electronics bendable, enabling them to potentially be used for actively conformable to the human body. The University of Illinois, who went on to found flexible electronics firm MC10 (Cambridge, MA) has a new trick up his sleeve: converting tiny 2-D silicon structures into 3-D.

The mechanism used to do that bears a resemblance to children's pop-up books, but instead of using paper and cardboard, the researchers used silicon as a substrate. The resulting shapes are in the microscopic, even nano, range.

Applications of the breakthrough include everything from electronics and batteries to medical devices. Examples of the latter include creating electronic scaffolds for guiding and monitoring tissue culture growth. In addition, the 3-D structures could be as networks for flexible electronic systems that can bend to accommodate the contours of the human body. The advance could also potentially enable the development of smart structures that imitate active processes of organisms.

Rogers team at the University of Illinois at Urbana-Champaign succeeded in geometrically converting 2-D micro/nanostructures into 3-D geometries using a mechanism similar to those used in children's 'pop-up' books.

In medicine, such 3-D geometry could lay the groundwork for developing structures that interface with the natural geometries of the body. While other means of creating 3-D structures exist, their scope is limited in terms of materials and geometries compatible with them, according to a press release from the university.

Rogers says the technique also offers advantages over standard 3-D printed shapes because that process lacks "the ability to build microstructures that embed high performance semiconductors, such as silicon."

The researchers can fashion 3-D geometries in nearly any material, including those used in photonics and electronics. The researchers tested more than 40 geometries in experimental and theoretical studies, including single and multiple helices, toroids, and conical spirals. The resulting shapes resemble spherical baskets, cuboid cages, starbursts, flowers, tents, scaffolds, fences, and frameworks.

To make the 'pop-up' shapes possible, the researchers used flexible substrate that receives force at precise locations in a 2-D material to cause a controlled buckling.

"Releasing the substrate to its original shape induces buckling processes that lift the weakly bonded regions of the 2-D structure out of contact with the surface," says Sheng Xu, a postdoctoral fellow at the university. "The resulting spatially dependent deformations occur in an ordered sequence to complete the 3-D assembly."

Brian Buntz is the editor-in-chief of MPMN and Qmed. Follow him on Twitter at @brian_buntz.

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