Ink-Based Origami Structures Could Be Next Biocompatible Devices

Origami structures made from printed sheets of titanium hydride ink could form the basis of future 3-D structures. Developed by materials science and engineering professor Jennifer Lewis and a team of researchers at the University of Illinois (Urbana-Champaign), the complex structures could eventually play a role in the fabrication of biocompatible devices, microscaffolding, and other microsystems.

As presented in the online edition of the journal Advanced Materials, the researchers' work employs a large printer to deposit inks containing metallic, ceramic, or plastic particles to assemble a structure layer by layer. Then, the structure is annealed at a high temperature to evaporate the liquid in the ink and bond the particles, leaving a solid object. However, as more layers are added, the lower layers tend to sag or collapse under their own weight. To rectify this problem, the scientists print a flat sheet and then roll it up into a spiral or an assortment of other shapes.

"Most of our inks are based on aqueous formulations, so they dry quickly," Lewis explains. "They become very stiff and can crack when folded." Hence, the scientists sought a solution that would render the printed sheets pliable enough to manipulate yet firm enough to retain their shape after folding and during annealing. They solved this problem by mimicking wet-folding origami, in which paper is partially wetted to enhance its foldability. By using a mixture of fast- and slow-drying solvents in the ink, the sheet dries partway but stays flexible enough to fold through multiple steps.

By combining printing and origami techniques, the scientists were able to achieve a material with structural complexity that cannot be attained by direct-printing methods alone. In addition, the team can print sheets with a variety of patterns, adding yet another level of detail. "By combining these methods, you can rapidly assemble very complex structures that simply cannot be made by conventional fabrication methods," Lewis says.

The team hopes to expand its origami repertoire to include much larger and much smaller structures based on an expanding array of inks. For example, the method can be extended to a variety of other ceramics and metals, including steels, nickel- and cobalt-based alloys, and refractory and noble metals. They also plan to explore possible applications, including lightweight structures, biomedical devices, sensors, and other components.