A new way of printing and folding ceramic and metal lattices into miniature structures could lead to novel lightweight engineering structures. The technique involves making latticed sheets from ceramic ink, then folding and heating these sheets to create intricate shapes. The method could be used to make lightweight parts for aerospace applications, complex scaffolds for tissue engineering, and filters and catalysts for industrial chemical production.

"We can make complex, three-dimensional shapes that can't be made in other ways," says Jennifer Lewis, director of the Materials Research Laboratory at the University of Illinois at Urbana-Champaign. Lewis developed the technique with Illinois researcher Bok Ahn and David Dunand, a professor of materials science at Northwestern University. The researchers say it fills a need for a way to fabricate complex structures on the centimeter scale--too small for conventional molding or machining, and too big for lithography or similar techniques.

Lewis has previously created new kinds of inks and printing methods for making two-dimensional structures. Her approach involved squeezing inks containing ceramic or metal particles out of a print head, similar to the way toothpaste would be squeezed from a tube. With these inks, Lewis could make latticed patterns, one layer at a time. The lattices could then be heated to fuse the particles together and remove the ink solvents.

Lewis's group turned to origami folding when a collaborator asked her to make concentric cylinders of titanium for use in tissue engineering, as implants to encourage bone growth. Ahn realized that such a structure could be made by rolling up a printed lattice before it heating it, and the group tinkered with the formulation of the inks to better suit the process. The material is elastic enough to fold, but sturdy enough not to droop or crack before it's solidified.

The same technique has now been used to make complex structures that include an origami crane requiring 16 folding steps. The crane has no practical application, but demonstrates the advantages of this technique, the researchers say.

The print-and-fold technique "allows you to create the shape you want, but with the weight taken out," says Bob Peterson, senior scientist at Aerojet, an aerospace company headquartered in Sacramento, CA, that is not affiliated with the Illinois group.

Peterson says the technique might be used to make, for example, lighter titanium reinforcing struts for rocket wings, and he estimates that the Illinois group's manufacturing technique could reduce the weight of these particular parts from about 1.5 pounds to a quarter pound. Instead of making a solid titanium cube, for example, researchers could build a hollow one with much less material. The folded metal and ceramic structures should also be able to withstand extreme temperatures and heavy loads, which is important for aerospace and industrial applications.

The Illinois researchers are working with a wider range of materials, and testing the mechanical properties of the structures they have already made. The titanium structures, says Dunand, are strong and fracture resistant. He adds that the approach should be compatible with a range of materials besides titanium, including steel and other metals, many ceramics, and the compounds used to make zeolites, which are commonly used for filtration and catalysis.