3-D printing is radically transforming fields ranging from jewelry-making to jet engine fabrication. Now innovators are moving beyond the production of solid, static objects to create materials that can be transformed and manipulated at will. Using a 3-D printer, engineers have fabricated a new soft material with a modifiable surface texture. The researchers who designed this material have suggested a wide array of applications for such surfaces but the original inspiration for their shape-shifting creation was the cuttlefish.
“The project was originally about camouflage,” says lead author Mark Guttag, a PhD student at Massachusetts Institute of Technology who conducted this study as part of his master’s thesis. Cuttlefish are cephalopods with large, elongated bodies and tentacles around their mouths. They often hide from predators by altering skin color and patterns to closely blend in with their surroundings. Even more intriguingly, they can match their skin’s texture to that of surrounding surfaces. Octopuses and other cephalopods similarly camouflage themselves.
Inspired by these aquatic masters of disguise, Guttag and co-author Mary Boyce, dean of engineering at Columbia University, wanted to create their own artificial surfaces with adjustable textures. To do so, they developed a 3-D printing process that uses two types of polymers: one rigid, one flexible. The printer inserts an array of the rigid polymers into a bed of squishy material composed of the more flexible type. When the material is compressed, its naturally smooth surface takes on a patterned texture that depends on the spacing and shapes of the embedded rigid polymers. It can be smooth, ridged, bumpy or even form more complicated patterns. When the material is released, it reverts to its original smooth texture.
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Shengqiang Cai, an engineer at the University of California, San Diego, who was not involved with this study, says that Guttag and Boyce’s material is “innovative and inspiring.” According to Cai, the creation of this method for creating modifiable surfaces not only has many important applications for surface engineering but may also provide valuable insights into the underlying mechanics of biological surface patterning.
Once the material is printed, its rigid polymers are stuck in a fixed array and cannot change positions relative to one another. But Guttag and Boyce have proposed a number of means for achieving different types of surfaces from the same sheet of printed material. For example, by using elongated rigid polymers instead of spherical ones, scientists could create surfaces that are smooth along one direction but ridged in the opposite direction. Some rigid polymers might yield differently textured surfaces depending on the strength of the applied force. If they are lightly squeezed, they form one texture, but further compression would cause the polymers to rotate relative to one another, creating a different topography. Other polymers could swell or shrink relative to the soft material.
In the sample Guttag and Boyce printed to physically test their code, the rigid polymers were about a centimeter in diameter and the bed of soft material was about a meter across. But according to Guttag, their printing process could be scaled up or down, depending on the material’s intended use. “The main thing is the relative sizing of particles and relative spacing of them, as opposed to the absolute size,” he says.
The team also has discovered their modifiable surfaces are not only useful for camouflage but a spectrum of other applications such as making an object more or less aerodynamic, reflective or water-repellent. These surfaces might also be useful for controlling fluid flow. It seems transformable topographies might bring the 3-D printing revolution to a host of new industries.
