In a blink of an eye, an octopus can transform from a colorful creature to a drab pile of rocks and plant life, indistinguishable from the surface it’s perched on.  This camouflage relies on specialized pigment organs, but what makes the octopus unique among animals is its ability to change the texture of its skin. Previously flat stretches can bulge out in patterns that complete the illusion.

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James Pikul, an assistant professor of mechanical engineering and applied mechanics in the University of Pennsylvania’s School of Engineering and Applied Science, is taking inspiration from these and other cephalopods, developing a deeper understanding of the physics that allow 2-D surfaces to transform into 3-D shapes.

In a paper published in the journal Science, Pikul and co-authors outlined a method for achieving this transformation that they have dubbed CCOARSE, or Circumferentially Constrained and Radially Stretched Elastomer.

Consisting of a stretchy silicone layer imbued with an inflexible fiber mesh in precise locations, the material can be inflated like a balloon into a predetermined 3-D shape. 

Pikul helped developed CCOARSE with colleagues at Cornell University, where he conducted work as a postdoctoral researcher under Itai Cohen, professor of physics, and Rob Shepherd, assistant professor in the Sibley School of Mechanical and Aerospace Engineering. The three are now patenting the technology.

Their inspiration came from cephalopods’ papillae, bumps that extend from the skin as the result of erector muscles below. The researchers developed CCOARSE to act as synthetic tissue groupings that mimic the papillae’s shape-changing behavior, producing bumps and bulges in varying shapes and sizes. A simple algorithm determines where fibers must be placed in the silicone sheet to achieve the desired final form.

Given the complexity of cephalopod’s camouflage system, Pikul envisions even finer-grained control over CCOARSE’s ultimate shape as being possible.

“Cephalopods have different subsets of papillae and activate them in different combinations depending on what surface texture they want to mimic,” said Pikul. “We could begin thinking about CCOARSE like pixels on a display. Each individual shape change would be relatively simple, but, combined, you could achieve complex results.”  

Eventual applications could include disappearing computer displays, virtual reality interfaces that give users touch feedback and medical devices, such as balloon catheters that take complex shapes when inflated. 

“We’re even thinking about more fun ways to use this technology, like in architecture and fashion,” Pikul said.

Pikul’s work on CCOARSE is part of his larger research interests in using soft matter to engineer new materials on multiple scales. Soft matter at the nanoscale can be used to make batteries that charge in seconds, or materials that increase the operating range of robots or vehicles by being lighter while also having a higher structural strength.

Soft materials could also be useful in developing soft robots that use elements of CCOARSE’s technology to change their shapes. Adding chemical and physical function to these stretchable materials that transform their surface texture would enable a wider range of applications for these robots.

The research was funded by the Army Research Office through Grant W911NF-16-1-0006 and the Air Force Office of Scientific Research through Grant FA9550-09-0346.

Also contributing to the study were Cornell graduate students Shuo Li and Lillia Bai. Roger T. Hanlon, senior scientist at the Marine Biological Laboratory in Woods Hole, Mass., provided guidance on replication of octopus skin.

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