Snake scales and butterfly wings are the inspiration for a new surface developed by a University engineering lab, which could advance camouflage and biomedical technology.

The surface was designed and constructed by Seok Kim, assistant professor in mechanical engineering, graduate students Zining Yang and Jun Kyu Park and a lab team of students.

Their research, “Magnetically Responsive Elastomer-Silicon Hybrid Surfaces for Fluid and Light Manipulation,” was recently published in Small, a peer-reviewed journal for nano and microscale technology. Yang, Kim and Park were all corresponding authors of the paper.

According to their paper, functionalities of the surface can be expanded by introducing other materials atop the scales, like bare silicon, black silicon and photonic crystal, in both vertical or horizontal scale positions. Micropillars are little, magnetically controlled pillars that react instantly to varied levels of magnetism and are able to return to their original position.

Kim said he wanted to emulate designs found in nature, such as snake skin or butterfly wings, where overall surface property looks soft and flexible, but is actually stronger than it looks.

“Nature has a very efficient way to create some functions, utilizing lesser amounts of resources and energies. That is why we would like to be inspired by nature,” Kim said.

Possible applications for the surface range anywhere from digital microfluidics to virtual blinds to camouflage.

Digital microfluidics is a technology that enables liquids to be controllably transported, merged and mixed without other stirrers, which would be helpful in biomedical or bioanalytical research. 

Virtual blinds are blinds that can be remotely controlled to block out light. Tunable optical transmission, the ability to control the transparency or opaqueness of something, could lend itself to inventions like virtual blinds. Magnetization could control the amount of light let into a room, Yang said.

Yang also said that when topped by photonic crystals, the skin becomes a surface able to manipulate light and change color. If the individual micropillars can be controlled, applications like camouflage or display could be possible.

The skin is constructed in three phases, Kim said. First, they make the soft skin containing many magnetic micropillars. Then, they construct scales out of a small, nanostructured silicon arrangement.

The two separate pieces are finally brought together through a transfer-printing-based microassembly technique, which Kim said is their lab’s specialty.

Yang said this microassembly technique allows their lab to do what others have not.

“I think people always want to make this kind of structure that comes from nature,” Yang said. “When we come in, we have this microassembly that makes it possible. Other people might want to do it, but their fabrication technique is not good enough to make it happen.”

Before they can reach a level where digital microfluidics or camouflage is possible, they have a few challenges to overcome. Individual motion, durability and cost are all obstacles they have left, Kim said.

Their lab has not yet created a sample in which individual micropillars can move separately. Although individual motion is a difficult challenge, Kim says they have a few ideas on how to accomplish this.

Their surface at this stage is very fragile, broken with a single wrong touch, so they will also have to find a way to make it more durable, he said.

Lastly, the skin is very expensive to produce. Kim said a single 2 cm by 2 cm sample costs around $100. If the skin is ever to be manufactured on a larger scale, costs would have to be brought down, he said.

Despite coming far from incubation and having many ideas on where to take the surface next, one thing still remains blank for Kim’s lab: a name for their invention.

“I’m not a native speaker, right, so it’s not my strength to come up with it,” said Yang. “I thought of something like ‘Mag-skin’ or ‘Mag-scale,’ because it is magnetically actuated scale. But that might not be a good idea.”

“‘Mag-skin’ or something,” said Kim. “Sounds great.”

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