When Chang-Hwan Choi looks at the natural world, he sees potential. Choi, a professor in the Department of Mechanical Engineering at Stevens Institute of Technology, has devoted his career to studying nanoscale structures in nature—like miniscule projections on the surfaces of leaves and insect wings—and applying those ideas to improve human technology. “If you really see nature carefully, it’s fascinating,” he explained. “Nothing is just random or by accident.”
Inspired by nature
Choi’s interest in the surfaces found in nature began during his doctoral program. He studied aerospace engineering as an undergraduate and master’s student at Seoul National University before earning his doctorate at the University of California Los Angeles, where he worked on nanotechnology and micro-electromechanical systems (MEMS).
Choi’s doctoral advisor C.J. Kim was interested in how lotus leaves stay clean despite growing in muddy environments. It turns out those leaves are covered with micro and nanoscale structures that minimize contact between water and the surface of the leaf. This reduces a water droplet’s ability to adhere to the surface and reduces friction, so the water bead simply runs off the leaf. “[My PhD advisor] asked me to create a structure to mimic the lotus leaf and test if we could use the surface for reducing drag in liquid flow,” said Choi. “His interest was using this kind of structure for applications from small pipes to large vessels… I was fascinated by this, and then after I came to Stevens, I found there are many other examples and application potentials.”
Some notable examples include insect wings, whose nanoscale structures prevent the adhesion of contaminants, so a slight wind simply blows dirt and bacteria off. These structures can even kill the bacteria by poking their cell membrane. Another example is the way the surface of an insect’s eye inhibits water condensation and frosting so the eye remains clear in icy conditions. “I was pretty fascinated by this and wanted to understand how these tiny micro- and nanoscale structures change all these different functionalities,” said Choi. “That was my interest, and my expertise was micro/nano manufacturing—so I can fabricate similar nanoscale or microscale structures by using many different techniques.”
One of Choi’s current projects involves adding nanoscale structures to artificial corneas. These look a bit like a standard polymer contact lens, but if you zoom in, the surface is dotted with miniscule structures that—like an insect wing—prevent bacteria from adhering to the surface. Choi says these structures facilitate tissue cell growth but block the growth of bacteria, which can cause infection after a cornea transplant.
Choi has also fabricated surfaces for industrial applications, such as coatings that reduce corrosion, biofouling, and drag for submarines; coatings that reduce icing on airplanes; and antimicrobial surfaces that can resist microbial contamination during food processing and surgical procedures.
A powerful partnership
Choi accepted a faculty position at Stevens in 2007. He was drawn to the school because of its legacy in mechanical engineering—Stevens introduced the first mechanical engineering degree in the U.S. in 1870, and the American Society of Mechanical Engineers was founded at Stevens in 1880. He also liked the university’s broad-based interdisciplinary philosophy, emphasis on innovation and entrepreneurship, small class sizes, historic collaboration with the US Navy, and renowned marine research laboratory: The Davidson Lab.
Choi especially hoped to use those facilities to study how to reduce friction and drag on ships—but when he proposed the idea to the Navy, they asked if his work might prevent an even bigger problem: corrosion. Since the surfaces of deployed ships are in constant contact with saltwater, engineering surfaces that repel water could reduce the costs of maintenance and repair against corrosion.
Since then, Choi has received several research grants from the Navy, including a 2010 Young Investigator Program award from the US Office of Naval Research for his work on anti-corrosion surfaces.
Now, he’s expanding that research to incorporate brand new technology: 3D metal printing, also funded by the Navy. Choi is using that printer’s high-power laser to build new metal alloys layer by layer, selecting for anti-corrosive properties. Eventually, he hopes to incorporate surface nanostructures—perhaps as a coating or by taking advantage of pores that form in the alloys during 3D printing. In a separate project, Choi is also working on 3D printing alloys that can be used to build components for eco-friendly cars.
Always a teacher
Choi says he enjoys his research—especially when he comes up with an idea that works—but his primary priority is teaching. “My dream was to be a professor,” he said. “I like teaching and interacting with students.”
Choi loves that the small community at Stevens means he can build close relationships with faculty and students. He advises his students to follow his lead by asking good questions and being open-minded about where the research leads. He says breakthroughs come when you make connections between areas that haven’t been considered together before.
“Right now, if someone asked me, ‘What is your area of expertise?’ it would be hard for me to answer. In the past, micro/nano fabrication and fluid/thermal engineering were my areas of expertise, but right now [I’m working on] corrosion, biofouling, and metal 3D printing… I had little background knowledge in [materials science or biology], but I dared to study those things,” explained Choi. “So, my advice is no one should be afraid to learn new things and combine those new things with their area of expertise.”
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