In areas where we don’t want adhesion, we use a cone pattern.” Under the microscope, the students could see a bumpy surface consisting of tiny structures shaped like truncated cones. The topography allows water to slip off the wing and keep it clean. Ing and Liang proceeded to replicate the surface pattern on different polymers. When Ing moved on to work in another lab, Liang continued the research and developed techniques to reproduce the patterns with nanoimprinting. Finally, she tested the surface properties with bacteria, observing what kinds of patterns cause the bacteria to die or to adhere. She found cone patterns cause cell death while line patterns promote adhesion.
rejected or causing inflammation. But it has to remain clear,” Yee explains. His solution is to create an artificial cornea with a nanopatterned surface. His students’ work on the cicada wings demonstrates its feasibility. “In areas where adhesion is needed, we use a line pattern. In areas where we don’t want adhesion, we use a cone pattern,” he explains. Ing has also proposed that cicadainspired nanosurfaces could be used by NASA to tackle the problem of bacterial growth on the International Space Station.
In such a closed environment, bacteria can flourish, sickening astronauts and causing equipment failure. “But,” she says, “if the structure itself can kill bacteria without any chemicals, that would be ideal.” Both Ing and Liang say the cicada project has given them a new respect for nature and the field of biomimetics – the study of biological structures and systems as templates for engineering man-made goods. “We want to be able to replicate what we see in nature and find practical uses in the medical world and in research,” Liang says.
“Clearly these bacteria are able to sense their surroundings and change their shapes to conform to the surface they are in contact with,” Yee explains. Creating nanosurfaces with antibacterial properties is a highly sought-after goal in biomedical engineering. While chemicals – antibiotics – can be added to a surface, they often degrade over time or the bacteria become resistant to the drugs. Numerous medical devices could be improved if they could be designed with nonchemical antibacterial surfaces. For example, Yee is working on an artificial cornea, which is proving to be no simple feat. The product has to be made of a polymer that the body won’t reject and yet will resist the natural tendency of epithelial cells in the eye from growing over it. “There are these conflicting demands: It has to be incorporated into the eye without moving, being
“The cicada has a wing surface that has exactly the nanopatterns we’ve been working on. It was quite a fabulous serendipity.”
Samueli School of Engineering • UC Irvine
35