Innovation through Bio-inspired Metamaterials
By Liz Sheeley
Professor Xin Zhang (ME, ECE, BME, MSE) is known for her pioneering work in building metamaterials, artificially designed materials that have properties not found in nature. Now, Aobo Li, a doctoral student in Zhang’s lab, has flipped that idea around to study the properties and functions of a natural material to improve on metamaterial designs.
Li chose to study a type of unicellular algae called diatoms. Their cell walls, called frustules, are made of silica and are hard like a shell. Depending on the species, these shells vary in shape, size and other physical characteristics. In work published in Small and Advanced Functional Materials, both as cover images, Zhang, Li and collaborators studied a particular diatom’s structure, used it as a scaffold to grow nanowires and, most recently, mimicked its structural pattern when making their own metamaterials.
“A lot of researchers find inspiration in their daily lives, sometimes it’s a random occurrence or thought that connects two ideas together, or sometimes it’s more purposeful and they choose to study a phenomenon they become curious about,” says Zhang. “In my field, that typically isn’t the case, but Aobo has shown how we can expand our inspiration and draw from natural elements and perhaps innovate in ways we couldn’t before.”
As an engineer, Zhang is used to building for a purpose, maybe to fill a gap in current technology. Li has brought science into the lab; he has sought answers for the sake of curiosity and then turned those answers into specific purposes.
After understanding the diatom’s properties and how its structure was unique, they chose to mimic those properties in making the completely artificial metamaterial. The frustule they were using as inspiration has a hierarchical pattern of hexagonally spread pores; each pore is inside a group of hexagonally arranged pores, as the pores get smaller and smaller. The original frustule looks like a honeycomb, an intricate, repeating pattern of tiny holes arranged in a hexagonal pattern even as they get smaller.
Other researchers have attempted to make metamaterials with hexagonally arranged pores, but instead of arranging those hexagons in hexagons, they arranged them in lines. Preserving the hierarchical pattern in a metamaterial gave Zhang and Li a metamaterial with new properties and the potential to create broadband infrared absorbers. Although this offers a practical application, the biggest takeaway from their research investigating why this new metamaterial is such a good infrared absorber—and that comes back to the bio-inspired hierarchical patterns of the pores in the metamaterial.