Sea urchins may be key to developing lightweight engineered cellular materials 

In the ongoing search for strong, lightweight materials, researchers are looking at sea urchins, which have spines made of chalk, and are generally brittle. Ironically, the highly complex three-dimensional structure of sea urchin spines is 70 to 80 percent porous and thus creates an overall stable, strong structure.

Studying the sea urchin is part of a $540,000 National Science Foundation grant being investigated by Ling Li, assistant professor of mechanical engineering in the College of Engineering. Overall, the research seeks to develop methods for acquiring, handling, processing, extracting, and evaluating the computational data for a hierarchical structure in order to integrate the information with 3D data and testing to develop engineered cellular materials.

By using design rules gathered from studying biological systems and inputting the rules into the design of bio-inspired lightweight ceramic materials, Li hopes the information can be applied to creating lightweight panels and other components for a variety of industrial purposes.

“I can see this information being applicable to panels, structural support, and armor to provide impact and blast protection,” said Li. “The design is very damage-tolerant and does not fail catastrophically.”

As the current work constitutes fundamental research to uncover the design principles of a biological material system, Li and his research team could only look forward at the potential for applying the lessons learned for innovative bio-inspired materials.

“We want to understand how nature designs lightweight materials with brittle components and we are trying to understand the 3D architecture of the sea urchin spine’s structure to see if we can determine how the structure helps achieve high strength and damage tolerance given the inherent weakness of the chalk it’s made from,” said Li.

Working with co-investigator Yunhui Zhu, an assistant professor with the Bradley Department of Electrical and Computer Engineering, the team will use a synchrotron tomography technique and mathematical tools developed by the Argonne National Laboratory to obtain high-resolution 3D volumetric data to determine how the porous network is designed in terms of connections, arrangements, and orientation.

“The project is based on characterizing and understanding the internal structure of the sea urchin spine to find out why it’s so strong,” Li said. “Sea urchin spines have been shown to perform similarly to the best ceramic cellular materials people have made in the lab in terms of relative strength.”

One of the differences between man-made and natural cellular structures is the nonsymmetrical formation of cellular struts and nodes, which also vary in thickness and orientation gradually at different locations.

“Most of our current 3D printed materials are based on idealized geometries, such as cylindrical beams with a constant cross-sectional area, which may contribute to catastrophic failure behavior in some printed ceramic solids,” Li said. “Looking at sea urchins, we see curved morphologies in stark contrast to 3D printed structures. By studying these, we hope to learn how to input these natural designs into our laboratory-created materials.”