Author: Zhu Hum Hum
Editor: Wang Haha
Typography: Li Xuewei
For the industrial sector, especially the automotive and aerospace manufacturing industry, it is necessary to find lightweight and robust materials. These new materials can improve energy efficiency while maintaining strength. However, in long-term industrial practice, the development of lightweight and high-strength materials has been unusually slow. After all, stronger materials tend to be denser and heavier.
Recently, Dr. Ling Li, an assistant professor from Virginia Tech's School of Mechanical Engineering, led a research team to point out the direction for the development of new lightweight and high-strength ceramic composites.
Dr. Ling Li's research team, through studying samples of multi-segmented starfish bones widely distributed in the Indo-Pacific region, found for the first time that the bones of starfish are made up of a single microlattice structure that is so uniform that it can be described mathematically and is composed of node-connected branches, similar to the structure of the Eiffel Tower. More interestingly, they also found that the uniform nature of the microlattice structure is a single crystal structure at the atomic level.
In this regard, Dr. Li said, "This unique material is like a lattice carved from a single piece of calcite, a near-perfect microlattice structure that has never been reported or synthesized in nature before." Most highly regular lattice materials are made by combining materials and small crystals to form composites, and this new microlattice structure is grown as a whole. ”
Figure | Science cover (Source: Science)
The study, titled "A damage-tolerant, dual-scale, single-crystalline microlattice in the knobby starfish, Protoreaster nodosus," was published on the cover of the latest issue of the journal Science.
How to achieve a balance between the quality and strength of industrial materials
We all know that materials with high density tend to be stronger and the corresponding weight is greater. For a simple example, a solid iron ball will obviously have a higher strength than a hollow iron ball. Therefore, for a long time, it has been difficult for industry to achieve a balance of quality and strength when designing new lightweight and high-strength materials.
In contrast, after millions of years of evolution, nature has come up with an ingenious solution to this problem, and that is porous materials, which produce extremely light and high-strength materials through the introduction of internal pores. For example, our bones, the roots of plants, and the hives of bees.
Figure | Hive (Source: Pixabay)
If we put these materials under a microscope, we will find that they are filled with tiny voids, as well as complex geometric structures. It is these complex pores that allow us to walk briskly and run briskly and withstand high-intensity shocks.
Therefore, for a long time, many materials workers have tried to draw inspiration from nature and open up new porous materials, especially new porous ceramic materials.
Compared with metal and polymer materials, ceramics have good mechanical properties, thermal properties and electrochemical properties can better withstand high temperatures and corrosive environments, but their brittleness often makes them easy to break, which greatly limits the wide application of ceramic materials.
Development of new porous ceramic materials inspired by nature
Previously, Dr. Li's team had found in cuttlefish bone that its unique porous bioceramic structure was both robust, fracture-resistant, and able to be used for buoyancy regulation. This project, as well as other studies like this, inspired Dr. Li to study the application of porous structures in nature at the microscopic scale.
In this work, Dr. Li and his team set their sights on the skeleton of a multi-segment starfish. In the past, we often saw starfish lying flat in various lazy positions on TV, so many people's first impression is that starfish is a very soft animal.
Figure | Starfish (Source: Pixabay)
In reality, however, as an echinoderm, starfish has an endoskeleton formed by the mesoderm, and various forms of small bone pieces are connected by connective tissue to form a whole, although the mass is very light, but the strength is very large, as tough as body armor.
Obviously, the high strength and toughness exhibited by starfish bones is an ideal material, revealing its principles to help make stronger, more durable porous ceramic materials.
To this end, Dr. Li led a research team to observe these starfish bone samples in the nanoscale characterization and fabrication laboratory, and found that on the microscopic scale, the lattice structure of the starfish skeleton was very regular, which was completely different from the porous structure of the previous cuttlefish bone and sea urchin spine. Rather, it is the most regular structure of the bones of invertebrates found so far, and this regular structure is very similar to the spatial frame structure commonly used in modern human architectural projects.
(Source: Virginia Tech)
Subsequently, the researchers began to explore how this natural lattice material has such a high mechanical strength, after all, the main components of starfish bones and chalk are calcite, obviously the strength of chalk is much lower than that of starfish.
However, the findings far exceeded Dr. Li's expectations. They found that each small piece of bone in the starfish's body consisted of a separate microlattice structure that was very uniform, connecting the branches through nodes, similar to the architectural structure of the Eiffel Tower. More interestingly, the team found that the uniform structure of this microlattice is essentially a single crystal structure at the atomic level.
This structure allows starfish to strategically strengthen the bones in a specific direction, providing enhanced protection. In addition, the animal seems to be able to thicken the tentacles along selected directions and specific areas, thus improving mechanical properties. Similar to the human body can adapt to the ability of the body to move by changing the local geometry of the porous bones.
In response, Patricia Dove, an expert in biomineralization and distinguished professor at Virginia Tech, said, "Starfish and other echinoderms living in highly predatory benthic environments are revealing a new world of materials that can guide the formation of extraordinary bones with only seawater and some organic components." This work is of great significance for the design of new materials in the field of mechanical engineering. ”
Dr. Li and his collaborators are currently experimenting with 3D printing technology to model and generate these complex lattice structures. While the 3D printed model currently created by the Li team is visually comparable, it will still take a while to bring this new, powerful ceramic architecture to market.
Figure | Dr. Li presents starfish skeletons and 3D printed models (Credit: Alex Parrish for Virginia Tech)
Currently, while 3D printers can produce microstructures, the process of eventual firing of printed ceramic products may introduce many uncontrolled tiny pores and cracks. These subtle changes can destroy its mechanical properties and become very fragile. In the future, with the advancement of 3D printing technology and the understanding of the mechanism of formation of starfish bone biological structure, new solutions may be provided.
Overall, this study reveals the secrets of starfish's high-strength bones at the nano level, pointing the way for the development of stronger, lighter porous ceramic materials in the future. In response, Dr. Li said, "Nature can assemble this complex biological structure under room temperature and environmental pressure, which is currently not possible with modern human technology." ”
Resources:
https://www.science.org/doi/10.1126/science.abj9472
https://vtx.vt.edu/articles/2022/02/eng-ling-li-starfish-skeleton.html
https://www.eurekalert.org/news-releases/942484?