Earlier this year, physicists from the Université Paris-Saclay, Stanford, and Princeton announced a mathematics breakthrough in the study of granular jamming. They investigated this counterintuitive phenomenon by creating physical models out of materials such as sand and coffee grounds. This study is a big step forward, as it shows granular jamming occurring within a living organism for the first time. Those findings were recently published in the Proceedings of the National Academy of Sciences. They zoom in on the coral species Leptogorgia chilensis, which flourishes among the rocky outcroppings along the Pacific coast from California to Chile.
Lead researchers Ling Li and Chenhao Hu took a closer look at the coral’s skeleton. They found that its special granular particles – technically called sclerites – let the coral control its flexibility/stiffness. This “mechanical memory” once better understood could be applied to create exciting, new smart-engineering applications. It has tremendous promise in robotics and medical devices, where variable stiffness can enhance usability and capability.
Understanding Granular Jamming
Granular jamming describes what happens when a granular material, like rice or beans, gets stiff when you push down on it. So far, this phenomenon has primarily been explored with inanimate materials. The novel contribution of Li and Hu’s research is its application in biological settings. The team used advanced imaging methods to focus on and identify the sclerites found within the skeletons of Leptogorgia chilensis.
Sclerites are small calcareous units that contribute greatly to the physical structure of the coral. The coral’s tube-like structure offers some extraordinary properties. Its branching outgrowths form at periodic intervals, allowing the coral to vary its stiffness in response to applied forces. Under pressure, these sclerites interdigitate, jamming together and thus locking into place while adding to the skeleton’s rigidity.
“Once the sclerites get close enough to their neighbors, their branches jam together, holding them in place,” – Chenhao Hu.
Li and Hu found that when coral tissues excrete water due to mechanical or chemical stimulation, the jelly-like material shrinks. Their findings go a long way towards illuminating this amazing process. This movement brings the sclerites into closer apposition. In the process, their own jamming capacity is enhanced, bolstering the collective stiffness of the coral’s skeleton.
Implications for Engineering
The ramifications of this study reach far past the scope of marine biology. This unprecedented ability to programmatically vary material stiffness opens new frontiers across many engineering disciplines. Li expressed enthusiasm about the potential applications, stating, “There are so many situations where we might want to selectively tune the stiffness of a material.”
This research could inspire engineers to create more versatile robotic arms or surgical instruments that can adapt their rigidity based on specific tasks or conditions. Hu elaborated on this potential, saying, “Imagine being able to adjust the stiffness of a surgical instrument or robotic arm.”
All of the discoveries can help to propel new breakthroughs in material science. They open our eyes to how natural systems accomplish highly complex mechanical tasks. Li noted that nature has already provided a blueprint for engineers to explore further innovations: “In this coral, nature has given us a blueprint we can follow.”
A Broader Perspective on Coral Adaptability
Leptogorgia chilensis is a useful and accessible case study for scientists to explore. It barely touches on the profound diversity that one can find all tucked away within soft corals. Li observed that numerous other soft coral species incorporate various sclerite shapes. This diversity may lead to more complex mechanical properties.
“But there are many other soft coral species out there, which use different sclerite shapes, with potentially different properties,” – Ling Li.
Understanding these differences could yield additional insights into how various organisms adapt their structures for optimal performance in their environments. Hu emphasized that their work reveals impressive properties exclusive to this species. Beyond these discoveries, it opens up the door for further investigations of other soft corals and their unique adaptations.
Leptogorgia chilensis exhibits an impressive flexibility. From nature’s inspiration to human technology. This exploration of nature’s potential shows just a few of the ways it can be applied.