The scientists discovered that the coral's skeleton contains millions of mineral particles suspended in a gelatinous matrix. When threatened, the coral expels water from its tissues, causing the gel to contract, drawing the mineral particles closer together. This process compacts the particles, which then jam together and stiffen the coral's structure.
Lead researcher Ling Li explained, "It's almost like a traffic jam. When stimulated, the coral's tissues expel water, shrinking the gel and squeezing the particles closer together until they jam in place."
This phenomenon, known as granular jamming, has been studied in non-living systems such as sand and coffee grounds, but this is the first documentation of the process occurring with hard particles in a living organism. The findings could inform development of new engineering materials capable of changing stiffness on demand, with potential applications in robotics, manufacturing, and medical devices.
First author Chenhao Hu noted, "In this coral's skeleton, nature has created an incredible material whose principles we can adapt for human use."
By examining the coral's skeleton at the microscale, the team found that the particles, or sclerites, are cylindrical rods with branching outgrowths. When the sclerites are packed together, their branches interlock and jam, allowing the coral to stiffen quickly and revert to flexibility once the stimulus is gone.
The research builds on years of work studying the structure and properties of marine organisms to unlock design principles for bio-inspired engineering. The team used advanced imaging and computational modeling to analyze the mechanics and structural organization of the skeleton.
Ling Li said, "We just studied one coral species. But there are many other soft coral species out there, which use different sclerite shapes, with potentially different properties." Future research may investigate the diversity of skeleton structures in related species to further inform new material design.
The research was supported by the Human Frontier Science Program, Penn Engineering, Virginia Tech, and the U.S. Department of Energy, with contributions from multiple institutions including Brookhaven National Laboratory, Argonne National Laboratory, UCSB, Harvard, MIT, and the Zuse Institute Berlin.
Research Report:Mineralized sclerites in the gorgonian coral Leptogorgia chilensis as a natural jamming system
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