Along the rugged Pacific coastline stretching from California to Chile, a remarkable marine organism exhibits a mechanical response that seems almost supernatural. The soft coral Leptogorgia chilensis has the extraordinary ability to transition from flexibility to stiffness almost instantly when its delicate branches are touched. This biological marvel, reminiscent of a comic book hero stretching and unyielding against threats, has now been scientifically unraveled by engineers at the University of Pennsylvania. Their findings expose a natural process of granular jamming within the coral’s mineral skeleton, shedding light on a natural phenomenon that may revolutionize engineered materials.
The research, recently published in the Proceedings of the National Academy of Sciences, uncovers how Leptogorgia chilensis achieves such rapid stiffening through a composite structure formed by millions of microscopic mineral particles embedded in a gelatinous matrix. On mechanical stimulation, the coral’s tissues expel water, causing the gel to contract and compress the suspended particles closer together. This compression elevates particle interactions to a point where movement ceases abruptly, a physical state known as jamming. Associate Professor Ling Li emphasizes this dynamic transformation as analogous to a “traffic jam” at the microscopic scale, where particle motion is arrested, conferring rigidity to the otherwise flexible arms.
Granular jamming has been extensively studied in inert materials like sand, coffee grounds, or engineered grains where particle shape, friction, and packing density dictate mechanical behavior. However, the discovery of such a jamming mechanism in a living organism employing hard mineral components has not been documented before. This biological adaptation not only confers survival advantages to the coral but provides an intriguing blueprint for designing materials that can reversibly switch stiffness on demand. Such a concept carries tremendous potential in robotics, medical devices, and manufacturing systems where adaptability and precision control of mechanical properties are sought.
The skeleton particles known as sclerites found in Leptogorgia chilensis measure about a tenth of a millimeter and have a unique morphology—cylindrical rods sprouting numerous branched outgrowths spaced regularly along their length. This specialized geometry facilitates interlocking between adjacent particles, increasing frictional forces necessary for the system to jam securely under compression while allowing easy disengagement when relaxed. Through advanced imaging modalities and computational simulations, the research team characterized these shapes and verified their efficacy in creating a natural jamming system that outperforms more simplistic geometries often used in synthetic granulated materials.
Previous work in the field of soft robotics has explored granular jamming by filling flexible membranes with spherical or irregular grains that harden upon vacuum suction, enabling robotic “grippers” to adapt to complex objects. However, one significant limitation of such systems is the limited ability of spherical particles to interlock and resist shear forces, often leading to slippage or incomplete stiffness control. The branched sclerites of the coral provide inspiration by illustrating how nature has engineered particles that balance the need for stability and reversibility, a critical insight for next-generation adaptive materials.
The study involved meticulous physical manipulation tests on preserved coral samples, where researchers applied mechanical force to observe how the skeleton’s volume and stiffness changed dynamically. Measurements revealed that the coral skeleton initially shrinks in volume under pressure as particles move closer, leading to jamming, after which it behaves as a solid. This contrasts with other biological systems relying solely on elastic deformation. The unique feature here is the combined microstructure and gel matrix enabling a swift phase shift from soft to stiff states, a capability that has remained elusive in human-made materials.
This discovery not only advances the fundamental understanding of granular physics in biological contexts but also validates the notion that evolutionary processes select for particle geometries that optimize mechanical performance. Ling Li’s team suggests that other soft coral species with varied sclerite shapes may employ different jamming regimes to tailor their mechanical responses. The diversity of such natural microstructures represents a largely untapped resource for materials science seeking designs with tunable stiffness, durability, and responsiveness unattainable through conventional fabrication methods.
Transforming these biological principles into engineering innovations could herald a new era of devices that actively modulate their mechanical properties. Imagine surgical tools that remain pliable during navigation but stiffen precisely when required for cutting or suturing, or robotic appendages capable of adjusting their rigidity to handle fragile objects or perform heavy lifting within microenvironments. Additionally, manufacturing processes could benefit from granular jamming systems inspired by coral skeletons to selectively control form and finish without complex mechanical actuation.
One technical aspect underscored by this work is the fundamental importance of particle shape in jamming mechanics. The repeated branching structures found on the sclerites allow for high inter-particle friction and mechanical interlocking, critical for creating a jammed state robust to deformation. By contrast, naturally occurring granular materials with less specialized shapes, or engineered spherical grains, lack this capability. This finding supports a paradigm shift toward designing granular media where particle morphology directly encodes material function, moving beyond homogeneous, isotropic grain assemblies.
The study’s interdisciplinary nature spans materials science, mechanical engineering, marine biology, and physics, converging computational modeling with experimental microscale probing. The research was conducted collaboratively across institutions including the University of Pennsylvania, Virginia Tech, Brookhaven and Argonne National Laboratories, UCSB, Harvard, MIT, and the Zuse Institute Berlin. This extensive cooperation ensured comprehensive analysis from microscopic tomography to mechanical characterization, establishing a robust foundation for translating biological microstructures into synthetic materials science applications.
In conclusion, the gorgonian coral Leptogorgia chilensis exemplifies nature’s ingenuity in managing mechanical demands through a sophisticated mineralized skeletal system that exploits granular jamming at the microscale. This evolutionary innovation offers a renewable template for inventing materials and devices capable of on-demand stiffness tuning, potentially transforming medicine, robotics, and manufacturing. Ling Li and her colleagues’ foundational research illuminates how embracing complexity and morphology in granular media can overcome the limitations of traditional particle systems and unlock unprecedented functional capabilities.
Subject of Research: Animal tissue samples
Article Title: Mineralized sclerites in the gorgonian coral Leptogorgia chilensis as a natural jamming system
News Publication Date: 27-Oct-2025
Web References: http://dx.doi.org/10.1073/pnas.2504541122
Image Credits: Ling Li and Chenhao Hu
Keywords: Granular jamming, soft coral, Leptogorgia chilensis, mineral particles, sclerites, biomaterials, mechanical stiffness, adaptive materials, robotic grippers, calcium carbonate, bio-inspired engineering, particle morphology
