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

The physics underlying these puzzling phenomena can be traced back to the microscopic interactions between the solid particles in the suspension. When these particles are under stress, they must rearrange themselves, a process that can lead to increased viscosity. At low stress conditions, particles can roll past one another relatively freely. However, as stress builds, the resulting forces can lead to scenarios where particle movement becomes hindered, requiring a much greater force to achieve the same flow, which results in that notable thickening effect.

The relationship between these microscopic interactions and the macroscopic properties of suspensions is a focus of ongoing research. A group of scientists from ETH Zurich, led by Lucio Isa, has recently developed a breakthrough measurement technique aimed at deciphering the frictional forces that influence particle interactions in these mixtures. Using an atomic force microscope, which allows for precise measurements on a microscopic scale, the researchers set out to quantify the frictional forces at play between individual particles that are only a few micrometers in diameter.

In a novel setup, a special holder was designed to capture a single spherical particle, allowing for the exploration of its interactions with similar particles when subjected to movement. The atomic force microscope facilitated the simulation of the dynamics involved when two particles traverse past each other. By carefully analyzing the measurements taken during these interactions, the team was able to derive invaluable insights into the forces that dictate the flow behavior of these particle-laden fluids.

Understanding these interactions is particularly complex, especially when examining particles as small as 12 micrometers, where conventional measurement techniques would falter. Simon Scherrer, a doctoral student involved in the study, engaged in meticulous development of the measurement setup, indicating that numerous iterations were required before achieving a functional design that could capture the subtle yet significant forces at play. This attention to detail is crucial, as even the slightest misalignment or miscalculation can lead to misleading results.

The research team discovered that the surface characteristics of the particles play a pivotal role in determining how they interact with one another. For instance, particles with smooth surfaces tended to glide past one another effortlessly, highlighting a distinct frictional behavior that contrasts sharply with the interactions of rough or sticky particles. When rough or sticky particles were pressed together, they acted like gearwheels, allowing for rolling motion that encountered considerably less resistance. This behavior is fundamental to understanding the dynamics of suspensions, as the interplay between these forces heavily influences viscosity and flow characteristics.

Equipped with the ability to measure both rolling and sliding friction, the researchers now hold valuable coefficients that can be integrated into computational models. These models will enable scientists and engineers to simulate suspensions with high particle concentrations, allowing for optimization of their flow characteristics—essential for their applications across various industries. For example, in the concrete industry, adjusting the flow of materials could lead to better mixing and application processes, ultimately improving product quality and efficiency.

Beyond construction materials, findings from this research can also significantly impact the field of microelectronics. Currently, manufacturers employ dense suspensions containing metallic or conductive particles for soldering components onto circuit boards. The flow behavior of these materials is critical; if excessive pressure is applied, the paste can unexpectedly thicken and obstruct the nozzles, leading to operational inefficiencies. Hence, having a granular understanding of particle interactions can lead to the development of more reliable manufacturing processes that minimize such risks.

As scientists continue to unravel the complexities of microscale interactions in suspensions, the prospect of engineering improved mixtures becomes increasingly tangible. The implications extend far beyond academia, touching sectors that directly impact daily life and global economies. The detailed knowledge regarding microscopic behaviors not only aids in developing more effective materials but also opens doors to innovative approaches in product formulation across a variety of industries.

This research offers a window into the mechanisms that underlie the essential functions of a multitude of materials we often take for granted. The intersections of physics, engineering, and material science converge in this work, pointing to a future where enhanced suspension performance becomes a cornerstone of industrial innovation. With continued exploration of these microscopic forces and their broader implications, the potential to refine everyday materials remains vast.

In closing, the investigation into the rolling and sliding interactions among single particles serves as a reminder of how intricate the world of material science truly is. With researchers like Lucio Isa and his team at ETH Zurich pushing the boundaries of knowledge, we stand on the precipice of a deeper understanding that could transform how we perceive and utilize the materials that shape our world.

Subject of Research: Frictional forces in particle suspensions
Article Title: Characterizing sliding and rolling contacts between single particles
News Publication Date: 6-Mar-2025
Web References: Proceedings of the National Academy of Sciences
References: Scherrer S, Ramakrishna SN, Niggel V, Hsu C-P, Style RW, Spencer ND, Isa, L. Characterizing sliding and rolling contacts between single particles, PNAS March 6, 2025 122 (10) e2411414122
Image Credits: Simon Scherrer / ETH Zurich

Keywords

Suspension, non-Newtonian fluids, particle interactions, friction, material science, industrial applications, atomic force microscope, viscosity, microelectronics