Shape-shifting coral that stiffens in seconds to transform robotics

Researchers at the University of Pennsylvania have discovered that the Pacific soft coral Leptogorgia chilensis can rapidly shift its skeleton from soft to stiff by employing a natural granular jamming mechanism. This coral’s skeleton is composed of millions of uniquely shaped calcium carbonate particles called sclerites, suspended in a gelatinous matrix. When the coral is disturbed, it expels water, causing the gel to shrink and the sclerites to compact and interlock, instantly stiffening the coral’s branches. This biological example of granular jamming—previously observed only in non-living materials like sand—demonstrates a novel natural adaptation where hard mineral particles jam together to provide protection. The study, led by doctoral student Chenhao Hu and associate professor Ling Li, used advanced imaging, computer modeling, and mechanical testing to analyze how the coral’s sclerites interlock under pressure. The distinctive rod-like shape of the sclerites with branching outgrowths allows them to jam tightly when compressed, enabling the