Researchers Create Smart Material from Sea Urchin Spines

The research, led by Professor Lu Jian, Dean of the College of Engineering at City University of Hong Kong, was published in the journal *Nature*. The team's work was inspired by the long-spined sea urchin (*Diadema setosum*) and its ability to quickly sense changes in its environment. They discovered that the spine's natural porous structure generates a measurable voltage when disturbed by water droplets or flow, a response that is over a thousand times faster than the creature's own visual perception. This electrical response is not biological but is an intrinsic property of the spine's physical makeup. The key is its gradient cellular structure, where the pore sizes change from the base to the tip. This variation in porosity, when interacting with flowing water, creates an electrical signal known as a streaming potential, effectively turning the spine into a natural micro-sensor. Sea urchin spines are a marvel of natural engineering, known for being strong, lightweight, and stiff despite being made of brittle calcite. Each spine behaves like a single crystal, with all its atoms aligned from one end to the other, a unique characteristic for such an elaborate and non-symmetrical shape. This intricate internal microstructure is what gives the spine its remarkable mechanical properties. Using an advanced 3D printing technique called vat photopolymerization, the researchers were able to replicate this complex, porous, and gradient structure in both ceramic and polymer materials. Their artificial designs demonstrated a threefold increase in voltage output and an eightfold increase in signal amplitude compared to similar structures without the gradient porosity, proving the design's effectiveness. The breakthrough opens up new possibilities for self-powered underwater monitoring and next-generation smart sensors. The team has already constructed a prototype mechanoreceptor that can detect the intensity of underwater flow in real-time without needing an external power source. This biomimetic approach could be foundational for a new class of integrated materials that have both structural and sensory functions. Potential applications are widespread, ranging from marine environmental monitoring and intelligent underwater exploration to water resource management and even aerospace engineering.