Sea Urchins Inspire New Smart Materials

The research, published in the journal *Nature*, was led by Professor Lu Jian, Dean of the College of Engineering at City University of Hong Kong. His team discovered that the natural porous ceramic of sea urchin spines has an innate ability for mechanoelectrical perception. The team observed the long-spined sea urchin (*Diadema setosum*) and found that when a single drop of water landed on a spine, it would rotate rapidly in about a second. This stimulation was found to induce a transient potential of approximately 100 millivolts. This electrical response is incredibly fast, occurring within tens of milliseconds, which is over a thousand times faster than the sea urchin's own visual perception. Crucially, the spines produce this voltage even without any living tissue, proving the phenomenon is based on the material's physical structure. Electron microscopy revealed the spine's secret: a porous skeleton with a gradient of pore sizes. Smaller pores near the tip increase the surface area, which enhances charge separation at the solid-liquid interface as water moves through, generating a measurable voltage. Using a 3D printing technique called vat photopolymerization, the scientists fabricated a biomimetic replica of this gradient structure. The engineered material showed a threefold increase in voltage output and an eightfold increase in signal amplitude compared to structures without the gradient design. This breakthrough demonstrates that the material's topological structure, rather than its composition, is the key to its mechanoelectrical properties. The team has already built a prototype mechanoreceptor that can detect the intensity of underwater flows in real-time without needing an external power source. Potential applications for this new smart material are vast and include marine environmental monitoring, intelligent underwater exploration, and new platforms for integrated structural and functional materials in aerospace engineering and biomedical devices.