Sea Urchins Inspire New Smart Materials

The research, led by Professor Lu Jian at the City University of Hong Kong, was published in the journal *Nature* and reveals a previously unknown capability of sea urchin spines. The team discovered that the spine's natural porous ceramic structure can generate a measurable voltage signal from the movement of water over its surface. This response is remarkably fast, occurring within tens of milliseconds, which is over a thousand times faster than the sea urchin's own visual perception. Observations of the long-spined sea urchin, *Diadema setosum*, showed that a single drop of seawater landing on a spine's apex caused it to rotate in about one second. This droplet stimulation was found to induce a transient potential of approximately 100 millivolts. Crucially, the researchers confirmed that this electrical response is an intrinsic property of the material's microstructure, as it persists even without any living cellular tissue. The key to this phenomenon lies in the spine's internal structure, known as a stereom, which has a gradient of pore sizes along its length. As water flows through these microchannels, an electric double layer is formed at the solid-liquid interface, generating a streaming potential that is converted into a measurable voltage. This effectively allows the spine to act as a natural micro-sensor. Using vat photopolymerization 3D printing, the research team fabricated biomimetic polymer and ceramic samples that mimicked this gradient structure. Their artificial structures demonstrated a threefold increase in voltage output and an eightfold increase in signal amplitude compared to structures without the gradient design. This proves that the mechanoelectrical perception is primarily governed by the topological structure, not the specific material. This breakthrough challenges the conventional view that natural porous structures serve mainly mechanical functions. The discovery of their latent sensing capabilities opens new avenues for structure-function integrated material design. The resulting smart material can be used to create mechanoreceptors that can detect underwater flow direction and intensity in real-time without needing an external power source. Potential applications are vast, ranging from marine environmental monitoring and intelligent underwater exploration to biomedical devices and aerospace engineering.