New 'Smart Materials' Developed
A research team at City University of Hong Kong has developed a new class of 3D-printed smart materials. Inspired by the structure of sea urchin spines, the biomimetic "mechanoelectrical" materials could have applications in advanced sensors, medical devices, and sonar technology.
The research, led by Professor Lu Jian, Dean of the College of Engineering at CityU, was significant enough to be published in the prestigious scientific journal *Nature*. The study reveals that the natural porous ceramic structure of a sea urchin's spine can generate measurable voltage signals when water droplets or flows pass over it. This electrical response is remarkably fast, occurring within tens of milliseconds—over a thousand times faster than the sea urchin's own visual perception. The long-spined sea urchin (*Diadema setosum*) was a focus of the study, which found that a single droplet of seawater could induce a transient potential of about 100 mV. This electrical generation is not a biological process requiring living cells or nerves; it's an intrinsic property of the spine's physical microstructure. The key is the spine's stereom, a porous skeleton with a gradient of pore sizes that enhances the solid-liquid charge separation when water moves through its microchannels. Sea urchin spines are a marvel of natural material design, primarily composed of calcium carbonate, the same substance as chalk, yet they are incredibly tough and fracture-resistant. Their structure consists of highly oriented nanocrystals of calcite embedded in a "mortar" of amorphous lime and proteins. This composite structure, with its numerous internal cavities, makes the spines both lightweight and strong, able to distribute mechanical loads and prevent catastrophic failure. To replicate this natural wonder, the CityU team utilized a 3D printing technique called vat photopolymerization. By mimicking the gradient pore-size structure of the natural spines, their 3D-printed versions showed a threefold increase in voltage output and an eightfold increase in signal amplitude compared to structures without the gradient design. This confirmed that the unique sensing ability is governed by the material's architecture rather than its specific composition. The resulting "mechanoelectrical" material can detect underwater flow direction and intensity in real-time without needing an external power source or sensors. This breakthrough opens up new possibilities for next-generation smart materials with integrated structural and functional capabilities. Potential applications are vast, spanning marine monitoring, underwater exploration, aerospace engineering, and innovative water management systems.
