Researchers Create 'Smart' Material from Sea Urchins
A research team at City University of Hong Kong has developed a 3D-printed smart material inspired by the porous structure of sea urchin spines. The biomimetic "mechanoelectrical" material has potential applications in sensors, robotics, and medical devices.
The unique sensing ability of the sea urchin spine is not biological but physical, stemming from its porous internal structure known as the stereom. This intricate, bicontinuous ceramic skeleton has a gradient of pore sizes along its length, with smaller and more numerous pores near the tip. This specific architecture is the key to its newly discovered mechanoelectrical properties. The material operates on the principle of "streaming potential." When water flows through the spine's microchannels, a charge separation occurs at the solid-liquid interface, creating a measurable voltage. A single droplet landing on the long-spined sea urchin (*Diadema setosum*) can induce a transient potential of about 100 millivolts, a response that occurs in tens of milliseconds—over a thousand times faster than the creature's own visual perception. Led by Professor Lu Jian, Dean of the College of Engineering at CityUHK, the research team includes Annan Chen, Ziqin Wang, and Zuankai Wang, among others, with their findings published in the journal *Nature*. The team successfully replicated the spine's complex gradient structure using a 3D printing technique called vat photopolymerization, which uses light to selectively cure a liquid ceramic-loaded resin layer by layer. A significant challenge in this process is precisely controlling the curing of the ceramic slurry to create the continuous gradient in porosity, which is essential for the material's function. Issues such as light scattering and managing the viscosity of the ceramic-rich resin must be overcome to fabricate the intricate, defect-free structures that mimic nature. The 3D-printed replicas outperformed their natural counterparts, exhibiting a threefold increase in voltage output and an eightfold greater signal amplitude compared to non-gradient structures. This demonstrates that the sensing capability is determined by the material's architecture rather than its chemical composition, opening the door to using various materials like polymers. This technology paves the way for a new class of self-powered underwater sensors. Potential applications include creating sensitive "skins" for underwater robots to detect subtle changes in water flow and vibrations, or deploying networks of battery-free sensors for long-term marine environmental monitoring.
