Bold claim: Sea urchin spines are not just for defense—they’re natural precision sensors, unlocking a new era of biomimetic technology. And this is where it gets controversial: structure may trump material choice in how we sense the world. A research team led by Prof. WANG Zuankai of The Hong Kong Polytechnic University (PolyU)—along with collaborators from City University of Hong Kong (CityU) and Huazhong University of Science and Technology (HUST)—has uncovered a mechanoelectrical sensing mechanism in sea urchin spines that stems from their gradient porous architecture. By mirroring this design with 3D-printed materials, they created a bionic metamaterial sensor with exciting potential for deep-sea monitoring, underwater infrastructure management, and even connections to brain-computer interfaces and aerospace technology.
In their study of the long-spined sea urchin (Diadema setosum), the team observed a rapid spine rotation within one second when a seawater droplet strikes the tip. Electrical measurements show that simulating a droplet interaction generates about 100 millivolts inside the spine, while actual water flow stimulation yields voltages in the tens of millivolts range. Notably, this mechanoelectrical response persists even in desiccated spines, indicating a mechanism independent of living cells and purely rooted in the spine’s physical structure.
The origin lies in the stereom structure—the porous internal skeleton made of pores with varying sizes. The pores display a clear gradient along the spine from base to tip: larger pores and lower solid density at the base, tapering to smaller pores and higher solid density at the tip. This bicontinuous gradient porous arrangement intensifies solid–liquid interactions as water moves through, causing shear forces at the electric double layer. These forces drive charge separation and redistribution, producing a measurable voltage difference. The gradient strengthens the coupling between fluid flow and pore surfaces, boosting both the magnitude and fidelity of the signal.
Guided by these insights, the researchers used vat photopolymerisation 3D printing to fabricate artificial samples that mimic the spine’s stereom. Tests show that gradient designs generate roughly three times higher voltage output and about eight times larger signal amplitude under water-flow conditions compared with non-gradient counterparts. This demonstrates that the sensory power mainly comes from the architectural design, not the material alone. Building on this, they created a 3D metamaterial mechanoreceptor arranged in a 3×3 array, with each unit composed of gradient-porous material. This device can record real-time electrical signals underwater and pinpoint the exact contact location of water flow without external power.
The team emphasizes that the gradient porous architecture enhances signal transmission, increasing the precision and sensitivity of the mechanoreceptor. By transferring this design to different materials, the approach could extend beyond water-flow sensing to detect various signals such as pressure, vibration, and electromagnetic waves. The implications are broad, including potential applications in brain-computer interfaces where improved sensing of neural activity could be transformative, as well as in aerospace and other advanced fields.
Prof. Wang summarized the advantages: compared with traditional mechanoreceptors, their gradient-porous design offers better manufacturability, flexible geometry, versatile materials, precise control over structure and performance, and real-time underwater self-sensing. By leveraging graded porous materials and 3D printing, the team envisions a new class of nature-inspired metamaterial sensors made from a range of materials, pore sizes, and surface features to support numerous applications.
Wang’s group is at the forefront of nature-inspired science and engineering and has already pioneered other biomimetic materials, such as lotus-leaf-inspired self-cleaning surfaces, Araucaria-leaf-inspired self-propelled liquid transport, and anti-icing structures that eject freezing droplets by mimicking spore-shooting in fungi. He believes these explorations will open fresh pathways for nature-inspired materials research.
As he notes, natural porous materials often owe their mechanical attributes to complex biomineralisation rather than being built primarily for strength. Revealing undiscovered mechanisms beyond a material’s traditional roles helps us understand and utilize these natural resources more fully, which is essential for advancing biomimetic research.
The study was co-led by Prof. LU Jian of CityU and Prof. YAN Chunze and Prof. SU Bin of HUST, with findings published in Nature. If you’d like to explore the full article, you can read it here: https://www.nature.com/articles/s41586-026-10164-9.
Consider this: what if gradient-porous design becomes the standard for underwater sensing and beyond? Do you think this approach could reshape how we design sensors for loud environments, space exploration, or even neuroscience? Share your thoughts in the comments about where you’d like to see gradient-porous biosensors applied next.
