Echinoderm stereom gradient structures enable mechanoelectrical perception

Cellular solids ubiquitously exist in natural systems and are crucial for living organisms1,2. Their unique smooth branch and node morphologies are often seen as adaptations for enhanced mechanical performance3,4. Exploring alternative evolutionary functions can enrich the understanding of cellular solids, but it is frequently neglected. Here we show that the biomineralized cellular solids in echinoderm stereom (for example, sea urchin spine) have unexpected mechanoelectrical perception with response potential and response time, both of which are one to three orders of magnitude greater than those of echinoderm vision5. This exceptional perception originates from the gradient cellular solids (with varying void- or solid-phase diameters) along the [001] spine axis, generating a differential charge density across the stereom surface during liquid flow. Inspired by this natural wisdom, we create artificial spine-like structures using three-dimensional printing technology that exhibit three-fold higher voltage output and eight-fold greater amplitude differential than gradient-free samples, as well as a nature-inspired metamaterial mechanoreceptor capable of time-resolved self-monitoring information underwater. Our findings advance the understanding of load-sensitive biomimetic cellular solids (such as wood, sponge and trabecular bone), with the potential to develop functional gradient cellular materials towards underwater spatiotemporal sensing and water resource utilization. Sea urchin spines show exceptional mechanoelectrical sensing from gradient structures and can be replicated in 3D-printed mimics for underwater sensing.