Bioinspired hierarchical materials for atmospheric water harvesting: a dual-track perspective of surface regulation and sorbent engineering.

The escalating global water scarcity poses an urgent demand for sustainable freshwater production technologies. Atmospheric water, representing over 12 900 billion tons, constitutes a ubiquitously distributed, abundantly available, and continuously renewable freshwater. Atmospheric water harvesting (AWH) has emerged as a promising technology due to its wide distribution and renewability. Numerous biological organisms offer a wealth of biological prototypes that serve as biomimetic templates for designing hierarchical structures in artificial water harvesting materials. This review systematically summarizes recent advances in bioinspired hierarchical structure design for AWH. We begin by establishing the fundamental theories of surface wettability and the thermodynamic/kinetic foundations of water vapor adsorption. Subsequently, we organize advanced AWH materials within two complementary, mechanism-based tracks: droplet management via surface regulation (DMSR) and sorbent-based atmospheric water harvesting (SAWH). Rather than merely separating technologies by water source or material family, this dual-track framework maps bioinspired hierarchical structures onto the dominant transport bottlenecks they address: interfacial droplet nucleation-transport-detachment in DMSR and intrasorbent vapor sorption-diffusion-regeneration in SAWH. It thereby provides a common basis for comparing how hierarchical design coordinates water capture, transport, and release across fog, dew, and vapor harvesting.