Interfacial stability and cross-scale design of bioinspired drag-reducing surfaces.

Surface free energy regulation and interfacial stability are central to drag reduction on bioinspired surfaces, with implications for antifouling in marine systems and flow management in blood-contacting biomedical devices. However, single-mechanism surfaces often operate within narrow windows and lose function under complex flow, pressure and fouling conditions. This review examines three representative classes of bioinspired drag-reducing surfaces, namely superhydrophobic coatings, riblet structures and compliant walls, with emphasis on their governing mechanisms, coupling pathways and failure modes. We discuss how interfacial slip, wetting-state stability, near-wall turbulence regulation and fluid-structure interaction act individually and in combination to alter wall shear stress, contact-line dynamics, energy dissipation and biological adhesion. Hybrid strategies, including superhydrophobic-riblet, superhydrophobic-compliant and multiscale integrated architectures, are considered in terms of both performance enhancement and engineering trade-offs. The major challenges are the absence of unified evaluation metrics, limited validation under realistic service conditions, insufficient long-term durability data and the difficulty of scalable fabrication. We argue that multi-mechanism drag reduction should move from peak-performance optimization toward durable biointerface design, in which hydrodynamic resistance, wetting stability, antifouling behavior and manufacturability are evaluated together.