Directional Pore Size–Mediated Blood Hydrodynamics Govern Hemostasis in Cellulose Sponges

Abstract Uncontrolled bleeding remains a major clinical challenge in trauma and surgical care, requiring hemostatic materials that combine rapid blood absorption with efficient clot formation. However, the interplay between fluid dynamics and coagulation within porous architectures is still underexplored. Herein, a cellulose‐based hemostatic sponge featuring directionally aligned channels with tunable pore sizes is reported, enabling precise modulation of blood hydrodynamics at the wound interface. By integrating in vitro coagulation assays and in vivo hemostasis models, we reveal a strong dependence of clotting efficiency on channel size of directional channels. Sponges with an intermediate pore diameter (≈34.2 µm) of directional pores exhibit superior performance, characterized by rapid erythrocyte enrichment, accelerated fibrinogen depletion, and enhanced clot mechanical stability. Rheological analysis confirms that this optimal structure achieves a balanced absorption rate that maximizes local retention of coagulation components. This study establishes a structure–function design principle that leverages directional pore engineering to regulate blood–material interactions, offering a scalable strategy for next‐generation hemostatic biomaterials.