Modulating cell stiffness to improve macrophage antibacterial defense: Utilizing spermidine-functionalized black phosphorus nanosheets for periodontitis treatment

• Spermidine modification endows BPNS with immunomodulatory antibacterial effects. • Cell stiffness is a novel target for improving macrophage antibacterial activity. • BPNS@Spd modulates macrophage stiffness by reducing membrane cholesterol content. • Autophagy-driven cholesterol efflux contributes to the membrane cholesterol change. Periodontitis, a prevalent microbe-driven disease, is characterized by the progressive destruction of tooth-supporting tissues. Porphyromonas gingivalis ( P. gingivalis ), a keystone pathogen in chronic periodontitis, evades clearance by periodontal immune cells, leading to microbial dysbiosis and alveolar bone resorption. Effective treatment requires the elimination of periodontopathogens and restoration of alveolar bone. Macrophages serve as the primary defense against periodontal pathogens. Cell stiffness, an intrinsic mechanical property of macrophage, is closely linked to their motility, deformability, and phagocytic function, presenting a potential target for enhancing macrophage antibacterial activities. Black phosphorus nanosheets (BPNS), a novel two-dimensional material that degrades into nontoxic phosphate in physiological environments, offer distinct advantages in bone regeneration. In this study, BPNS was functionalized with spermidine (Spd), a natural polyamine with immunomodulatory effects, to improve periodontal infection control. In addition to preserving BPNS's osteogenic activity, BPNS@Spd further enhanced macrophage antibacterial function by targeting cell stiffness. Reduced cell stiffness enhanced macrophage deformability and membrane fluidity, facilitating more efficient phagocytosis and clearance of P. gingivalis . Mechanistically, BPNS@Spd modulated macrophage stiffness and function by decreasing membrane cholesterol content, in which autophagy-mediated cholesterol efflux plays a critical role. This work underscores the potential of modulating membrane cholesterol and cell stiffness to boost macrophage-mediated bacterial clearance, offering an innovative immunomodulatory approach for managing microbe-driven inflammatory diseases beyond periodontitis.