Designing cryogels through cryostructuring of β-chitin nanofibers to reinforce polyelectrolyte complexes for non-compressible hemorrhage control.

Non-compressible hemorrhage remains a major clinical challenge, requiring hemostatic materials with rapid blood absorption and sufficient mechanical robustness. Conventional carboxymethyl chitosan (CMCS)/sodium alginate (SA) polyelectrolyte complex (PEC) sponges exhibit high swelling capacity but limited uptake kinetics and mechanical strength. Here, β-chitin nanofibers (β-ChNFs) were incorporated into the CMCS/SA system to establish a freeze-thaw reinforcement strategy depended on β-ChNFs. Repeated freeze-thaw cycles had little effect on the storage modulus (G') of CMCS/SA alone, whereas G' progressively increased with the number of cycles in β-ChNF-containing systems. After six freeze-thaw cycles and electrostatic complexation, the resulting double-network sponges featured layered, stacked pore walls that conferred excellent shape recovery and fatigue resistance, together with rapid blood absorption and enhanced platelet-red blood cell adhesion, thereby accelerating blood clotting. The β-ChNF-dependent procoagulant enhancement was mainly associated with activation of the intrinsic coagulation pathway, and the sponges also exhibited favorable hemocompatibility and cytocompatibility. In a rat liver perforation model, the optimized sponge demonstrated significantly superior hemostatic performance compared with a commercial gelatin sponge, achieving a hemostasis time of 3.5 s and blood loss of 80 mg, underscoring its strong potential for controlling non-compressible hemorrhage.