One-step fabrication of antithrombotic coating via salt-gradient-driven liquid–liquid phase separation

Surface-induced thrombosis restricts the clinical safety of blood-contacting devices. Although surface heparinization is a widely commercialized strategy for enhancing hemocompatibility, current methods (e.g., covalent grafting, Layer-by-Layer assembly) suffer from complex procedures or insufficient stability. Herein, we introduce a facile, one-step strategy to construct robust anticoagulant coatings driven by a salt-concentration gradient. By utilizing 4 mol/L NaCl to screen electrostatic interactions between polyethyleneimine (PEI) and heparin, a homogeneous precursor slurry was prepared. During a simple immersion-withdrawal process, rapid salt diffusion at the interface triggers immediate liquid–liquid phase separation, inducing the dense coacervation of polyelectrolyte complexes onto substrates. The resulting coating exhibits exceptional stability via physical entanglement, retaining 73% of heparin after 16 days of physiological incubation. Furthermore, the coating demonstrated a negligible hemolysis rate (0.32%), suppressed platelet adhesion by 98%, and reduced ex vivo thrombus formation by 90%. This scalable assembly paradigm offers a highly effective solution for cardiovascular implant functionalization.