Phosphorylated Zwitterionic Fluorinated Polyimide Membranes: Molecular Hydration Dominated Blood Contacting Bio‐Interface for Enhancing Antifouling, Anticoagulation, and Biocompatibility

Polyimide (PI) is recognized as a high‐performance biomaterial membrane due to its high mechanical strength, excellent biocompatibility, biological stability, and highly tunable chemical structure. However, the intrinsic hydrophobicity of PI blood fluid contact ultrafiltration (UF) membrane materials poses risks related to separation efficiency and stability, as well as complications arising from biofouling and immune cascades. In this study, benzimidazolium‐based phosphorylated zwitterionic PI (BI‐ZFPI‐Me/Et/ i ‐Pr) polymers were synthesized via polycondensation and phosphorylation using three different reagents (MeOEP, EtOEP, and i‐PrOEP). These polymers were then used to prepare intrinsic flat‐sheet blood‐contacting UF membranes via NIPS. All phosphorylated zwitterionic PI membranes not only exhibited reduced water contact angle (19.8°/17.0°/16.8°vs. 57.2°) but also demonstrated superior UF performance, with FRR values exceeding 93% and cycle stability far surpassing that of the pristine BI‐FPI membrane (76.9%). Among the three zwitterionic membranes, BI‐ZFPI‐Me, due to its optimal hydrophilic‐hydrophobic balance, showed excellent hemocompatibility—including a hemolysis rate < 0.5%, high plasma recalcification time (28 min), and anti‐complement activation—while BI‐ZFPI‐ i ‐Pr exhibited the best cell viability (93.3%), enhanced endothelial cell compatibility, and promoted M2 macrophage polarization. This study indicates that intrinsic zwitterionic phosphate polyimides show promising potential in biomaterial separation membranes due to excellent multifunctional biological anti‐fouling, anticoagulation, and biocompatibility.