Degradable intrinsic zwitterionic polyimide ultrafiltration membranes with excellent antifouling performance and good biocompatibility

Abstract

Although having gained considerable attention in the field of membrane separation due to excellent thermal and mechanical properties and biocompatibility, fluorinated polyimides suffer from the inherent hydrophobicity that allows for the easy adsorption of hydrophobic organic and biological pollutants onto the membrane surface, leading to membrane fouling, reduced flux, and shortened service lifespan. In this study, carboxybetaine / sulfobetaine zwitterionic fluorinated polyimides (Py-ZFPI_1/2) and pristine Py-FPI membranes containing a phenyl-2-pyridine ether structure were synthesized and fabricated into ultrafiltration (UF) membranes by the NIPS approach. Smaller initial WCA values of zwitterionic membranes than pristine membranes (62.3° and 53.3° for Py-ZFPI₁ and Py-ZFPI₂ vs. 82.5° for Py-FPI) indicate high efficiency of zwitterionic side groups in improving the membrane hydrophilicity, which is attributed to the formation of a hydration layer induced by electrostatic interaction between zwitterions and water molecules. The intrinsic zwitterionic membranes show higher water flux than the pristine membrane (258.2 L/m²h and 280.5 L/m²h for Py-ZFPI₁ and Py-ZFPI₂ vs. 225.2 L/m²h for Py-FPI), accompanied by lower BSA adsorption (19.2 μg/cm² and 11.6 μg/cm² for Py-ZFPI₁ and Py-ZFPI₂ vs. 81.8 μg/cm² for Py-FPI). Zwitterionic membranes largely reduce bacterial and platelet adhesion by over 90 % and achieve the flux recovery rate of over 95 % after three cycles. Crucially, the phenyl-2-pyridine ether structure enables full degradation of all three membranes in a hydrazine hydrate medium in 6 days. This research indicates that degradable zwitterionic fluorinated PIs, particularly the sulfobetaine type Py-ZFPI₂, hold significant promise for applications in blood purification and biomedical separation.