Failure of sulfobetaine methacrylate as antifouling material for steam-sterilized membranes and a potential alternative

Abstract

This works reveals that copolymers containing sulfobetaine methacrylate (SBMA) units as antifouling agents fail at providing poly(vinylidene fluoride) (PVDF) membranes with antifouling properties after a steam sterilization procedure. Contrarywise, copolymers containing sulfobetaine methacrylamide (SBAA) units are unaffected by the steam sterilization. In other words, the antifouling properties of the coated membranes are comparable before or after steam sterilization. In this study, two copolymers containing styrene segments, ethylene glycol methacrylate segments and either SBMA or SBAA (PS-r-PEGMA-r-PSBMA and PS-r-PEGMA-r-PSBAA) were synthesized and coated on commercial hydrophobic membranes. After characterizing the membranes’ physicochemical properties and verifying that the sterilization had little effect on the coating stability, it was demonstrated that membranes coated with PS-r-PEGMA-r-PSBAA had comparable hydrophilic properties and antibiofouling properties (tested using Escherichia coli, fibrinogen, whole blood) before and after sterilization, while membranes coated with PS-r-PEGMA-r-PSBMA failed. Liquid chromatography and mass spectrometry (LCMS) analysis revealed that steam sterilization of SBMA monomers (279 g/mol) arose in the ester bond cleavage. Species of Mw 211 g/mol could be detected, alongside original SBMA species at 279 g/mol from the MS spectrum of the monomer. On the other hand, the structure of SBAA remained intact after the process. A similar observation was made with copolymers: while cleavage of PS-r-PEGMA-r-PSBMA to numerous fragments occurred, the analysis of PS-r-PEGMA-r-PSBAA did not provide evidence of the copolymer fragmentation in the detection range. Therefore, the results of this work provide solid evidence that it is preferable to use SBAA-derivatives to improve the fouling resistance of membranes if steam sterilization is needed (as in biomedical industry), rather than common SBMA.