Characterization of Sterilizing-Grade Membranes/Prefilters and Application to mRNA-LNP Process Development

Sterile filtration is an essential step in the production of lipid nanoparticles (LNPs) used in mRNA vaccines and therapeutics. The overlap between the particle size of the LNPs (typically 50–200 nm) and the pore size of the sterilizing-grade membranes (rated at 0.2 µm) complicates the design and operation of the sterile filtration process. The objective of this study was to characterize the pore size distribution, fouling behavior, and capacity of different sterilizing-grade membranes and prefilters for LNP filtration. Mercury intrusion porosimetry revealed significant variability in pore size distributions across several sterilizing-grade membranes despite their consistent 0.2 µm rating, with LNP filtration capacity strongly correlated with the experimentally observed mean pore size. Dual-layer membranes, including the 0.8/0.2 µm Sartopore 2 XLG, significantly enhanced LNP filtration capacity and reduced fouling due to their integrated prefilter layer. Prefilter membranes with pore sizes in the 400–800 nm range provided the greatest enhancement in LNP filtration capacity. These findings highlight that for a given LNP formulation, the filtration capacity is strongly influenced by sterilizing-grade filter selection and specifically by the membrane pore size distribution and morphology, which are generally not published by filter manufacturers.