Effects of different mixing techniques on mRNA lipid nanoparticle physicochemistry and biological performance

Lipid nanoparticle (LNP) formulation requires a mixing step. Many studies, especially from academic groups, utilize microfluidic mixers or hand mixing to prepare LNPs, while commercial-scale processes use turbulent-flow mixers. This discrepancy in mixing techniques has been underexplored, as LNPs made by different techniques may exhibit different performance, meaning bench-scale results cannot be replicated using materials manufactured at scale. Here, we isolate and interrogate the effect of primary mixing on LNP formulation. LNPs are produced from ten mixers while holding all other formulation parameters constant, to directly compare across techniques. We show that LNPs produced from the different mixers exhibit widely different physical properties and biological performance. Notably, manual pipetting common in academic practice yields particles that do not resemble those produced by turbulent-flow mixers. Findings are connected mechanistically to physicochemical characteristics arising from different flow regimes. Further establishing the relationship between mixing and LNP properties is critical.