Development and Characterization of a Stable Oil-in-Water Nanoemulsion Using Impingement Jet Mixing and Lyophilization Techniques

Nanoemulsion (NEM) is an effective adjuvant and delivery system for vaccines and nucleic acids, capable of inducing immune responses against diverse pathogens. Background/Objectives: Conventional NEM manufacture uses multi-step operations, typically high-shear homogenization and then microfluidization (HSHM), thereby increasing process complexity and contamination risk. As water-rich colloidal dispersions, NEM is prone to microbial proliferation and droplet coalescence; freezing further disrupts microstructure, causing phase fusion and separation, so NEM adjuvants are often stored separately from antigens in multi-vial formats. Lyophilization could reduce cold-chain dependence and enable single-vial products, but there is no systematic study on lyoprotectants comparation and process optimization of lyophilized NEM. Methods: An impingement jet mixing (IJM) process was evaluated as a simplified, scalable route for NEM production. Key IJM parameters, including flow ratio, total flow rate, preparation temperature, microchannel type, and shear mode—were examined to match attributes of conventional HSHM. Lyophilized and reconstituted NEM were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry and/or in vitro potency to inform lyoprotectant selection, and Taguchi Design of Experiment (DOE) methodology guided lyophilization processes. Results: IJM yielded NEM with droplet size, polydispersity index (PDI) and morphology comparable to HSHM, with higher throughput and fewer unit operations. Optimized lyophilization technique with designed lyoprotectant and process formed closed structures to prevent the easy-to-flow monolayer of the emulsion from fusing, producing robust and stable NEM. Conclusions: Coupling IJM with targeted lyophilization establishes a scalable, lower-risk manufacturing paradigm for NEM that preserves critical quality attributes, reduces cold-chain reliance and enables single-vial adjuvanted vaccine formats with tangible industrial and clinical benefits.