Microfluidic Optimization of PEI-Lipid Hybrid Nanoparticles for Efficient DNA Delivery and Transgene Expression

<b>Background</b>: Lipid nanoparticles (LNPs) and polyethyleneimine (PEI) have independently been used for DNA complexation and delivery. However, non-ideal gene delivery efficiency and toxicity have hindered their clinical translation. We developed DNA-PEI-LNPs as a strategy to overcome these limitations and enhance DNA delivery and transgene expression. <b>Methods</b>: Three microfluidic mixing protocols were evaluated: (i) LNPs without PEI, (ii) a single-step process incorporating PEI in the organic phase, and (iii) a two-step process with DNA pre-complexed with PEI before LNP incorporation. The influence of DNA/PEI ratios (1:1, 1:2, 1:3) and DNA/lipid ratios (1:10, 1:40) on particle properties and delivery efficiency was examined. <b>Results</b>: In luciferase formulations, higher DNA/lipid ratios (1:40) produced smaller particles (136 nm vs. 188 nm) with improved cellular uptake (77% vs. 50%). The two-step method with higher DNA/PEI ratios improved transfection efficiency, with LNP-Luc/PEI 1:3 (40) achieving ~1.9 × 10⁶ relative light units (RLU) in luciferase expression. In green fluorescent protein (GFP) studies, LNP-GFP/PEI 1:3 (40) showed ~23.8% GFP-positive cells, nearly twofold higher than LNP-GFP (40) at ~12.6%. <b>Conclusions</b>: These results demonstrate the capability of microfluidic-prepared DNA-PEI-LNPs to improve DNA delivery and transgene expression through optimized formulation strategies and selection of appropriate preparation methods.