Microfluidic technologies and devices for lipid nanoparticle-based

Purpose: RNA-loaded lipid nanoparticles (LNPs) are clinically validated for siRNA and mRNA delivery, but their therapeutic performance depends critically on reproducible control of size, size distribution, zeta potential, and RNA encapsulation efficiency. Microfluidic devices offer precise mixing, rapid ethanol dilution, high reproducibility, high-throughput formulation screening, and continuous production, making them attractive for standardized LNP manufacturing.

Hypothesis: If RNA-loaded LNPs are produced using microfluidic devices with controlled ethanol dilution and optimized lipid composition, N/P ratio, and flow conditions, then LNP size, PDI, surface charge, and RNA encapsulation efficiency can be precisely tuned, enabling improved siRNA, mRNA, and ribonucleoprotein (RNP) delivery for RNA therapy and genome editing.

Aims: Introduce microfluidic devices and the mechanism of LNP formation via ethanol dilution. - Review microfluidic production of LNPs for siRNA, mRNA, and RNP delivery. - Summarize applications in RNA-based therapy, vaccines, and CRISPR-Cas9 genome editing. - Discuss advantages, limitations, and future outlook for microfluidic LNP production.

Delivery system: Platform: lipid nanoparticles (LNPs) produced by microfluidic mixing. - Key lipid components: cationic or pH-sensitive ionizable lipids; phospholipids such as DSPC and DOPE; cholesterol; PEG-lipids such as DMG-PEG, C14-PEG, DSPE-PEG. - Payloads: siRNA, mRNA, Cas9 mRNA/sgRNA, CRISPR-Cas9 RNPs, single-stranded oligonucleotides (ssON), plasmid DNA, and other nucleic acids. - Microfluidic device types: T-/Y-shaped; sheath-flow (3-inlet); chaotic mixer (e.g., NanoAssemblr); planar asymmetric split-and-recombine micromixer; iLiNP baffle device; capillary, electrohydrodynamic, ultrasound, and 3D-printed micromixers. - Targeting/functionalization: transferrin, peptides, antibodies, Glu-urea-Lys ligands, and SORT (selective organ targeting) molecules such as DOTAP or 18PA for lung, spleen, or liver targeting.

Approach: Review and synthesis of in vitro, in vivo, and clinical literature. Cited models include HeLa, HepG2, HEK293, primary hepatocytes, Jurkat, Nalm-6, K562, Vero, dendritic cells, T cells, and CLL cells; in vivo models include mice, rats, rabbits, ferrets, and non-human primates. Disease contexts include COVID-19, liver gene silencing, cancer, Zika, HBV, genetic disorders, and genome editing. As a review, it reports no primary experimental groups, n values, doses, or controls.

Key methods: No primary methods. The review discusses data generated by cited studies using: - Dynamic light scattering for size, PDI, and zeta potential. - RNA encapsulation efficiency assays. - In vitro luciferase/GFP expression and gene-silencing assays. - In vivo biodistribution and expression imaging (e.g., IVIS). - CRISPR-Cas9 gene editing and DNA cleavage assays. - Stability, cytokine induction, and toxicity measurements.

Key results: Increasing PEG-lipid from 1 to 5 mol% reduced siRNA-LNP size from 54 nm to 28 nm; DLin-KC2-DMA LNPs achieved 50% FVII silencing at 0.01 mg/kg in mice. - Optimized mRNA-LNP formulations improved delivery and expression 3-fold, and EPO mRNA expression 7-fold relative to the original formulation. - SORT LNPs enabled organ-selective delivery: positively charged DOTAP favored lung, negatively charged 18PA favored spleen, and neutral formulations favored liver. - RNP-loaded LNPs achieved 95% EGFP knockout using 5 nM spCas9 RNP in HEK-GFP cells. - sgPLK1-cLNPs achieved up to 70% PLK1 gene editing, inhibited tumor growth by 50%, and improved survival by 30%; EGFR-targeted LNPs improved overall survival by 80%. - Microfluidic screening of 70 lipidoids produced more hit compounds for LNPs than for lipoplexes, supporting improved carrier discovery. - Onpattro (patisiran) was the first approved siRNA drug produced using a microfluidic device; COVID-19 mRNA vaccines were authorized in 2020–2021.

Interpretation: The authors conclude that microfluidic devices and technologies enable reproducible, size-controlled, and scalable production of RNA-loaded LNPs. They argue that microfluidics will become the gold standard for LNP production, accelerating RNA therapeutics, vaccines, genome editing, and personalized nanomedicine.

Limitations: Review article; no primary data, effect sizes, n values, doses, or controls. - Most microfluidic devices are PDMS-based and suitable for laboratory scale; mass production requires glass or metal devices with robust microchannel designs. - Ethanol exposure during production can denature RNPs; rapid dilution is required. - RNP-LNP studies are fewer than siRNA/mRNA studies. - Scale-up, GMP manufacturing, long-term stability, cold-chain requirements, and regulatory validation remain challenges. - Clinical translation of many LNP-RNA systems is still early-stage.