Name: Video: Optimized Formulation of Lipid Nanoparticles Using a Two-Jet Continuous Impinging Jet (CIJ) Mixer
Uploaded: 2024-08-23T13:50:00
Duration: 2 min 23 s
Description: 531 Views. Optimized Formulation of Lipid Nanoparticles Using a Two-Jet Continuous Impinging Jet (CIJ) Mixer

optimized formulation of lipid nanoparticles using a two-jet continuous impinging jet (cij) mixer

Synthesizing Lipid Nanoparticles Using CIJ and &#181;MIVM Mixer Technologies

mRNA-based therapeutics hold great potential for the treatment and prevention of a wide range of diseases, including infectious diseases, genetic disorders, and cancers1. Unlike small-molecule therapeutics, which can passively diffuse across the cell membrane, nucleic acids must be encapsulated for intracellular delivery2. Encapsulation provides both structure and stability to mRNA, facilitating their intracellular delivery via endocytic pathways as well as preventing degradation from intra- and extra-cellular components such as nucleases3. A host of materials and nanocarriers have been developed for the encapsulation and delivery of mRNA, including inorganic nanoparticles, polymers, lipids, and lipid-like materials1. Among these, LNPs have emerged as the most prominent delivery platform for mRNA-based therapeutics4.
LNPs are composed of four lipid components: ionizable lipid, cholesterol, zwitterionic lipid, and PEG-lipid stabilizer5. Ionizable lipids suitable for mRNA delivery exhibit a careful balance between the lipid hydrophobicity and the dissociation constant (pKa) of a ternary amine group6. The ionizable lipid pKa typically has a pH between 6.0 and 6.7, such as KC-2 (DLin-KC2-DMA), MC-3 (DLin-MC3-DMA), and ALC-03157. This pKa restriction on the ionizable lipid enables both the encapsulation of nucleic acid polymers as hydrophobic lipid salts and the intracellular delivery through an &#34;endosome escape&#34; process. LNPs enter a target cell through (various) endocytosis pathways that all involve acidification of the endosome from pH 7.4 to pH ~58. The ionizable lipid pKa ensures that LNPs have nearly neutral surfaces under physiological conditions but become cationic in an acidifying endosome9. This pH response enables selective disruption of only the endosomal membrane, the release of the encapsulated nucleic acid polymer, and preserves cell viability, unlike permanently cationic lipids used in transfection systems such as Lipofectamine. Cholesterol is a hydrophobic, interstitial molecule in the LNP structure that improves lipid fluidity. The zwitterionic lipid plays a structural role and forms a bilayer on the LNP surface. The poly(ethylene glycol)-lipid (PEG-lipid) is a colloidal stabilizer that enhances the LNP stability by imparting a polymeric steric stabilizer onto the LNP surface, which resists aggregation of LNPs. This stabilizes the LNP, particularly during changes in pH that regenerate the free base form of the ionizable lipid which behaves like a hydrophobic oil. The Onpattro (patisiran) recipe (hereafter, referred to as LNP formulation) is often used as a starting point for LNP formulation with ionizable lipid MC3, cholesterol, distearoylphosphatidylcholine (DSPC), and PEG2000-DMG dissolved in ethanol mixed against an aqueous solution of RNA10.
Several techniques can be used to manufacture LNPs encapsulating nucleic acid polymers, with most of them relying on a common theme of rapidly mixing an ethanol stream containing lipids with an aqueous stream incorporating the nucleic acid of interest (siRNA, mRNA, or DNA)9,11,12,13,14. In this regard, bulk mixing processes such as pipette mixing and vortex mixing offer a simple strategy to form LNPs that eliminates the need for using sophisticated instruments12. However, bulk mixing does not provide a homogeneous distribution of components, leading to a sub-optimal LNP size distribution along with significant batch-to-batch variability15.
Laboratories routinely use microfluidic mixing techniques to obtain reproducible LNPs by achieving more precise control over mixing conditions12,13,16. Yet, the laminar flow conditions in microfluidic devices, which are inherent due to the small length scales and low velocities in a microfluidics chamber, result in comparatively slow solvent/antisolvent mixing17. The small chamber dimensions severely limit the throughput and scalability needed for GMP production of LNPs, but researchers have parallelized microfluidic chambers to attempt to scale production volumes15. A parallelized microfluidics geometry does not eliminate the problem of lipid adsorption to surfaces during large volume processing, a problem commonly referred to as &#34;fouling&#34; of the mixing device, and there are problems with uniformity and stability of flows that make microfluidics scaleup challenging for industrial-scale production18,19. It is not surprising that pharmaceutical companies used turbulent impinging jet mixers to manufacture COVID-19 vaccination mRNA-LNPs20.
The production process of RNA-loaded LNPs entails the blending of an aqueous buffer stream containing the RNA payload with an ethanol stream containing the four distinct lipid components. These formulations utilize an acidic buffer with a pH of 4.0 or less, which charges the ionizable lipid as the aqueous and ethanolic streams mix. The positively charged ionizable lipids interact electrostatically with the negatively charged RNAs, forming a hydrophobic RNA-lipid salt. Hydrophobic lipid species, including the RNA-lipid salt, precipitate in the mixed solvents and form hydrophobic nuclei. These nuclei grow through the precipitation of zwitterionic lipid and cholesterol until reaching a critical point where sufficient pegylated lipid adsorbs on the surface of the LNPs, halting further growth -nucleation and growth mechanism21,22,23. The addition of aqueous buffer to the lipid solution, to the extent where lipids precipitate and LNPs form, hinges on two distinct time scales: the solvent-antisolvent mixing period, &#964;mix, and the nuclei growth period, &#964;agg. The dimensionless Damk&#246;hler number, defined as Da = &#964;mix/&#964;agg, captures the interplay between these time scales24. In instances of slow mixing (Da &#62; 1), the final size of LNPs is transport-controlled and varies with mixing time. Conversely, during fast mixing (Da &#60; 1), the fluid is fragmented into Kolmogrov-length striations or layers, whereby LNP formation is solely governed by the molecular diffusion of each constituent, resulting in homogeneous kinetics of LNP formation. Achieving the latter scenario demands that the lipid concentration exceeds a critical threshold, establishing a state of supersaturation conducive to uniform homogeneous nucleation.
It is estimated that &#964;agg ranges from a few tens to a few hundreds of milliseconds25. In its most basic configuration, the two streams, one containing ethanol with lipids and the other containing an aqueous buffer with RNA cargo, are injected into a chamber known as a &#34;confined impinging jet&#34; (CIJ) mixer. Turbulent vortices produce solvent/antisolvent striation length scales of 1 &#181;m within 1.5 ms when operated at appropriate velocities. The stream velocities and mixing geometry determine the conversion of linear momentum into turbulent vortices that mix the streams. This is parameterized by the dimensionless number, the Reynolds number (Re), that is linearly proportional to the flow velocities. Re is computed from Re = &#931; (ViDi/vi), where Vi is the flow velocity in each steam, vi is the kinematic viscosity of each stream, and Di is the stream inlet diameter in 2-jet CIJ devices26 or the chamber diameter in 4-jet MIVMs27. Note: Some references for the CIJ use only a single jet diameter and velocity to define Re28. Re is in the range of 1-100 in a microfluidics device, whereas in the CIJ devices, Re of 125,000 can be achieved. In a CIJ mixer, streams with equal momentum collide, dissipating their momentum upon impact as turbulent mixing, which leads to efficient micromixing due to the small Kolmogorov microscales and small Damk&#246;hler number. Another type of mixer is the &#34;multiple inlet vortex mixer&#34; (MIVM), where four streams are directed into a central chamber. In this setup, continuous flows into the confined mixing chamber ensure a well-defined mixing time scale. All fluid elements pass through the high-energy mixing zone in both types of mixers. In contrast, simple mixing devices like T-junctions do not contain a chamber that provides a mixing zone, resulting in less mixing of the two streams due to the incoming stream momentum being largely deflected into the outlet direction rather than into turbulent vortex generation. Both CIJ and MIVM mixers can be operated in batch or continuous modes, offering flexibility for LNP production at various scales.
This protocol describes how optimal LNP formulations are made by employing two confined impinging jet technologies: 2-jet CIJ and the 4-jet MIVM mixers. The operation of CIJ and MIVM mixers has been previously demonstrated for the preparation of NPs with hydrophobic core materials29. That article and video should be consulted as an additional resource on the formation of NPs with these mixers. This update focuses on lipid-based NP formation. The ability to tune the size of LNPs by varying the micro-mixing conditions is demonstrated. Additionally, the utility of CIJ technologies in forming stable, monodisperse LNPs with improved in vitro transfection efficiencies in HeLa cells when compared to LNPs made using poor pipette mixing is shown. Furthermore, the advantages and disadvantages of each CIJ mixing geometry, along with appropriate conditions needed for the scaleup of these mixers, are discussed.

Author Spotlight: Enhancing Lipid Nanoparticle Formation Through Turbulent Mixing in Confined Geometries

Synthesizing Lipid Nanoparticles by Turbulent Flow in Confined Impinging Jet Mixers

Optimized Formulation of Lipid Nanoparticles Using a Two-Jet Continuous Impinging Jet (CIJ) Mixer

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Research

JoVE Journal

Bioengineering

531 Views. Optimized Formulation of Lipid Nanoparticles Using a Two-Jet Continuous Impinging Jet (CIJ) Mixer

Video: Optimized Formulation of Lipid Nanoparticles Using a Two-Jet Continuous Impinging Jet (CIJ) Mixer

Lipid nanoparticles (LNPs) have demonstrated their enormous potential as therapeutic delivery vehicles, as evidenced by the approval and global usage of two COVID-19 messenger RNA (mRNA) vaccines. On a small scale, LNPs are often made using microfluidics; however, the limitations of these devices preclude their use on a large scale. The COVID-19 vaccines are manufactured in large quantities using confined impinging jet (CIJ) turbulent mixers. CIJ technology enables production at a laboratory scale with the confidence that it can be scaled to production volumes. The key concepts in CIJ mixing are that the mixing length and time scale are determined by the turbulence intensity in the mixing cavity and that the nanoparticle formation occurs away from walls, eliminating the problem of deposition on surfaces and fouling. This work demonstrates the process of making LNPs using confined impinging jet mixer technology with two geometries: the two-jet CIJ and the four-jet multi-inlet vortex mixer (MIVM). The advantages and disadvantages of each mixing geometry are discussed. In these geometries, LNPs are formed by rapid mixing of an organic solvent stream (usually ethanol containing the ionizable lipids, co-lipids, and stabilizing PEG-lipids) with an aqueous anti-solvent stream (aqueous buffer containing RNA or DNA). The operating parameters for the CIJ and MIVM mixers are presented to prepare reproducible LNPs with controlled size, zeta potential, stability, and transfection effectiveness. The differences between LNPs made with poor mixing (pipetting solutions) compared to CIJ mixing are also presented.

A detailed protocol for synthesizing lipid nanoparticles (LNPs) using confined impinging jet (CIJ) mixer technologies, including a two-jet CIJ and a four-jet multi-inlet vortex mixer (&#181;MIVM), is demonstrated. The CIJ mixers generate reproducible, turbulent micro-mixing environments, resulting in the production of monodisperse LNPs.

Lipid nanoparticles (LNPs) have demonstrated their enormous potential as therapeutic delivery vehicles, as evidenced by the approval and global usage of ...