Better mRNA release inside cells boosts vaccine and gene editing performance, enabled by redesigned lipid molecules that grip cargo tightly but let go quickly once inside cells.
(Nanowerk Spotlight) A technology that proved transformative at the population level remains remarkably inefficient at the molecular level. The lipid nanoparticles behind the COVID-19 mRNA vaccines delivered protection to billions of people. Yet studies on small RNA molecules show that only 1 to 2% of the cargo these fat-based capsules carry ever reaches the cytoplasm, where it must arrive to produce protein.
For vaccines, this was sufficient to generate protective immunity, though higher efficiency could enable lower doses and fewer side effects. For more demanding applications such as gene editing and cancer immunotherapy, where higher and more precise protein expression is needed, the margin is far thinner.
The source of this inefficiency is a physical contradiction at the heart of lipid nanoparticle design. During assembly, ionizable lipids inside the particle must grip mRNA tightly through electrostatic attraction to keep it from degrading in the bloodstream. But once the particle enters a cell, that same electrostatic grip can persist, preventing the mRNA from detaching and reaching the translation machinery. Stronger packaging and easier release work against each other.
A study published in Advanced Materials (“Resolving the mRNA Encapsulation‐Release Trade‐off via Compensatory Forces in Engineered Ionizable Lipids”) describes a strategy to escape this trade-off. The research team engineered ionizable lipids (IL), the electrically active component of lipid nanoparticles (LNPs), to carry a second type of molecular attraction alongside the standard electrostatic charge. By grafting chemical groups capable of hydrogen bonding and van der Waals interactions onto the lipid tails, they created molecules where two forces cooperate during assembly but behave differently once inside a cell.
The logic rests on how these forces respond to distance. Electrostatic attraction works over long range and dominates when conditions favor it. Hydrogen bonds and van der Waals forces operate only at very close range and break easily when molecular contacts shift even slightly. At acidic pH, both types reinforce each other, locking mRNA tightly in place. At the neutral pH inside cells, the electrostatic component fades as the lipid headgroups lose their charge, and the close-range bonds, no longer supported, collapse rapidly. The mRNA is released.
Deciphering IL/mRNA interactions for rational LNP design. a) Balancing mRNA assembly and release via unraveling the IL/mRNA interactions. By integrating molecular dynamics simulations and experimental validations, we engineered ILs with H-bonding motifs to optimize mRNA-LNP interactions. This may compensate Coulombic (long-range) forces with short-range forces, enhancing mRNA encapsulation stability while enabling increased intracellular release, offering advanced strategies for improved vaccination and non-viral gene therapies. b) A workflow to integrate experimental data with coarse-grained molecular dynamics (CGMD) and all-atom molecular dynamics (AAMD) simulation, establishing the contact number merits to quantify IL/mRNA interactions for rational LNP design. (Image: reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
To test this idea, the researchers started with ALC0315, the ionizable lipid used in the BNT162b2 COVID-19 vaccine. They swapped a single chemical bond in one of its hydrocarbon tails with different functional groups: urea, carbamate, carbonate, amide, and ether. Each swap preserved the lipid’s ability to become charged at low pH while introducing varying degrees of close-range binding capacity.
The team used molecular dynamics simulations, computational models that track how atoms and molecules move and interact over time, to predict how each variant would behave with mRNA. From large-scale simulations of full nanoparticle assembly, they developed a “contact number” metric that counted lipid-mRNA interactions within a close-distance threshold. Urea, carbamate, and carbonate variants scored 3.9 to 7.6% higher than the original ALC0315.
More detailed atom-level simulations revealed finer detail: the urea variant formed 2.5 times more hydrogen bonds with mRNA than ALC0315. Nuclear magnetic resonance spectroscopy, a technique that detects molecular interactions, confirmed these predictions in the lab.
Physical measurements aligned with the computational results. Atomic force microscopy showed that urea-containing nanoparticles had roughly double the internal cohesion of ether-based particles. X-ray scattering revealed tighter internal packing.
Because the added close-range forces compensated for some of the electrostatic binding, the team could reduce the ionizable lipid content from 50% to 40% without losing encapsulation efficiency. At this lower lipid ratio, the urea-containing nanoparticles released mRNA faster under conditions mimicking the cell interior, and intramuscular injection in mice produced stronger protein expression than any other formulation tested.
To demonstrate that the principle works beyond a single molecular scaffold, the researchers applied it to a structurally different lipid series. The resulting variant, called OT13, combined branched hydrocarbon chains with a urea group. OT13-based nanoparticles loaded mRNA almost completely, with only 2.1% of particles remaining empty compared with 7.3% for the control.
In a herpes zoster vaccine model, OT13 nanoparticles generated roughly three times more antigen-specific T cells producing the immune signaling molecules interferon-gamma and IL-2 than the control. In a melanoma model, they shrank tumors by 77.9% relative to ALC0315-based nanoparticles and extended median survival from 32 to 38 days.
The formulation also performed well in liver-targeted gene editing. Loaded with Cas9 mRNA and a guide RNA targeting the transthyretin gene, which encodes a blood protein involved in thyroid hormone and vitamin A transport, OT13 nanoparticles delivered at 0.5 mg kg⁻¹ matched ALC0315 in editing efficiency. Yet they produced a far stronger functional outcome: serum transthyretin protein fell by more than 90%, versus roughly 58% for ALC0315. I
nflammatory markers showed no significant differences between groups, suggesting the improvement stemmed from more efficient mRNA release and translation rather than off-target immune effects.
By pairing two types of molecular force with opposing distance sensitivities, this lipid engineering approach turns a fundamental constraint of lipid nanoparticle design into an advantage. The same particle can hold its cargo tightly during transit and release it efficiently once inside a cell. With demonstrated gains across vaccination, cancer immunotherapy, and CRISPR gene editing, compensatory-force engineering may offer a practical route toward more potent mRNA medicines.
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Yufei Xia (Institute of Process Engineering, Chinese Academy of Sciences)
, 0000-0003-1215-6128 corresponding author
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