The development of mRNA vaccines has increased rapidly since the COVID-19 pandemic. As one of the critical attributes, understanding mRNA lipid nanoparticle (LNP) stability is critical in the vaccine product development. However, the correlation between LNPs’ physiochemical characteristics and their potency still remains unclear. The lack of regulatory guidance on the specifications for mRNA LNPs is also partially due to this underexplored relationship. In this study, we performed a three-month stability study of heat-stressed mRNA LNP samples. The mRNA LNP samples were analyzed for their mRNA degradation, LNP particle sizes, and mRNA encapsulation efficiency. In vitro cell potency was also evaluated and correlated with these above-mentioned physiochemical characterizations. The mRNA degradation–cell potency correlation data showed two distinct regions, indicating a critical cut-off size limit for mRNA degradation. The same temperature dependence was also observed in the LNP size–cell potency correlation.

Implantable drug delivery systems formed upon injection offer a host of advantages, including localized drug administration, sustained release, minimized side effects, and enhanced patient compliance. Among the various techniques utilized for the development of in situ forming drug implants, solvent-induced phase inversion emerges as a particularly promising approach. However, synthetic polymer-based implants have been associated with undesirable effects arising from polymer degradation. In response to this challenge, a novel category of drug delivery systems, known as phospholipids-based phase separation gels (PPSGs), has emerged. These gels, characterized by their low initial viscosity, exhibit injectability and undergo rapid transformation into in situ implants when exposed to an aqueous environment. A typical PPSG formulation comprises biodegradable components, such as phospholipids, pharmaceutical oil, and a minimal amount of ethanol. The minimized organic solvents in the composition show good biocompatibility. And the relatively simple composition holds promise for industrial-scale manufacturing. This comprehensive review provides an overview of the principles and advancements in PPSG systems, with specific emphasis on their suitability as drug delivery systems for a wide range of active pharmaceutical ingredients (APIs), spanning from small molecules to peptides and proteins. Additionally, we explore the critical parameters and underlying principles governing the formulation of PPSG-based drug delivery strategies, offering valuable insights on optimization strategies.

MK-2048 is a second-generation integrase inhibitor active against HIV, which has been applied vaginally using ring formulations. In this work, a nanoparticle-in-film technology was developed as a discrete pre-exposure prophylactic product option against HIV for an extended duration of use. A film platform loaded with poly (lactic-co-glycolic acid) nanoparticles (PNP) encapsulating MK-2048 was engineered. MK-2048 PNPs were loaded into films that were manufactured via the solvent casting method. Physicochemical and mechanical properties, in vitro efficacy, Lactobacillus compatibility, in vitro and ex vivo permeability, and in vivo pharmacokinetics in macaques were evaluated. PNPs with a mean diameter of 382.2 nm and −15.2 mV zeta potential were obtained with 95.2% drug encapsulation efficiency. PNP films showed comparable in vitro efficacy to free MK-2048 (IC₅₀ 0.46 vs. 0.54 nM) and were found to have no impact on Lactobacillus. MK-2048 encapsulated in PNPs showed an increase in permeability (>4-fold) compared to the free MK-2048 in MDCKII cell lines. Furthermore, PNPs had higher ectocervical tissue permeability (1.7-fold) compared to free MK-2048. PNP films showed sustained drug levels for at least 3 weeks in the macaque vaginal fluid. This work demonstrates the synergy of integrating nanomedicine and polymeric film technology to achieve sustained vaginal drug delivery.