Microstructure evolution during nano-emulsification by NMR and microscopy

Molecular localization and exchange kinetics in pharmaceutical liposome and mRNA lipoplex nanoparticle products determined by small angle X-ray scattering and pulsed field gradient NMR diffusion measurements

We have used pulsed field gradient (PFG)-NMR diffusion experiments, also known as DOSY, in combination with small angle X-ray scattering measurements to investigate structure and molecular exchange dynamics between pharmaceutical lipid nanoparticles and the bulk phase. Using liposomes and lipoplexes formed after complexation of the liposomes with messenger mRNA as test systems, information on dynamics of encapsulated water molecules, lipids and excipients was obtained. The encapsulated fraction, having a diffusivity similar to that of the liposomes, could be clearly identified and quantified by the NMR diffusion measurements. The unilamellar liposome membranes allowed a fast exchange of water molecules, while sucrose, used as an osmolyte and model solute, showed very slow exchange. Upon interactions with mRNA a topological transition from a vesicular to a lamellar organization took place, where the mRNA was inserted in repeating lipid bilayer stacks. In the lipoplexes, a small fraction of tightly bound water molecules was present, with a diffusivity that was influenced by the additional presence of sucrose. This extended information on dynamic coherencies inside pharmaceutical nanoparticle products, provided by the combined application of SAXS and PFG-NMR diffusion measurements, can be valuable for evaluation of quality and comparability of nanoscaled pharmaceuticals.

Effect of surfactant concentration on diffusion and microstructure in water-in-oil emulsions studied by low-field benchtop NMR and optical microscopy

Emulsions are ubiquitous in many consumer products, including food, cosmetics and pharmaceuticals. Whilst their macroscopic characterisation is well-established, understanding their microscopic behaviour is very challenging. In our previous work we investigated oil-in-water emulsions by studying the effect of water on structuring and dynamics of such systems. In the present work, we investigate the effect of surfactant concentration on microstructure and diffusion within the water-in-oil emulsion system by using low-field pulsed-field gradient (PFG) NMR studies carried out with a benchtop NMR instrument, in conjunction with optical imaging. The results reveal that at high surfactant concentration the formation of smaller droplets gives rise to a third component in the PFG NMR attenuation plot, which is mostly attributed to restricted diffusion near the droplet boundaries. In addition, structuring effects due to increase in surfactant concentration at the boundaries could also contribute to further slowing down water diffusion at the boundaries. As the surfactant concentration decreases, the average droplet size becomes larger and both restriction and structuring effects at the droplet boundaries become less significant, as suggested by the PFG NMR plot, whereby the presence of a third diffusion component becomes less pronounced.

NMR diffusometry: A new perspective for nanomedicine exploration

Nuclear Magnetic Resonance (NMR) based diffusion methods open new perspectives for nanomedicine characterization and their bioenvironment interaction understanding. This review summarizes the theoretical background of diffusion phenomena. Self-diffusion and mutual diffusion coefficient notions are featured. Principles, advantages, drawbacks, and key challenges of NMR diffusometry spectroscopic and imaging methods are presented. This review article also gives an overview of representative applicative works to the nanomedicine field that can contribute to elucidate important issues. Examples of in vitro characterizations such as identification of formulated species, process monitoring, drug release follow-up, nanomedicine interactions with biological barriers are presented as well as possible transpositions for studying in vivo nanomedicine fate.