An Investigation of Water Vapor Sorption for Improving Reconstitution Pathways of Freeze-Dried Lipid Nanoparticles Stabilized by Trehalose/Mannitol Excipients

Abstract

Lipid-based nanocarriers have been intensively developed to achieve controlled drug delivery and maintain pharmacological stability, especially, for mRNA-based vaccines. Freeze-drying is commonly recognized as a key technique that allows nanoparticles to be converted into a dry form, stored under ambient conditions, and reconstituted at time of use. This study investigated the influence of reconstitution conditions of freeze-dried lipid nanoparticles (LNPs) stabilized with trehalose or trehalose/mannitol mixtures on disintegration and aggregation upon rehydration. Direct water pipetting and water vapor sorption methods were applied to reconstitute the freeze-dried specimens. When LNPs were reconstituted by the water pipetting, a slight decrease in particle size and a significant increase in particle number concentration were observed. On the other hand, when reconstituted by the pipetting subsequent to the water vapor sorption, slight increases in particle size and particle number concentration were observed. These results suggested that the water pipetting lead significant disintegration of LNPs whereas the water vapor sorption inhibited the particle damage and lead slight aggregation. However, when the duration of the water vapor sorption time was prolonged, the LNPs could be disintegrated due to the crystallization of trehalose. The addition of mannitol delayed the trehalose crystallization, and restricted the disintegration of LNPs upon rehydration. A practical suggestion based on this study would be to use a formulation of trehalose and mannitol mixture, allow it to absorb water vapor until the glass–rubber transition, and rehydrate before the crystallization of trehalose, which would be an appropriate reconstitution path to allow the LNP to be retained its original formation.