Soft mist inhaler nebulization by Rayleigh-breakup largely preserves functional integrity of liposomal mRNA in respirable aerosols

Inhalable mRNA is an emerging field holding great potential for applications as mucosal vaccination, antiviral therapy or protein replacement therapies, but efficient delivery remains a bottleneck. In this study, we explore the use of a Soft Mist Inhaler (SMI), based on Rayleigh-breakup, for pulmonary mRNA delivery. We found that the SMI successfully aerosolized GFP mRNA encapsulated in liposomes while maintaining colloidal stability, mRNA integrity and in vitro transfection efficiency in A549 cells. Furthermore, the device enabled simultaneous delivery of nucleic acids in various sizes using a model CRISPR/Cas13d system. The formulation could be reproducibly aerosolized with a low geometric standard deviation (GSD) and optimal aerosol droplet size for lung delivery. Based on the aerosol data, lung deposition modeling was conducted, indicating high lung deposition with minimal exhaled fraction. In comparison, aerosolization by a conventional Vibrating Mesh Nebulizer led to significant loss of nanoparticles and transfection efficiency. Utilizing SMIs may facilitate pulmonary delivery of mRNA nanoparticle formulations by lowering stability-associated hurdles while providing intrinsically high deposition in the lungs.