Acoustic levitation as a screening method for excipient selection in the development of dry powder vaccines

Spray drying is emerging as a promising technique to produce thermally stable powder vaccines containing viral vectors. One of the most important factors in developing dry powder vaccines is the selection of the excipient carrier, however this process is time intensive, and uses large amounts of costly viral material. In this work, an acoustic levitator modified with a hot air delivery system was evaluated for its ability to mimic spray drying and acts as a screening method for excipient selection. The ability of three binary excipient blends to stabilize a human type 5 adenovirus was evaluated through an in vitro activity assay based on the expression of green fluorescent protein. Dried particle size and shape, glass transition temperature, moisture content, and crystallinity of powders produced by levitation and spray drying were compared. The particles created in the acoustic levitator under moderate heat can be considered representative of the powders that would be produced via spray drying. Viral vector titre losses differ between the methods, however, the trends with respect to excipient performance remain the same. Key material characteristics such as particle morphology and thermal properties are conserved when using the levitator. The acoustic levitator is a good starting point for dry powder vaccine development, and can be used to identify promising excipients while consuming minimal amounts of the viral vector.