Cryomilling of freeze dried low-Tg sugar glasses: A versatile method to prepare inhalable dry powder formulations

Pulmonary delivery may offer significant advantages for the administration of certain biologics, but its success relies on the development of dry powder formulations that are both stable and respirable. Low-glass transition temperature (Tg) sugars are widely used as stabilizing excipients, yet their application in pulmonary formulations is limited by poor physical stability during conventional processes such as spray drying or jet milling. These methods generate heat that can exceed the Tg, causing crystallization and loss of stabilizing properties. Cryomilling provides a potential solution by milling freeze dried cakes under cryogenic conditions. In this study, freeze dried sucrose, maltose, isomalt, trehalose, and lactose were cryomilled for 3, 5, 7, or 9 cycles without or with either leucine or trileucine. Physicochemical properties were assessed using X-ray powder diffraction (XRPD), modulated differential scanning calorimetry (mDSC), and dynamic vapor sorption (DVS). Furthermore, the primary particle size and the particle size and dispersion efficiency from the Cyclops DPI were analyzed by laser diffraction, while aerodynamic performance of the cryomilled dry powder formulations was measured using cascade impaction analysis. The number of cryomilling cycles did not affect primary particle size of any of the cryomilled formulations. Furthermore, sucrose, maltose, isomalt and lactose cryomilled with either 4% leucine or trileucine demonstrated superior dispersibility from the Cyclops DPI compared with formulations containing no excipient. Cascade impaction analysis confirmed that cryomilling each of the 5 freeze dried sugars with 4% trileucine achieved aerodynamic characteristics suitable for deep lung deposition. In conclusion, cryomilling of freeze dried low Tg sugars with 4% trileucine enables the production of inhalable powders from low-Tg sugars with optimal dispersibility and pulmonary performance. This approach may provide a foundation for future investigations into pulmonary delivery of biologics.