A solid-state NMR study of molecular mobility and phase separation in co-spray-dried protein-sugar particles

Molecular mobility and physical form of co-spray-dried sugar-lysozyme formulations were evaluated. Co-spray-dried trehalose:lysozyme and sucrose:lysozyme formulations in 1:9, 1:1 and 9:1 ratios (w:w) were stored at 0% RH and 75% RH for 5-6 days. Molecular mobility and physical form of the co-spray-dried formulations after storage were determined by using 13C and 1H solid-state NMR as well as X-ray powder diffractometry. The results showed that increasing sugar content in co-spray-dried formulations stored at 0% RH decreased molecular mobility of the amorphous formulations indicating a close association of the protein and sugar. Exposure of sugar-lysozyme 1:1 and 9:1 formulations to 75% RH led to separation of sugar and protein phases, where the sugar phase was crystalline. The intimate sugar-lysozyme interaction of the formulations stored at 0% RH and the phase separation of the sugar-rich formulations stored at 75% RH were also confirmed by using 13C solid-state NMR spin-lattice relaxation time-filter (T1-filter) measurements. The propensity of sucrose and trehalose to crystallise was similar; however, the results suggest that part of the sugar in the phase-separated formulations remained amorphous and in close association with lysozyme.