Fast crystal growth of amorphous nimesulide: implication of surface effects

Understanding crystallization behaviors is of utmost importance for developing robust amorphous pharmaceutical solids. Herein, the crystal growth behaviors of amorphous anti-inflammatory drug nimesulide (NIME) are systemically investigated in the glassy and supercooled liquid state as a function of temperature. A sudden over-tenfold increase is observed in the bulk crystal growth of NIME on cooling below its glass transition temperature (T_g). This fast growth behavior is known as a glass-to-crystal (GC) mode and has been reported in some molecular glasses. Fast surface crystal growth of NIME can persist up to T_g + 57°C with a weak jump in its growth rates at 30-40°C. In addition, surface crystal growth and GC growth of NIME exhibit an almost identical temperature dependence, supporting the view that GC growth is indeed a surface-facilitated process. Moreover, the bubble-induced fast crystal growth of NIME is observed in the interior of its supercooled liquid with approximately the same growth kinetics as surface crystal growth. These findings are relevant for a full understanding of the surface-related crystallization behaviors and physical stability of amorphous pharmaceutical formulations.