Investigation of the felodipine glassy state by atomic force microscopy.

The glassy state of felodipine was prepared by melting crystals of felodipine on a clean glass slide and cooling to room temperature. It has been confirmed that glassy felodipine is a metastable state, and undergoes transformation to the more stable crystalline form. Crystallization occurred slowly and spontaneously at room temperature, below the glassy state transition temperature (Tg). The contact mode of atomic force microscopy was used for topographical imaging of the glassy and crystalline states of felodipine. When the glassy felodipine region next to the recrystallized zone was exposed to controlled mechanical stress through the tip, rapid additional crystallization was observed. This crystallization process can be induced and imaged in real time by atomic force microscopy.