Effects of drying methods on physical properties and morphology of trehalose/mannitol mixtures

Solid-state properties of dried protein formulations are important for stability and functionality of the product. This study investigates how different drying technologies (freeze-drying with and without annealing, spray drying and spray-freeze drying) affect the structure and solid-state properties of a set of matrix formulations composed of trehalose (glass former) and mannitol (scaffolding agent) in five ratios. The dried materials were characterized using differential scanning calorimetry, thermogravimetric analysis, x-ray diffraction and scanning electron microscopy. The morphology of the dried matrix is determined by the drying technology and the composition. In all mixtures, mannitol partially dissolved in the amorphous trehalose, resulting in reduced glass transition temperature. At least 50% mannitol is required to achieve a scaffolding effect through crystallized mannitol. At 25% mannitol poor structural stability is obtained regardless of drying technology. Despite the vast differences in drying kinetics, all drying technologies resulted in similar amorphous content in the dried material.