Modelling of Amorphous to Crystalline Transformation in a Drying Droplet/Particle

Spray drying is widely applied in the pharmaceutical industry for the formulation of particulate materials such as solid dispersions, excipients, active pharmaceutical ingredient (API) as well as co-dried materials (API with excipient). It converts pumpable feed into dry powder in a single unit operation. In spray drying, the atomised droplets typically range from 10 to 500 μm in diameter and comprise dissolved solute in a solvent. The droplets undergo rapid evaporation of solvent upon contact with a turbulent hot gas flow, favouring the formation of amorphous particles with a higher dissolution rate compared to the crystalline form.

However, amorphous particles can be unstable and transform to the crystalline form when exposed to high temperature and humid conditions, which reduces its efficacy. Furthermore, the distributions of particle size, densities and moisture contents also influence the product performance. By optimising the input operating conditions and feed composition in the spray dryer, it is possible to control the dried powder attributes.

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