Optimization of continuous spin-freeze-drying: The role of spin-freezing on quality attributes and drying efficiency of a model peptide formulation

Continuous spin-freeze-drying is an innovative pharmaceutical manufacturing approach offering real-time monitoring and control at the individual vial level, unlike conventional batch lyophilization. A central feature of this technology is spin-freezing, which involves rapidly spinning liquid-filled vials under a precisely controlled cold gas flow, resulting in a thin, uniform frozen product layer. Using a model peptide formulation, we investigated the impact of different cooling and crystallization rates on quality attributes (QA) and primary drying duration. Key QAs included monomer content, peptide assay, moisture content, and pore structure. The monomer content, peptide content, and primary drying duration remained consistent across all spin-freezing conditions. However, scanning electron microscopy (SEM) and Karl Fischer titration revealed that freezing parameters significantly influenced pore structure and residual moisture content. Samples with smaller pores displayed lower residual moisture, as larger surface areas facilitate moisture desorption. Variations in freezing parameters also significantly impacted desorption kinetics during secondary drying. Slower crystallization rates led to more cracks and less shrinkage in the cake structure, while faster rates resulted in more uniform, stable cakes. Although specific to the product under study, these findings highlight the crucial role of spin-freezing in enhancing freeze-drying efficiency and product quality of biopharmaceuticals.