Single-use mixing systems for protein products: Evaluation of dissolution performance and mechanical stress

Sterile manufacturing (fill & finish) of biologic drug products involves critical operations like freezing/thawing, mixing, filtration, and filling. These processes must be well characterized to understand their impact on product quality. While single-use systems offer efficiency and flexibility, they also introduce challenges related to aseptic handling and material compatibility with biological formulations. For the unit operation "mixing", equipment configurations vary, each with distinct advantages and limitations. In this study, we systematically compared the performance of two single-use mixing systems using drug substance bottles, equipped with a top-mounted impeller (TMM), a novel bottom-mounted impeller (BMM), and a conventional magnetic stirrer (MS). Mixing efficiency, measured by changes in conductivity reported as dissolution time, was evaluated across scale-up parameters, including container size, fill volume, and impeller tip speed. Dissolution time was dependent on mixer type and inversely correlated to tip speed and impeller diameter/bottle diameter ratio. BMM and TMM showed consistently lower dissolution times and less challenges compared to MS, which showed insufficient mixing quality for some configurations. Mechanical stress during mixing was assessed using a model protein, with results corroborated through computational fluid dynamics (CFD) simulations. Mechanical stress was dependent on mixer type and fill volume and lead to adverse product quality impact of the model protein, which became less pronounced with higher fill volume. The adverse impact on product quality was generally higher and more variable when using the MS than with the BMM. These findings provide formulation and process development scientists with data-driven guidance for selecting appropriate mixing technologies for biologic drug manufacturing and scaling-up processes.