How do you qualify a scale-down model for process development?

Scale-down model qualification demonstrates that small-scale mimics manufacturing-scale performance. Approach includes: identifying critical aspects to replicate (kLa, mixing time, shear), designing scale-down geometry (maintaining relevant dimensionless numbers), comparing performance at both scales (growth kinetics, productivity, quality attributes), and establishing statistical equivalence for key outputs. Parameters that cannot be matched (e.g., hydrostatic pressure, gradient response) are documented and implications assessed. For cell culture, typical scale-down ratios are 1000-2000x. Multivariate analysis comparing product quality attributes strengthens qualification. Requalification is needed when manufacturing process changes. A qualified model enables valid process characterization studies.