Scale-down models (SDM) are physical, small-scale models of commercial-scale unit operations or processes that are used throughout the biopharmaceutical industry for validation studies, commercial deviation investigations, and postapproval process improvements. To support these studies, regulatory guidelines state that SDMs should be representative of the commercial process. For some downstream unit operations such as column chromatography, developing a representative SDM is straightforward because a linear scale-down approach can be used. However, developing a representative SDM for other downstream unit operations such…