The development, optimization, and analysis of downstream processes are challenged by a high number of potentially critical process parameters that need to be investigated using lab-scale experiments. These process parameters are spread across multiple unit operations and potentially show interactions across unit operations. In this contribution, we present a novel strategy for bioprocess development that considers the risk of parameter interactions across unit operations for efficient experimental design. A novel risk assessment tool (interaction matrix) is introduced to the Quality by Design (QbD) workflow. Using this tool, the risk of interaction across unit operations is rated. Subsequently, a design of experiments (DoE) across unit operations is conducted that has the power to reveal multivariate interdependencies. The power of the presented strategy is demonstrated for protein isolation steps of an inclusion body process, focusing on the quality attribute inclusion body purity. The concentration of Triton X-100 in the course of inclusion body (IB) purification was shown to interact with the g-number of the subsequent centrifugation step. The presented strategy targets a holistic view on the process and allows handling of a high number of experimental parameters across unit operations using minimal experimental effort. It is generically applicable for process development along QbD principles.
Keywords: design of experiments; inclusion body purity; interaction across unit operations; process development; quality by design; risk assessment.