As a chemist I was always in a hurry to perform a DoE for optimizing a chemical reaction. More often I failed and gradually I learned that it can’t be done in a hurry, we need to do some homework before that.
Basic concept behind QbD is the Juran’s concept of “building/designing quality into the product”[i] rather than “complying product with the quality”. Designing quality into the product could be achieved by having better control on the process and this can be achieved by proper understanding of the relationship between the CQAs (y) and CPPs/CMAs (x) as shown in Figure 4 and 7. This concept of building quality into the product is based on the quality risk management[ii] where one needs to assess the risk of each PPs/MAs on CQAs. Basic outline of QbD in process development is shown in Figure 9. It involves following steps
For a successful DoE, we need to divide the whole process into two phases
Phase-1: Preparing for DoE
It deals with the preliminary homework, like
what quality parameters we want to study & why?
What are the process parameters and material attributes that can affect the selected quality parameters?
Phase-2: Performing DoE and analysis followed by proposing the control strategy
Once quality parameters and most probable process parameters and material attributes are identified, its time for performing DoE to establish cause and effect relationship between the two.
Based on the DoE study, CPPs and CMAs are identified and a design space is generated within which CPPs & CMAs could be varied to keep CQAs under control.
Finally, before commercialization, a control strategy is proposed to keep CPPs/CMAs under specified range, either by proposing a engineering or manual control.
DoE: Design of Experiment
CQA: Critical quality attribute —these qualities of the product is critical for the customers
CPP: critical process parameters — these process parameters affects CQAs
CMA: Critical Material Attributes — These are input material attributes affecting the CQAs.
[i]. Juran on Quality by Design: The New Steps for Planning Quality Into Goods and Services, J. M. Juran, Simon and Schuster, 1992
[ii]. José Rodríguez-Pérez, Quality Risk Management in FDA-Regulated Industry, ASQ Quality Press, Milwaukee, 2012.