Chen Mao

Abstract: Assessment of powder flow obstruction using principles of continuum mechanics – Implications in drug product manufacturing
• The existing industrial practice (judgment of flow by flow function coefficient) is good, but not sufficient. Density and stress are two main factors not considered in the flow function-based criteria.
• Multiple powder flow risks at all scales can be evaluated (including flow pattern, formation of arch, formulation of stable rathole) with relatively simple experimental procedures, using shear cell tester and wall friction measurements only.
• Study shows that nearly all pharmaceutical powders will take on funnel flow pattern using the modern IBCs.
• Although the traditional hopper design industry focuses on passive stress state, the active stress state (i.e. stress before powder starts to discharge) is a much higher risk for pharmaceutical industry and should be given greater attention.
• Wall friction generally helps with powder flow – although reduced wall friction may increase the chance of powder to flow under mass flow pattern, it also increases the powder stress at the bin outlet under active stress state, and thus increasing the risk of flow obstruction. Wall friction should be given with more scrutiny for pharmaceutical powder flow assessment.

Dr. Chen Mao is a Senior Scientist in the Small Molecule Pharmaceutics group at Genentech, Inc. He received his Ph.D. in industrial and Physical Pharmacy from Purdue University in 2006. Prior to joining Genentech, he assumed various scientist positions at XenoPort and Schering-Plough. His primary work involves formulation development and materials science of solid dosage forms. Dr. Mao is the co-chair of the Materials Science and Predictive Modeling Working Group of the IQ Consortium. He is an Adjunct Assistant Professor in the College of Pharmacy at the University of Texas at Austin. He also serves in the editorial board of Drug Development and Industrial Pharmacy. Dr. Mao’s research interests involve understanding and processing of multi-component pharmaceutical solid systems at supramolecular, particulate, and bulk levels.