A Q&A with Jamie Clayton of Freeman Technology
What is dynamic powder testing and why is it valuable for DPI development?
Dynamic powder testing is a modern technique developed specifically to generate process relevant powder properties where dynamic powder properties, including basic flowability energy (BFE) and specific energy (SE), are generated from measurements of the axial and rotational forces acting on a blade as it rotates through the powder sample (Figure 1).
BFE, which is measured with a downward traverse of the blade that forces the powder down against the base of the test vessel, quantifies confined flow behavior and has been securely correlated with, for example, performance in vacuum drum filling applications. SE is measured with an upward traverse and characterizes unconfined flow behavior, such as that observed during gravity filling.
Compared with the USP methods of measuring powders, dynamic testing more reliably differentiates closely similar samples while measuring properties that correlate with inhaler performance, which makes it the most valuable approach for DPI formulations that we have seen. Dynamic testing is more repeatable, reproducible, and sensitive than the USP methods, and test conditions can be selected to directly simulate the application of interest.
Powder behavior is highly dependent on the conditions to which the powder is subjected – for example, think of how aeration or consolidation transform flowability. Therefore, to optimize a DPI formulation, we need to characterize behavior across a range of conditions. To fully characterize a DPI formulation, we need to consider the powder’s behavior in a low stress state, the impact of compression on the powder, and the formulation’s aeration performance.
During manufacture, for example, good flowability aids precise volumetric dosing from a bulk quantity of formulation. Technologies used for this task include dosing plate and tamping pin, dosator and pin, and vacuum drum filling, each of which requires powder to flow into a confined volume, typically in a low stress regime subject only to gravitational forces. Then, consolidation of the extracted dose, either by compaction or the application of vacuum, ensures consistent bulk density and forms a stable plug that can be transferred to packaging.
