Multivariate Approaches for Powder Characterization

John Yin, an applications specialist with Freeman Technology, discusses the importance of powder-characterization techniques for optimizing pharmaceutical product development and manufacturing processes.

Q. Why is powder characterization so important for the pharmaceutical industry? A. Understanding and characterizing powder behavior is critical for the production of solid-dosage formulations, and there are many key properties of powders that determine how they will behave in a hopper, when being filled into a die, and compressed into a tablet. Understanding the variables and processing conditions involved in relation to what powders are required to do, therefore, is relevant during all aspects of development and manufacturing and can provide information that can be used for formulation development, process optimization, and improvement of the quality of the final drug product.

Q. What advances in powder characterization have been achieved in recent years? A. In the past, much of the focus on powder characterization has been at the single aspect level where one standard or number is expected to dictate ‘good’ or ‘bad’ once and for all. In reality, we rely on multiple techniques for explaining behavioral differences when being subjected to many processing conditions. While some information can be obtained with traditional methods, such as bulk-tapped density, flow through an orifice, and angle of repose, these techniques are not at all representative of the conditions that powders see under process conditions and, therefore, are not able to provide process-relevant and differentiating information given the process technologies in use today in the pharmaceutical industry.

The multivariate approach for characterizing powders has made it possible to gain much greater insights into how the combination of powder physical properties and external variables affect their behavior. Dynamic testing for example, which measures the flow energy of a powder with respect to external conditions, such as aeration, flow rate, and consolidation, is a newer technique enjoying considerable industrial uptake. Advances in shear testing are also improving both the precision and reproducibility of this important analytical method.

Q. What limitations remain with respect to powder-characterization technology for the pharma industry? Why are these issues important?A. One of the biggest limitations at this point is the lack of understanding of powder behavior at the level needed to describe such behavior mathematically or from an axiom perspective. There are so many variables, not just particle size and density, which are often perceived as the only critical factors that influence powder behavior, but also the surface texture, particle shape, stiffness, and porosity as well as external influences, such as air, moisture, consolidation stress, and flow rate, which can all contribute to the picture. There is much work to be done in this area and it will be a steep learning curve. A second challenge is the need to make the pharmaceutical industry and other powder-processing industries (that share similar challenges) aware of the benefits of more comprehensive powder characterization.

Q. What advances in powder-characterization technology might be expected? A. The adoption of continuous manufacturing for the production of solid dosage forms will have an impact on powder-characterization technology. In addition, as the amount of data gathered on different powder systems increases, we will continue to gain more knowledge about powder properties and behavior and be able to expand our insight into performance with respect to different processing conditions.