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Modeling the particle shapes and breakage with Rocky DEM

Particulate matter is all around us: in food products, building materials, plastics, chemicals, pharmaceutical powders, and even consumer products. Because of their ubiquity, particulate materials contribute significantly to the economy: They make up a trillion-dollar annual market in the United States.

The pharmaceutical industry, for example, relies extensively on particulate materials, with approximately 90 percent of drug products consisting of solid dosage forms (, 2018), meaning that they are produced from particulate materials.

Small matters, significant gains

That said, it is clear to me that even small gains in particulate material processing could make a significant impact, and not just economically – it can result in better, safer products and processes. But scientists and engineers haven’t had good models for predicting the dynamic behavior of particulate materials.

Fortunately, that is changing with the development of accurate discrete element modeling (DEM) software. At Purdue University, we focus on developing models for predicting how particles flow, mix, break and compact.

We apply these models to improve the performance of industrial processes used to manufacture a wide range of particle-based products, including pharmaceutical tablets.

From my conversations with pharmaceutical companies, I knew that one topic of interest is reducing intra-tablet coating variability. So my team used Rocky DEM to study the question, “Does intra-tablet coating variability get better, does it get worse, or does it stay the same as scale-up occurs?”

Polyhedral elements

We used Rocky DEM because it uses polyhedral elements for modeling the particle shapes and breakage, which are important for predicting the accurate dynamic behavior of a bulk material.

Most other DEM software packages use the more-common bonded-sphere approach, which introduces artificially bumpy surfaces that can significantly affect tablet dynamics.

A GPU-based algorithm was applied to determine the exposure time of each tablet’s surface area elements in a simulated spray. The study concluded that intra-tablet coating variability correlated very well with the angular displacement of tablets as they pass through the spray zone.

The more a tablet tumbles in the coating pan, the better the intra-tablet coating uniformity. You can learn more about the study’s details here.

This finding will give us some ideas on how to improve the overall pharmaceutical coating process – such as agitating tablets just before the spray zone. Our research project was designed to improve the coating process, which in turn can improve overall product quality in the pharmaceutical industry.

Optimizing particulates is key for improving everything from drugs to food to specialty chemicals to biofuels — a challenge that both basic and applied research teams are already attacking.

Carl Wassgreen

Carl Wassgren, Ph.D., is a Professor in the School of Mechanical Engineering and (by courtesy) Department of Industrial and Physical Pharmacy at Purdue University. He is also the Director of Purdue’s Center for Particulate Products and Processes CP3. Wassgren’s research focuses on developing models for predicting the dynamics of particulate systems, including storage, feeding, blending, segregation, dry and wet granulation, tableting, and coating. His work has been applied to the pharmaceutical, agricultural, and biomass industries. Wassgren holds a B.S. from the University of Illinois; his master’s and doctoral degrees are from the California Institute of Technology.

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