(W1130-09-59) Predicting Tablet Cascade of ConsiGma Continuous Coater Using Discrete-Element-Method (DEM) Simulations

Purpose: Coating is an important process during tablet development, serving multiple purposes including modifying drug release, moisture/light protection, taste masking, and increasing the aesthetic value of the drug.¹ Unlike traditional pan coaters, the ConsiGma^TM coater uses lower pan loads at high pan speeds and air knives to entrain tablets in a cascading movement, thereby improving the efficiency and product quality.² Predictive technologies such as modeling with Discrete Element Method (DEM) can alleviate the high-cost trial-and-error methodologies used when determining drug product formulations and manufacturing processes for solid oral-dosage formulations.³ Developing a validated DEM model of the tablet cascade will enable process parameter decisions without having to expend the labor and possible waste of drug product. This study involves using DEM and Computational Fluid Dynamics (CFD) to simulate the tablet movements during the continuous coating process for optimizing development and enhancing process understanding

Methods: Placebo tablets were compressed, and the tablet cascading study was conducted at GEA Process Engineering Inc., Maryland. Tablets were compressed at three different weights (244 mg, 488 mg, 680 mg) targeting hardnesses to avoid chipping during the cascading process. The cascading study was conducted using a 2³ factorial design with two center points (12 runs, randomized) to identify the impact of the varied parameters of pan load, pan speed and air-knife pressure acting on the tablet motion. Videos of these cascading runs were captured using a GoPro camera and analyzed using Tracker video analysis. Cascading was quantified by measuring the distance between the center of the coater and tablet bed, defined as cord length, at various angles on the cascading motion of the tablets in the rotating drum. Rocky DEM was used to create a DEM – CFD coupled model of tablet motion in the ConsiGma® Coater. Simulations were conducted to computationally model various parameters for the 680 mg tablet image cascade, generating 60 seconds of steady-state tablet cascade for post-processing of the resulting data and comparison to the video analysis.

Results: The angle observed to best represent the tablet cascading motion and for comparing the resulting cord lengths to the process parameters is found to be at negative 45° from the vertical axis, which is roughly located at the center of the tablet cascade. The longer the cord length at any given angle, the further the tablets would be from the positioning of ConsiGma® Coater spray nozzle. Statistical analysis of the cascading study results shows that the pan speed had a significant impact on the cord length at negative 45°, where the higher pan speed resulted in higher cord length. A DEM – CFD coupled model of tablet motion in the ConsiGma® Coater was necessary to capture dynamic motion of the tablets and air acting on the environment through the pressurized air-nozzles. DEM simulated cord lengths for 680 mg tablet showed similar averages to the cascading study. The resulting cord length data from the DEM simulations support the determined trends in tablet motion found from the experimental cascade study for the 680 mg tablet image. Ongoing work includes validation of the motion of the cascade across the 680 mg tablets with these resulting cord lengths and further analysis of tablet velocity and impacts on the tablets. These efforts will help generate a fundamental understanding of the physical interactions in the ConsiGma® coater.

Conclusion: Trends found in tablet motion during the experimental cascade study of the 680 mg tablet image are supported by the resulting cord lengths data from DEM simulations; ensuring the accuracy and application of cord lengths to be a representative measurement to encompass tablet motion. Future work includes simulating tablet cascades for 244 mg and 488 mg tablet images, along with implementation of further refinements to best simulate tablet motion in the ConsiGma® coaters. Specifically, calibration of tablet-to-tablet and tablet-to-wall coefficient of restitutions (COR) and more specific coefficients of frictions to be implemented on the model. With this refinement, we aim to capture accurate motion and variability found during cascading.

References: 1. Seo, K. S., et al. (2020). Pharmaceutical Application of Tablet Film Coating. Pharmaceutics, 12, 9.
2. Kept, C. I. et al. (2019). Modeling, experimental trials, and design space determination for the GEA ConsiGma™ coater. Drying Technology, 37, 4.
3. Boehling, P., et al. (2021). Validating a Numerical Simulation of the ConsiGma® Coater. AAPS PharmSciTech, 22, 10.