Characterization of the Hydrodynamics in the USP Basket Apparatus Using Computational Fluid Dynamics

Abstract

Computational fluid dynamics (CFD) has been extensively used for the USP paddle apparatus II, but limited CFD studies have been conducted on the USP basket apparatus I. We expanded on past CFD basket studies to consider the presence of a tablet inside the basket, compared predictions to in vivo conditions, and confirmed observations around the complexity of nonuniform hydrodynamics. Tablets near the basket perimeter experienced near 5-fold increase in maximum velocity and surface shear stress compared to tablets placed at the center of the basket. At higher basket speeds, the predicted velocities at the center of the basket were closer to in vivo predictions but the surface shear stress was about 2 orders of magnitude lesser. Simulations with a high viscosity fluid (1 Pa-s) showed a 10-fold increase in shear stress on a tablet but a decrease in strain rate compared to low-viscosity medium (0.001 Pa-s) which could impact dissolution rates. Also presented are the insights into turbulent energy dissipation rates that could help in a priori prediction of dissolution rates. Overall, the CFD analysis presented in this work reveals significant differences between the basket and in vivo conditions and will help inform relevant in vitro testing.