Discrete Element Method Evaluation of Triboelectric Charging Due to Powder Handling in the Capsule of a DPI

Abstract

The generation and accumulation of an electrostatic charge from handling pharmaceutical powders is a well-known phenomenon, given the insulating nature of most APIs (Active Pharmaceutical Ingredients) and excipients. In capsule-based DPIs (Dry Powder Inhalers), the formulation is stored in a gelatine capsule placed in the inhaler just before inhalation. The action of capsule filling, as well as tumbling or vibration effects during the capsule life cycle, implies a consistent amount of particle–particle and particle–wall contacts. A significant contact-induced electrostatic charging can then take place, potentially affecting the inhaler’s efficiency. DEM (Discrete Element Method) simulations were performed on a carrier-based DPI formulation (salbutamol–lactose) to evaluate such effects. After performing a comparison with the experimental data on a carrier-only system under similar conditions, a detailed analysis was conducted on two carrier–API configurations with different API loadings per carrier particle. The charge acquired by the two solid phases was tracked in both the initial particle settling and the capsule shaking process. Alternating positive–negative charging was observed. Particle charging was then investigated in relation to the collision statistics, tracking the particle–particle and particle–wall events for the carrier and API. Finally, an analysis of the relative importance of electrostatic, cohesive/adhesive, and inertial forces allowed the importance of each term in determining the trajectory of the powder particles to be estimated.

A thick wall concept for robust treatment of contacts in DEM simulation of highly polydisperse particulate systems

“…Frontiers in Chemical Engineering frontiersin.org pharmaceutical interest in an inhaler capsule during a simulated inhalation cycle. The computational model and simulation conditions details are available in (Alfano et al, 2022c;Alfano et al, 2023) and a brief summary is reported below.…”

“…The DEM implementation available in the MFiX code, version 18.1.5 (Garg et al, 2012), as modified by our group as detailed in Alfano et al (2021b); Alfano et al (2022c); Alfano et al (2023), is adopted. The original open-source MFiX-DEM code has been extended to include the CDT rolling friction model, the JKR elastic-cohesive model including attractive forces also for negative overlaps upon detachment, all the fictitious forces discussed above and the implementation of the proposed thick wall concept, by means of Eqs.…”

“…The capsule is depicted in Figure 9 with its sizes and its resting position in a DPI. It represents the same system studied in our previous works (Alfano et al, 2022c;Alfano et al, 2023). The capsule rotates with a constant angular acceleration of 887 rad/s 2 , starting from rest.…”