Evaluating 3D-Printed Pre-separator Inserts in a Fast Screening Impactor for Physicochemical Characterization of Fine Particle Dose Release from Dry Powder Inhalers

Abstract

There is growing demand for simplified collection of the fine particle dose (FPD, mass of particles less than 5 µm in diameter) of orally inhaled drug products (OIDPs) for physicochemical characterization. Dissolution kinetics of the FPD are of particular interest in quality control, bioequivalence studies, and the development of branded and generic OIDPs. The Fast Screening Impactor (FSI) is an abbreviated impactor for collecting the FPD of OIDPs, but there is concern that the FSI overrepresents the FPD due to particles larger than the cutoff traveling past the impactor stage.

This issue is most observable when testing dry powder inhalers (DPIs) due to their common use of coarse carrier particles. In this work, we evaluated design modifications to the pre-separator inserts of the FSI to determine their effect on the FPD collection from a commercially available DPI. 3-dimensional (3D) printed FSI inserts were designed to improve impactor cutoff efficiency and collect a FPD equivalent to that collected using full-resolution cascade impactors. Modified FSI inserts were 3D-printed with the nozzle length (T) and baseplate-to-nozzle distance (S) varied while keeping other design parameters, including nozzle diameter (D), the same as the manufacturer’s specifications to determine the impact of design parameters on impactor cutoff efficiency.

We found that increasing the T/D ratio to 1.0 showed little cutoff improvement for the standard pre-separator insert but decreasing the S/D ratio to 1.0 improved the impactor cutoff characteristics of the FPD insert, designed for a 5 µm cutoff at a 60 L/min flowrate. Our improved 3D-printed FPD insert collected an FPD that more closely matched the Anderson Cascade Impactor (ACI) and the Next Generation Impactor (NGI) FPD results. This work evaluated key design parameters necessary for improving the cutoff efficiency of pre-separator inserts to collect FPD more accurately when compared to full-resolution cascade impactors.