Grid-induced aerosol optimization in pMDIs: A multiscale design, simulation, and experimental study

Conventional pressurized metered dose inhalers (pMDIs) often face challenges in efficiently delivering therapeutic aerosols for the treatment of pulmonary diseases. This study proposes a novel design enhancement: the integration of a grid screen at the outlet of a standard pMDI actuator, supported by a slender 0.8 mm wire. Two grid configurations were developed and tested: (1) a uniform grid with 5 µm pores, and (2) a non-uniform grid where pore diameters increase from 3 µm at the edges to 8 µm at the center. Both configurations were evaluated on straight and curved substrates, maintaining a consistent solidity fraction of 61 %. Spray dynamics were modeled using a coupled computational framework that combines the volume of fluid (VOF) and discrete phase models (DPM). This hybrid approach effectively captures droplet deformation upon impact with the grid screen, followed by their transition into discrete-phase droplets. The trajectories of the resulting droplets were then tracked through a medium-sized mouth-throat (MT) geometry, specifically, the Virginia Commonwealth University (VCU) model, utilizing a particle data transmission method (PDTM). To validate the simulation results, grid screens were fabricated and experimentally tested using a next-generation impactor (NGI) to quantify MT aerosol deposition. Among the four configurations tested, the non-uniform straight grid exhibited the most significant performance improvement. It achieved approximately a 50 % reduction in plume velocity, resulting in lower spray kinetic energy. Additionally, the mass median diameter (MMD) decreased from 3.0 µm to 1.6 µm, attributed to a dual mechanism of mechanical jet disruption and thermally enhanced evaporation. The corresponding reduction in the Weber (We) number indicated a substantial decrease in splash-prone droplets, thereby promoting droplet characteristics that are favorable for deeper lung deposition. Overall, drug delivery efficiency improved by up to 35 %, with a reasonable agreement between computational and experimental results (RMSE = 9.88 %). Furthermore, durability testing under a high-frequency chronic obstructive pulmonary disease (COPD) rescue-use protocol demonstrated stable grid performance for up to three consecutive days, beyond which routine cleaning is recommended to maintain optimal functionality.