Characterization of stainless-steel mesh filter material used to capture alveolar doses for in vitro pharmaceutical inhaler testing

The effect of a pharmaceutical aerosol particle in the lung depends on the region in which it lands due to differing physiology between the tracheobronchial (TB) and alveolar regions. Differing airway surface lining depth and composition between the regions will cause the dissolution kinetics to differ as well. Accurate estimation of regional lung doses and dissolution rates is necessary for product development. Recently, an in vitro tool that uses a stainless-steel “TB filter” was developed to fractionate the lung dose into TB and alveolar components. Dissolution of the TB dose can be studied but the use of commercially available hydrophobic filters to collect the alveolar dose may preclude dissolution study of this component. The present study investigates the suitability of tightly woven stainless-steel meshes as an alternative to collect the alveolar dose and enable dissolution analysis. Three grades of stainless-steel mesh were studied. At various representative face velocities, pressure drop across the material was measured with a digital manometer, and particle filtration efficiency was characterized with an electrical low-pressure impactor using a test aerosol of sodium chloride crystals. The resistance to flow was acceptable for all meshes studied; two of three meshes captured more than 90% of particles with aerodynamic diameter ≥1 µm. A two-layer configuration of the meshes captured an alveolar dose comparable to that captured by the commercial filter in proof of concept experiments with a Flovent Diskus dry powder inhaler. This two-layer configuration thus enables studying dissolution of the alveolar dose separate from the TB dose.Copyright © 2026 American Association for Aerosol Research