Electrostatics of pharmaceutical inhalation aerosols

Abstract

Objectives This review focuses on the key findings and developments in the rapidly expanding research area of pharmaceutical aerosol electrostatics. Key findings Data from limited in-vivo and computational studies suggest that charges may potentially affect particle deposition in the airways. Charging occurs naturally in the absence of electric fields through triboelectrification, that is contact or friction for solids and flowing or spraying for liquids. Thus, particles and droplets emitted from pulmonary drug delivery devices (dry powder inhalers, metered dose inhalers with or without spacers, and nebulisers) are inherently charged. Apparatus with various operation principles have been employed in the measurement of pharmaceutical charges. Aerosol charges are dependent on many physicochemical parameters, such as formulation composition, device construction, relative humidity and solid-state properties. In some devices, electrification has been purposefully applied to facilitate powder dispersion and liquid atomisation. Summary Currently, there are no regulatory requirements on characterising electrostatic properties of inhalation aerosols. As research in this area progresses, the new knowledge gained may become valuable for the development and regulation of inhalation aerosol products.

Development and Comparison of New High-Efficiency Dry Powder Inhalers for Carrier-Free Formulations

“…Similarly, powder deposition on the walls of the CC can potentially be dislodged easier from capsule‐wall impactions when PTFE coating is used. Considering electrostatic forces, triboelectric charging is known to occur with pharmaceutical powders and is reduced when surfaces of the same material are separated compared with surfaces of different materials . Therefore, coating both the capsule and CC with the same low surface energy material can reduce the buildup of electrostatic charge, which reduces an additional powder retention mechanism and allows the capsule to move more freely in the chamber.…”

Deposition Mechanisms

“…Although human airways are normally neutral, image charges with equal magnitude and opposite polarity to charged particles may be induced on the surfaces, especially inside small airways in the peripheral lung. (13) Yu (14) derived formulae for deposition fraction due to mutual repulsion in a cylindrical tube as follows:…”

“…Disruption of the electrical double layer in liquid surfaces during atomization also generates spontaneously charged droplets. (13) Particle charges are dependent on many physicochemical parameters, such as formulation composition, device construction, relative humidity, and solid-state properties. This topic is further discussed in the section on particle characteristics.…”

Effect of Induced Charge on Deposition of Uniformly Charged Particles in a Pediatric Oral-Extrathoracic Airway

“…Electrostatic charge measurements for pharmaceutical inhalers have revealed high charge levels on the particles emitted from some commercial respiratory drug delivery devices (Byron et al 1997;Kwok et al 2005;Hoe et al 2009;Kwok and Chan 2009). Kwok et al (2005) reported charge levels higher than 40,000 e per particle for particles generated by a commercial metered dose inhaler (MDI).…”