Suspension formulations for inhalation therapy can have the benefit of prolonged retention time in the lung and may allow controlled release of the drugs to treat lung disorders.

However, delivery of suspensions is often complicated due to incompatibility of the inhaler system with suspension particle size (e.g. Mesh nebulisers) or unwanted particle interactions as the result of the aerosolisation mechanism (Ultrasound nebulisers). In this study the nebulisation of suspension formulations using a surface acoustic wave (SAW) device with liquid confining microstructure was investigated.

We demonstrated the nebulisation of monodisperse suspensions with particle sizes from 4.8 µm to 0.1 µm and identified key factors that when adjusted improve aerosolisation. We found that particle dispersity is influenced by acoustic energy transmission into the liquid dispensing system and liquid confining microstructure. Acoustic cavity effects drive particle aggregation for larger particles.

This resulted in poor delivery of suspensions into the Andersen Cascade Impactor. Controlled liquid introduction of suspension formulations to the SAW transducer improved the delivery of larger particles by 250%.