Ultrasonic nebulization platforms for pulmonary drug delivery

Importance of the field: Since the 1950s, ultrasonic nebulizers have played an important role in pulmonary drug delivery. As the process in which aerosol droplets are generated is independent and does not require breath-actuation, ultrasonic nebulizers, in principle, offer the potential for instantaneously fine-tuning the dose administered to the specific requirements of a patient, taking into account the patient's breathing pattern, physiological profile and disease state. Nevertheless, owing to the difficulties and limitations associated with conventional designs and technologies, ultrasonic nebulizers have never been widely adopted, and have in recent years been in a state of decline. Areas covered in this review: An overview is provided on the advances in new miniature ultrasonic nebulization platforms in which large increases in lung dose efficiency have been reported. What the reader will gain: In addition to a discussion of the underlying mechanisms governing ultrasonic nebulization, in which there appears to be widely differing views, the advantages and shortcomings of conventional ultrasonic nebulization technology are reviewed and advanced state-of-the-art technologies that have been developed recently are discussed. Take home message: Recent advances in ultrasonic nebulization technology demonstrate significant potential for the development of smart, portable inhalation therapy platforms for the future. Nevertheless, there remain considerable challenges that need to be addressed before such personalized delivery systems can be realized. These have to be addressed across the spectrum from fundamental physics through to in vivo device testing and dealing with the relevant regulatory framework.