Enhancing Small-Molecule Drug Permeability Utilizing a Compact Low-frequency Ultrasonic Transducer

Low-frequency sonophoresis has emerged as a minimally invasive alternative to hypodermic injection for transdermal drug delivery. Ultrasonic cavitation plays a pivotal role in enhancing skin permeability, with the ultrasonic transducer being a central component of this technique. Conventional horn-type transducers are often employed to generate low-frequency, high-intensity ultrasound. However, their bulky and heavy structure imposes substantial limitations for practical medical applications. Therefore, a compact low-frequency ultrasonic transducer capable of inducing cavitation on the skin surface has been designed and developed in this work to overcome these issues. The effect of the developed transducer on skin permeability was evaluated through in vitro sonophoresis experiments using fluorescein sodium as a model compound of low-molecular-weight drugs. The results showed that a 3-minute ultrasound treatment significantly enhanced transdermal permeation, achieving an 80-fold increase compared to the untreated samples. The temperature rise during sonication was limited to 7.1 °C, remaining well within the safety limits. These findings confirmed the potential of the developed compact transducer as a practical tool for safe and efficient sonophoresis-based transdermal drug delivery.