Reversible increased basement membrane permeability and calcium ion redistribution facilitate ultrasound-enhanced transdermal drug delivery efficiency

Background: Ultrasound-assisted transdermal drug delivery, or sonophoresis, enhances skin permeability, offering a non-invasive alternative for drug administration. However, its clinical application remains limited because of an insufficient understanding of its underlying mechanisms and optimal parameters. This study investigates the factors influencing ultrasound-enhanced drug absorption and examines its biological effects on skin structures and HaCaT cells, providing a comprehensive analysis of its mechanisms.

Methods: In vivo two-photon microscopy was used for real-time visualization of drug penetration in live mice. Ultrasound-induced changes in skin structures were examined using electron microscopy, focusing on alterations in epidermal intercellular junctions and basement membrane structure. Immunofluorescence staining was used to assess keratinocyte adhesion and cytoskeletal changes, while fluorescent calcium probes measured intracellular calcium dynamics in HaCaT cells. Additionally, mechanical stretch experiments were conducted to evaluate cellular responses to mechanical stress after ultrasound exposure.

Results: Ultrasound treatment enhanced drug penetration by inducing structural changes in the epidermis. Ultrasound application altered the basement membrane structure, leading to enlarged pore size and decreased fiber density, which facilitated drug delivery. Nevertheless, these changes were reversible within 2 h after ultrasound treatment. Ultrasound exposure also altered intracellular calcium distribution in HaCaT cells, contributing to changes in cytoskeletal structure and cell adhesion. Furthermore, ultrasound-treated cells exhibited reduced resistance to external mechanical stress. These findings suggested that ultrasound could promote drug delivery by changing skin structures, modulating calcium ion distribution, and altering cell adhesion and morphology.

Conclusions: Our study provides novel insights into the mechanisms of ultrasound-enhanced transdermal drug delivery, including real-time in vivo observations of drug penetration and the reversible effects on skin structure. These findings provide a better understanding of ultrasound's potential for safe and effective drug delivery, contributing to its future clinical applications.

HaCaT cells; Sonophoresis; Transdermal drug absorption; Ultrasonic transdermal delivery; Ultrasound.