Localized delivery of compounds into articular cartilage by using high-intensity focused ultrasound

Localized delivery of drugs into an osteoarthritic cartilaginous lesion does not yet exist, which limits pharmaceutical management of osteoarthritis (OA). High-intensity focused ultrasound (HIFU) provides a means to actuate matter from a distance in a non-destructive way. In this study, we aimed to deliver methylene blue locally into bovine articular cartilage in vitro. HIFU-treated samples (n = 10) were immersed in a methylene blue (MB) solution during sonication (f = 2.16 MHz, peak-positive-pressure = 3.5 MPa, mechanical index = 1.8, pulse repetition frequency = 3.0 kHz, cycles per burst: 50, duty cycle: 7%). Adjacent control 1 tissue (n = 10) was first pre-treated with HIFU followed by immersion into MB; adjacent control 2 tissue (n = 10) was immersed in MB without ultrasound exposure. The MB content was higher (p < 0.05) in HIFU-treated samples all the way to a depth of 600 µm from AC surface when compared to controls. Chondrocyte viability and RNA expression levels associated with cartilage degeneration were not different in HIFU-treated samples when compared to controls (p > 0.05). To conclude, HIFU delivers molecules into articular cartilage without major short-term concerns about safety. The method is a candidate for a future approach for managing OA.