Ultrasound has recently been used in transdermal and gene delivery, but its usage in intrascleral delivery was just discovered by our group. Ultrasound-mediated intrascleral drug delivery offers a novel alternative for treating posterior eye diseases including age-related macular degeneration. However, the effectiveness of this new technology is still far from application. This project is a continuation of our previous findings on ultrasound-mediated intrascleral drug delivery, aiming to maximize the effectiveness of this technology. We hypothesized that the enhancement in intrascleral protein penetration by ultrasound was related to cavitation effect. Ex vivo diffusion cell experiments using rabbit sclera were done using ultrasound with different mechanical index and frequencies (40 kH...[ Read more ]

Ultrasound has recently been used in transdermal and gene delivery, but its usage in intrascleral delivery was just discovered by our group. Ultrasound-mediated intrascleral drug delivery offers a novel alternative for treating posterior eye diseases including age-related macular degeneration. However, the effectiveness of this new technology is still far from application. This project is a continuation of our previous findings on ultrasound-mediated intrascleral drug delivery, aiming to maximize the effectiveness of this technology. We hypothesized that the enhancement in intrascleral protein penetration by ultrasound was related to cavitation effect. Ex vivo diffusion cell experiments using rabbit sclera were done using ultrasound with different mechanical index and frequencies (40 kHz - 1 MHz). The dependence of the enhancement by ultrasound to cavitation type was also examined. Results showed that intrascleral protein penetration increases with mechanical index (MI) in stable cavitation range, while decreases when MI reaches transition range and transient cavitation range, suggesting stable cavitation is one of the major possible mechanisms for the enhancement by ultrasound. Next, in order to maximize stable cavitation effect, microbubbles were added to the ultrasound radiating medium. With microbubbles addition, penetration of albumin increased up to 53%, showed that microbubbles addition can improve the effect of ultrasound-mediated intrascleral drug delivery. After that, the effectiveness of ultrasound-mediated transscleral drug delivery was examined in vivo using 40 kHz ultrasound under stable cavitation. FITC-dextran concentration in vitreous was examined, and 0.039 μg FITC-dextran/g vitreous was found, compare to no detectable FITC-dextran in the control. Effect of repeated ultrasound application was examined. A 40-fold increase was found in repeated application setup. Reversibility of the barrier function of sclera was investigated, ex vivo sclera recovery test suggested that sclera needs 48 hours after the ultrasound application to recover, while for in vivo, transscleral protein penetration significantly reduced after 7 days.