Effectiveness of 3 MHz ultrasound in ex vivo scleral delivery of macromolecules of different sizes

Therapeutic ultrasound offers a novel approach for enhancing scleral delivery of macromolecules for treatment of various ocular diseases. Our previous in vitro diffusion cell studies showed that 3 MHz ultrasound could enhance scleral delivery of Avastin (MW: 149 kDa). We tested similar ultrasound parameters in an ex vivo whole eye rabbit model by using fluorescently labeled FITC-dextran of various sizes (40, 70, and 150 kDa) to mimic the sizes of the current macromolecules drugs for treatment of retinopathies. 3 MHz ultrasound was applied for 5 min on the sclera of the eye submersed in a macromolecule solution, and then the eyes were left in the solution for another 55 min while in the 34.6 °C water bath. Ultrasound was not turned on for the sham-treated group. Temperature modeling was performed to assess the safety of 5-min ultrasound application in the eye. The fluorescence intensity values of FITC-150 group were statistically different (p < 0.05) between the ultrasound-treated (1809.4, n = 8) and their sham-treated group (1185.8, n = 8). However, the FITC-70 and -50 groups lacked any appreciable difference between their ultrasound-treated (1313.6, n = 8) and (1646.3, n = 6), and their sham-treated groups (1431, n = 8) and (1121.8, n = 6), respectively. Thermal simulations demonstrated a temperature rise of 4.6 °C, while experimentally the maximum temperatures was 4.4 °C.