UTMD-mediated plasmid transfection of HeLa cells. (A) The influence of ultrasound intensity of 0.5 W/cm2, 1.5 W/cm2, and 2.5 W/cm2 on the transfection rate of the miR-21-EGFP plasmid was determined by flow cytometry. (B) The effect of ultrasound intensity of 0.5 W/cm2, 1.5 W/cm2, and 2.5 W/cm2 on the transfection efficiency of miR-21 inhibitor-EGFP plasmid was determined by flow cytometry. The microbubble concentration was 300 μL/mL, the plasmid concentration was 15 μg/mL, the ultrasound duration was 45 s, the ultrasound frequency was 1 MHz, and the load ratio was 20%. UTMD – ultrasound-targeted microbubble destruction; EGFP – enhanced green fluorescent protein.