The bovine serum albumin (BSA)-stabilized IL-4 MDs was fabricated according to previous studies.18 (link),19 (link),100 ng/mL IL-4 (R&D system, China) was used based on a previous study.20 (link) Briefly, 100 ng/mL IL-4, 300 μL perfluorocarbon, and 4 mL of PBS, and 40 mg of bovine serum albumin (BSA, Sigma Aldrich, China) were used for MDs fabrication. The resulting emulsion was ultracentrifuged (Beckman Coulter, Optima XPN-100, USA) at 14,000 rpm for 30 min, and the MDs-IL4 were used for subsequent testing. To generate fluorescence-labeled MDs for fluorescence imaging, fluorescein isothiocyanate (FITC)-labelled BSA (Sigma Aldrich, China) was used for MDs fabrication. Fluorescence-labeled MDs-IL4 were used for MDs characterization using a confocal laser scanning microscopy (CLSM). Briefly, 50 mg MDs-IL4 were diluted into PBS and then observed using a confocal laser scanning microscope with a ×40 objective (Leica DM IRB; Leica, Wetzlar, Germany). MDs-IL4 growth and rupture were observed using an inverted light microscope (Leica, Wetzlar, Germany). Briefly, the samples were exposed to an ultrasound probe with an acoustic frequency 1 MHz by portable home use ultrasound pain therapy device for 25 min (MYCHWAY, China). Images were captured using an inverted light microscope (Leica, Wetzlar, Germany).