Abstract
Here we develop an injectable composite system based for repeated ultrasound-triggered on-demand drug delivery. An in situ-cross-linking hydrogel maintains model drug (dye)-containing liposomes in close proximity to gas-filled microbubbles that serve to enhance release events induced by ultrasound application. Dye release is tunable by varying the proportions of the liposomal and microbubble components, as well as the duration and intensity of the ultrasound pulses in vitro. Dye is minimal at baseline. The composite shows minimal cytotoxicity in vitro, and benign tissue reaction after subcutaneous injection in rats. Ultrasound application also triggers drug release for two weeks after injection in vivo.