Bifunctional ultraviolet/ultrasound responsive composite TiO₂/polyelectrolyte microcapsules

Designing and fabricating multifunctional microcapsules are of considerable interest in both academic and industrial research aspects. This work reports an innovative approach to fabricate composite capsules with high UV and ultrasound responsive functionalities that can be used as external triggers for controlled release, yet with enhanced mechanical strength that can make them survive in a harsh environment. Needle-like TiO₂ nanoparticles (NPs) were produced in situ into layer-by-layer (LbL) polyelectrolyte (PE) shells through the hydrolysis of titanium butoxide (TIBO). These rigid TiO₂ NPs yielded the formed capsules with excellent mechanical strength, showing a free standing structure. A possible mechanism is proposed for the special morphology formation of the TiO₂ NPs and their reinforcing effects. Synergistically, their response to UV and ultrasound was visualized via SEM, with the results showing an irreversible shell rapture upon exposure to either UV or ultrasound irradiation. As expected, the release studies revealed that the dextran release from the TiO₂/PE capsules was both UV-dependent and ultrasound-dependent. Besides, the biocompatibility of the capsules with the incorporation of amorphous TiO₂ NPs was confirmed by an MTT assay experiment. All these pieces of evidence suggested a considerable potential medicinal application of TiO₂/PE capsules for controlled drug delivery.