Stimuli-responsive microcarriers (SRMs) based on multiple emulsions can be widely used in advanced drug delivery, tissue engineering, biosensing, and cell biology. Here a simple and effective compound interface shearing (CIS) method is proposed to one-step produce SRMs for controlled ultrasound (US) activation. In the CIS process, a coaxial needle supplying the core and shell liquids vibrates periodically across a free gas-liquid surface, resulting in the pinch-off of a compound liquid neck for on-demand generation of multiple emulsions. The CIS process is free of confined walls with a pure interface shearing mechanism. Perfectly uniform SRMs with tunable core-shell volume ratios can be produced, following a scaling law of their size as a function of the liquid flow rates and the vibration frequency. US- and magnetic-responsive microcapsules are prepared for magnetic-guided site-targeting delivery, and acid-aided sequential US activation realizes the synergistic delivery of hydrophilic and hydrophobic payloads. It can be concluded that the CIS technique is able to generate multifunctional SRMs at low cost, high uniformity, high flexibility, and effective process control for various fields of potential applications.
Keywords: double emulsion; interface shearing; stimuli-responsive microcarrier; synergistic drug delivery; ultrasound activation.