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Traditional implanted drug delivery systems cannot easily change their release profile in real time to respond to physiological changes. Here we present a microfluidic aqueous two‐phase system to generate microcapsules that can release drugs on demand as triggered by focused ultrasound (FUS). The biphasic microcapsules are made of hydrogels with an outer phase of mixed molecular weight (MW) poly(ethylene glycol) diacrylate that mitigates premature payload release and an inner phase of high MW dextran with payload that breaks down in response to FUS. Compound release from microcapsules could be triggered as desired; 0.4 μg of payload was released across 16 on‐demand steps over days. We detected broadband acoustic signals amidst low heating, suggesting inertial cavitation as a key mechanism for payload release. Overall, FUS‐responsive microcapsules are a biocompatible and wirelessly triggerable structure for on‐demand drug delivery over days to weeks. [ABSTRACT FROM AUTHOR]

A frequency‐domain, non‐contact approach to photoacoustic microscopy (PAM) that employs amplitude‐modulated (0.1–1 MHz) laser for excitation (638‐nm pump) in conjunction with a 2‐wave mixing interferometer (532‐nm probe) for non‐contact detection of photoacoustic waves at the specimen surface is presented. A lock‐in amplifier is employed to detect the photoacoustic signal. Illustrative images of tissue‐mimicking phantoms, red‐blood cells and retinal vasculature are presented. Single‐frequency modulation of the pump beam directly provides an image that is equivalent to the 2‐dimensional projection of the image volume. Targets located superficially produce phase modulations in the surface‐reflected probe beam due to surface vibrations as well as direct intensity modulation in the backscattered probe light due to local changes in pressure and/or temperature. In comparison, the observed modulations in the probe beam due to targets located deeper in the specimen, for example, beyond the ballistic photon regime, predominantly consist of phase modulation. [ABSTRACT FROM AUTHOR]