Microbubbles have been widely used as ultrasound contrast agents in clinical diagnosis. Moreover, most current preparation methods for microbubbles are uncontrollable, and the as-obtained microbubbles are unstable in aqueous solution or under ultrasound. Here, we report a strategy to prepare superiorly stable microbubbles with three-layer structures by the ethanol–water exchange. This versatile method can also be applied to prepare different kinds of protein microbubbles with various sizes for advanced biomedical applications. To demonstrate this, the protein air microbubbles are created, which is stable in water for several days with intact structures and exhibits excellent contrast-enhanced ultrasound imaging. Moreover, the protein air microbubbles can also deliver a mass of drugs while maintaining their stable structures, making them a platform for ultrasound imaging-guided drug delivery. The versatile protein air microbubbles have great potential for the design and application of theranostic platforms.

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Imaging-guided vascular embolization is frequently performed on patients with advanced hepatocellular carcinoma (HCC) to alleviate symptoms and extend their survival time. However, current operation procedures were not only painful for...

Intravesical instillation is an effective treatment for bladder cancer. However, clinical anticancer agents always suffer rapid excretion by periodic urination, leading to low therapeutic efficacy. Prolonging the retention time of drugs in the bladder is the key challenge for intravesical instillation treatment. Herein, a facile and powerful surface cross‐linking‐freeze drying strategy is proposed to generate ultra‐stable albumin bovine air microbubbles (BSA‐MBs) that can float and adhere to the bladder wall to overcome the excretion of urination and exhibit a remarkable property of long‐term retention in the bladder. More noteworthy, BSA‐MBs are endowed with a specific three‐layer structure, namely, the outer membrane, middle drug loading layer and inner air core, which makes them have a low density to easily float and possess a high drug loading capacity. Based on their unique superiorities, the therapeutic potential of doxorubicin (DOX)‐loaded BSA‐MBs (DOX‐MBs) is exemplified by intravesical instillation for bladder cancer. After injection into the bladder, DOX‐MBs can remain in the bladder for a long time and sustain the release of DOX in urine, exhibiting potent anticancer efficacy. Consequently, the prolonged retention of BSA‐MBs in the bladder renders them as an effective floating drug delivery system for intravesical instillation therapy.