文摘
We design and synthesize monodisperse multi-layer microbubbles (MLBs) with bubble-in-bubble structure using the polymer-backbone-transition method (PBTM). Besides the tunable layer number and microbubble size, we can accurately control the layer-to-layer space and the thickness of each layer. In comparison to traditional single-layer microbubbles, the MLBs can be used as a novel promising model of contrast agent for high-performance ultrasound imaging. The ultrasound signal of MLBs shows a strong structure coupling effect; as the number of layer increases, both the backscatter signal and lifespan increase significantly. We apply a classical acoustic theory to calculate the ultrasound scattering cross-section for the bubbles. It is found that the MLBs exhibit a larger ultrasound scattering cross-section than single-layer bubbles with the same size under certain experimental conditions. Such theoretical results agree well with the ultrasound experimental results.