Size-Dependent Nonlinear Acoustic Responses and Stable Cavitation of Polymeric Microbubbles

Polymeric microbubbles (MBs) are increasingly being explored as contrast agents for ultrasound (US) imaging and as carriers for US-mediated therapies. Many of these applications benefit from MBs that exhibit strong nonlinear acoustic responses and robust cavitation capabilities. Although structural features, such as size, are known to influence the overall acoustic behavior of MBs, their specific impact on nonlinear responses and cavitation dynamics remains poorly understood and characterized. In this study, we investigated the size-dependent acoustic properties of poly(butyl cyanoacrylate) (PBCA) MBs. Our results show that larger PBCA MBs produce stronger acoustic signals and more pronounced nonlinear responses, including second harmonic generation, whereas smaller PBCA MBs exhibit greater acoustic stability and a higher capacity to sustain stable cavitation. These findings elucidate the role of size in shaping the acoustic behavior of polymeric MBs in a quantitative manner and may inform the design of new agents for enhanced US imaging and US-mediated therapies.