Ultrasound-Responsive Polymers: From Controlled Release to Precision Theranostics
Ultrasound-responsive polymers have emerged as a powerful platform for precision medicine by enabling the conversion of external acoustic energy to controlled physicochemical and biological responses. This review summarizes recent advances in the design and application of such systems, highlighting their evolution from passive drug carriers to multifunctional platforms integrating therapy, imaging, and immunomodulation. We first highlight the ultrasound-triggered drug release strategies, including mechanically induced bond cleavage, disruption of noncovalent interactions, and reactive oxygen species (ROS)-mediated degradation, which enable spatiotemporal control over therapeutic delivery. We also discuss sonodynamic therapy, where polymer sonosensitizers generate cytotoxic ROS, representing a shift from indirect drug delivery to a direct therapeutic intervention. Advances in ultrasound and photoacoustic (PA) imaging are further highlighted, emphasizing polymer-enabled improvements in contrast, targeting, and molecular specificity. In particular, long-wavelength PA imaging, molecular structure engineering, and biomarker-activatable probes have significantly enhanced the imaging depth and precision. Finally, we discuss key challenges for clinical translation and outline future directions toward intelligent, self-adaptive systems and closed-loop theranostic platforms. These developments establish ultrasound-responsive polymers as promising foundations for next-generation precision medicine.