Mechanical Profiling of Biopolymer Condensates through Acoustic Trapping

This is the authors' abstract. We don't add key points for this paper.

Characterizing the mechanical properties of single colloids is a central problem in soft matter physics. It also plays a key role in cell biology through biopolymer condensates, which function as membraneless compartments. Such systems can also malfunction, leading to the onset of a number of diseases, including many neurodegenerative diseases; the functional and pathological condensates are commonly differentiated by their mechanical signature. Comprehensive understanding of mechanical properties of biopolymer condensates has, however, remained challenging. In this study, we demonstrate that acoustic trapping can be used to probe the bulk modulus of biopolymer condensates in a contactless manner. We find that acoustic fields exert an acoustic radiation force on condensates, leading to their migration to a trapping point where acoustic potential energy is minimized. Furthermore, our results show that the positional fluctuation of a condensate undergoing Brownian motion in an acoustic potential well can be used as a probe for its bulk modulus. Using this framework, we infer changes in the bulk modulus of polyadenylic acid condensates in response to variations in ionic strength. Our results show that acoustic trapping opens up a path to characterize the bulk modulus of soft colloids in a noninvasive manner with applications in biology, materials science, and beyond.