Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K01: Chemical Dynamics and Kinetics
3:00 PM–5:36 PM,
Tuesday, March 15, 2022
Room: McCormick Place W-175A
Chair: Siddhartha Akkiraju, Purdue University
Abstract: K01.00011 : Measurements and characterization of the dynamics of tracer particles in an actin network*
5:00 PM–5:12 PM
Presenter:
Golan Bel
(Ben-Gurion University of the Negev)
Authors:
Golan Bel
(Ben-Gurion University of the Negev)
Maayan Levin
(Tel Aviv University)
Yael Roichman
(Tel Aviv University)
The underlying physics governing the diffusion of a tracer particle in a viscoelastic material is a topic of some dispute. The long-term memory in the mechanical response of such materials should induce diffusive motion with a memory kernel, such as fractional Brownian motion (fBM). This is the reason that microrheology is able to provide the shear modulus of polymer networks. Surprisingly, the diffusion of a tracer particle in a network of a purified protein, actin, was found to conform to the continuous time random walk type (CTRW). We set out to resolve this discrepancy by studying the tracer particle diffusion using two different tracer particle sizes, in actin networks of different mesh sizes. We find that the ratio of tracer particle size to the characteristic length scale of a bio-polymer network plays a crucial role in determining the type of diffusion it performs. We find that the diffusion of the tracer particles has features of fBm when the particle is large compared to the mesh size, of normal diffusion when the particle is much smaller than the mesh size, and of the CTRW in between these two limits. Based on our findings, we propose and verify numerically a new model for the motion of the tracer in all regimes. Our model suggests that diffusion in actin networks consists of fBm of the tracer particle coupled with caging events with power-law distributed escape times.
*This work was partially supported by the US-Israel Binational Science Foundation (Grant No. 2014314) and the ISF (Israel Science Foundation) (Grant No. 988/17).
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