Regensburg 2025 – scientific programme

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BP: Fachverband Biologische Physik

BP 17: Poster Session II

BP 17.71: Poster

Tuesday, March 18, 2025, 18:00–20:30, P4

Time irreversibility and effective temperature are independently regulated in the actin cortex of living cells — •N Narinder and Elisabeth Fischer-Friedrich — Cluster of Excellence Physics of Life, Technische Universität Dresden, Dresden, Germany

Living cells exhibit non-equilibrium dynamics driven by the intricate interplay between motor activity and their viscoelastic environment. The deviation from thermal equilibrium termed as irreversiblity is commonly characterized by an increased effective temperature and time-reversal symmetry breaking quantified through the Kullback-Leibler divergence (KLD). In this study, we determine entropy production as a measure of irreversibility both by the effective temperature and the KLD in the actin cortex of living cells using atomic force microscopy (AFM) with and without pharmacological treatments that modulate cellular activity and cortical mechanics. Surprisingly, we find that while the entropy production rate consistently increases with effective temperature, its time irreversibility estimated by the KLD can exhibit an opposite trend, depending on the mechanical properties of the cortex. Our findings underpin the role of mechanical properties on the irreversibility. Further, the findings are supported by a minimal model of the AFM tip as probe immersed in the viscoelastic environment of active cell cortex.

Keywords: Active Matter; Viscoelastic Fluids; Non-equililibrium biological systems; Time-irreversibility; Atomic Force Microscopy