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Marin Vatin

Publications and source records attributed to Marin Vatin.

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Optimal Translocation of Living \& Active Filaments in Confinement

Active filament translocation through confined spaces is central to processes ranging from DNA transport through nanopores to cytoskeletal dynamics in cell migration. Here, we use living filamentous \textit{Tubifex tubifex} worms as a model system to investigate how activity and filament conformation govern transport in confinement. By tuning activity via temperature and tracking worm dynamics in a two-chamber geometry connected by a narrow bridge, we quantify their translocation behavior and conformational states. In contrast to passive polymers and filaments, we find that contour length has negligible influence on trapping dynamics, while activity and reorientation jointly control escape. Strikingly, translocation efficiency is maximized at an intermediate temperature ($20^\circ$C), where a balance between directed propulsion and rotational diffusion optimizes exploration. We show that trapping times are governed by the interplay between the timescale of conformational rearrangements and the conformational entropy, quantifying the diversity of accessible shapes. Simulations of tangentially driven active filaments quantitatively reproduce the experimental observations and provide a minimal physical framework to rationalize the existence of an optimal activity. More broadly, our results identify general principles governing active filament transport in confinement, with implications for both biological systems and the design of synthetic active slender objects.

cond-mat.soft

Upsurge of spontaneous knotting in polar diblock active polymers

Spontaneous formation of knots in long polymers at equilibrium is inevitable but becomes rare in sufficiently short chains. Here, we show that knotting and knot complexity increase by orders of magnitude in diblock polymers with a fraction $p$ of self-propelled monomers. Remarkably, this enhancement is not monotonic in $p$ with an optimal value independent of the monomer's activity. By monitoring the knot's size and position we elucidate the mechanisms of its formation, diffusion, and untying and ascribe the non-monotonic behaviour to the competition between the rate of knot formation and the knot's lifetime. These findings suggest a non-equilibrium mechanism to generate entangled filaments at the nano-scale.

cond-mat.soft

Conformation and dynamics of partially active linear polymers

We perform numerical simulations of isolated, partially active polymers, driven out-of-equilibrium by a fraction of their monomers. We show that, if the active beads are all gathered in a contiguous block, the position of the section along the chain determines the conformational and dynamical properties of the system. Notably, one can modulate the diffusion coefficient of the polymer from {active-like to passive-like} just by changing the position of the active block. Further, in special cases, enhancement of diffusion can be achieved by decreasing the overall polymer activity. Our findings may help in the modelization of active biophysical systems, such as filamentous bacteria or worms.

cond-mat.soft