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End date: 2024 × Start date: 2020 × DDC: 530 × Publisher: [London] : IOP × WGL Institute: IPF ×

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    Stretching and heating cells with light - Nonlinear photothermal cell rheology
    ([London] : IOP, 2020) Huster, Constantin; Rekhade, Devavrat; Hausch, Adina; Ahmed, Saeed; Hauck, Nicolas; Thiele, Julian; Guck, Jochen; Kroy, Klaus; Cojoc, Gheorghe
    Stretching and heating are everyday experiences for skin and tissue cells. They are also standard procedures to reduce the risk for injuries in physical exercise and to relieve muscle spasms in physiotherapy. Here, we ask which immediate and long-term mechanical effects of such treatments are quantitatively detectable on the level of individual living cells. Combining versatile optical stretcher techniques with a well-tested mathematical model for viscoelastic polymer networks, we investigate the thermomechanical properties of suspended cells with a photothermal rheometric protocol that can disentangle fast transient and slow 'inelastic' components in the nonlinear mechanical response. We find that a certain minimum strength and duration of combined stretching and heating is required to induce long-lived alterations of the mechanical state of the cells, which then respond qualitatively differently to mechanical tests than after weaker/shorter treatments or merely mechanical preconditioning alone. Our results suggest a viable protocol to search for intracellular biomolecular signatures of the mathematically detected dissimilar mechanical response modes. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
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    Correlations in multithermostat Brownian systems with Lorentz force
    ([London] : IOP, 2020) Abdoli, Iman; Kalz, Erik; Vuijk, Hidde D.; Wittmann, René; Sommer, Jens-Uwe; Brader, Joseph M.; Sharma, Abhinav
    We study the motion of a Brownian particle subjected to Lorentz force due to an external magnetic field. Each spatial degree of freedom of the particle is coupled to a different thermostat. We show that the magnetic field results in correlation between different velocity components in the stationary state. Integrating the velocity autocorrelation matrix, we obtain the diffusion matrix that enters the Fokker-Planck equation for the probability density. The eigenvectors of the diffusion matrix do not align with the temperature axes. As a consequence the Brownian particle performs spatially correlated diffusion. We further show that in the presence of an isotropic confining potential, an unusual, flux-free steady state emerges which is characterized by a non-Boltzmann density distribution, which can be rotated by reversing the magnetic field. The nontrivial steady state properties of our system result from the Lorentz force induced coupling of the spatial degrees of freedom which cease to exist in equilibrium corresponding to a single-temperature system. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.