Living Matter: Mesoscopic Active Materials

Abstract

An introduction to the physical properties of living active matter at the mesoscopic scale (tens of nanometers to micrometers) and their unique features compared with "dead," nonactive matter is presented. This field of research is increasingly denoted as "biological physics" where physics includes chemical physics, soft matter physics, hydrodynamics, mechanics, and the related engineering sciences. The focus is on the emergent properties of these systems and their collective behavior, which results in active self-organization and how they relate to cellular-level biological function. These include locomotion (cell motility and migration) forces that give rise to cell division, the growth and form of cellular assemblies in development, the beating of heart cells, and the effects of mechanical perturbations such as shear flow (in the bloodstream) or adhesion to other cells or tissues. An introduction to the fundamental concepts and theory with selected experimental examples related to the authors' own research is presented, including red-blood-cell membrane fluctuations, motion of the nucleus within an egg cell, self-contracting acto-myosin gels, and structure and beating of heart cells (cardiomyocytes), including how they can be driven by an oscillating, mechanical probe.

Dynamics and escape of active particles in a harmonic trap

“…In addition, we have the active force correlation time, τ on (the single source and N source implementations of the active force also have a mean period τ tot ≡ τ on + τ of f ). If one considers a finite trap, namely the trapping potential is truncated at a certain point, x esc , which if passed by the particle it escapes and its dynamics is not described by the above equations anymore, an additional relevant time scale is the thermal mean escape time, approximated by Kramers' formula, τ thermal esc = τ 0 e ∆E(xesc)/kB T , (4) where ∆E(x esc ) is the energy difference between the escape point and the bottom of the potential well, and τ 0 is a coefficient with units of time [41][42][43] (see Appendix D for more details). In order to simulate the dynamics of the particles, we used the non-dimensional version of eq.…”

“…In order to investigate the relevance of our results to other confining potentials, we simulated the escape dynamics of particles subjected to thermal and active noise confined by two non-harmonic potentials. The first is the V-shaped potential, 4 . The dynamics is described by eq.…”

Network Organisation and the Dynamics of Tubules in the Endoplasmic Reticulum

“…The tubules of the endoplasmic reticulum provide a novel example of driven active polymeric systems that can be compared with more standard systems, such as myosin with actin networks or kinesins with microtubule networks (29)(30)(31)(32). A unique feature of the ER is its ability to experience large geometrical and morphological changes due to the elasticity of the lipid tubules e.g.…”

Enforcing shaping of thin gel sheets by anisotropic swelling

“…So, swelling and growth are quite different phenomena from an energetic point of view, especially when they come together (i.e. in active gels [4,2]). There is a clear distinction between them and a full modeling of their interactions is fundamentally important to accurately describe the combined processes [8].…”