Norihiro Oyama (MathAM-OIL, Tohoku University, Japan)

Minimal physical model for cytoplasm as an example of active glass system

Biological cells are highly deformable and cytoplasm inside them is fluidic. However, if we extract the cytoplasm out of a cell, it becomes glassy at the concentration of the living cell cytoplasm [1]. One major difference between these two systems is that living cells contain biological energy source, or ATP. Thanks to ATP, proteins dispersed in cytoplasm inside a living cell can deform "actively". From the view point of active matter physics, such reactions to ATP can be modeled as "non-self-propelled particle (non-SPP) type" active matter. Many efforts have been dedicated to studying glassy dynamics of dense "self-propelled particle" systems and it has already been known that activeness can trigger "active fluidization" in those systems. However, it remains an open question whether similar fluidization takes place even in dense non-SPP systems. In this work, we introduce such non-SPP type ATP activity as a form of time-dependent size change of particles [2,3]. As a result, we have confirmed that active fluidization does take place in this non-SPP model. Moreover, we found that the system shows a re-entrant glass transition when ATP activity effect is strong enough.

[1] K. Nishizawa et al., Sci. Rep. 7, 15143 (2017)
[2] E. Tjhung and L. Berthier, Phys. Rev. E 96, 050601 (2017)
[3] E, Tjhung and T. Kawasaki, Soft Matter 12, 111 (2017)