Symmetry-breaking phase transitions in highly concentrated semen

Abstract

New experimental evidence of self-motion of a confined active suspension is presented. Depositing fresh semen sample in an annular shaped microfluidic chip leads to a spontaneous vortex state of the fluid at sufficiently large sperm concentration. The rotation occurs unpredictably clockwise or counterclockwise and is robust and stable. Furthermore, for highly active and concentrated semen, richer dynamics can occur such as self-sustained or damped rotation oscillations. Experimental results obtained with systematic dilution provide a clear evidence of a phase transition towards collective motion associated with local alignment of spermatozoa akin to the Vicsek model. A macroscopic theory based on previously derived self-organized hydrodynamics models is adapted to this context and provides predictions consistent with the observed stationary motion.

Geometric control of active collective motion

“…Upon increasing channel width, flow patterns start exhibiting longitudinal oscillations leading to sinusoidal trajectories and eventually take the form of arrays of counter-rotating vortices. Longitudinal density waves were also reported in the case of dense semen [43]. The observed transition to directed motion has been predicted in a number of models for active nematics [44,45], where extensile stresses were found to be the destabilizing factor leading to spontaneous flows.…”

“…The case of periodic geometries such as circular channels and racetracks has also been studied, where spontaneous flows have been reported in both bacterial [42] and sperm [43] suspensions above a critical density. In the case of bacteria, Wioland et al [42] systematically studied the effect of geometry by varying the channel width.…”

Magnetotactic bacteria in a droplet self-assemble into a rotary motor

“…Like the many artificial active systems recently proposed to tackle this question [11][12][13][14][15], assemblies of motile bacteria turned out to be a rich and insightful experimental playground [16][17][18][19][20][21][22][23]. Among the rich topics that were investigated, the confinement of bacteria and of active particles has been the focus of many experimental [24][25][26][27] and theoretical studies [27,28], showing that, under strong confinement, vortical collective motions may spontaneously appear.…”

Nonequilibrium fluctuations during diffusion in liquid layers

“…Examples include monolayers made of liquid crystals [35] and lipid bilayers [36]. Indeed, 2D hydrodynamics is becoming an increasingly important tool to describe the spatial-temporal dynamics of active matter in 2D to describe phenomena such as the swarming of epithelial cell monolayers [37], the development of turbulence in concentrated living sperm [38,39], and the collective dynamics of swimming bacteria [40].…”