title: 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.
authors.affiliation: Université de Toulouse, INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Allés Camille Soula, 31400 Toulouse, France CNRS, IMFT, 31400 Toulouse, France.
authors.forename: Adama
authors.initials: A
authors.lastname: Creppy
authors.affiliation: Université de Toulouse, INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Allés Camille Soula, 31400 Toulouse, France CNRS, IMFT, 31400 Toulouse, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Plouraboué
authors.affiliation: Université de Toulouse, INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Allés Camille Soula, 31400 Toulouse, France CNRS, IMFT, 31400 Toulouse, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Praud
authors.affiliation: INRA, CNRS, UMR, 37380 Nouzilly, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Druart
authors.affiliation: Université de Toulouse, INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Allés Camille Soula, 31400 Toulouse, France CNRS, IMFT, 31400 Toulouse, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Cazin
authors.affiliation: CNRS, Institut de Mathématiques de Toulouse UMR 5219, 31062 Toulouse, France.
authors.forename: Hui
authors.initials: H
authors.lastname: Yu
authors.affiliation: Department of Mathematics, Imperial College London, London SW7 2AZ, UK pdegond@imperial.ac.uk.
authors.forename: Pierre
authors.identifier: 0000-0002-4886-6968
authors.initials: P
authors.lastname: Degond
mesh_terms: D000818:Animals; D057446:Hydrodynamics; D056656:Lab-On-A-Chip Devices; D008297:Male; D008954:Models, Biological; D012756:Sheep; D013094:Spermatozoa / Q000166:cytology / Q000502:physiology*
keywords: Vicsek model; active fluids; self-organized hydrodynamics; semen quality