title: Flagellar kinematics and swimming of algal cells in viscoelastic fluids.
abstract: The motility of microorganisms is influenced greatly by their hydrodynamic interactions with the fluidic environment they inhabit. We show by direct experimental observation of the bi-flagellated alga Chlamydomonas reinhardtii that fluid elasticity and viscosity strongly influence the beating pattern - the gait - and thereby control the propulsion speed. The beating frequency and the wave speed characterizing the cyclical bending are both enhanced by fluid elasticity. Despite these enhancements, the net swimming speed of the alga is hindered for fluids that are sufficiently elastic. The origin of this complex response lies in the interplay between the elasticity-induced changes in the spatial and temporal aspects of the flagellar cycle and the buildup and subsequent relaxation of elastic stresses during the power and recovery strokes.
authors.affiliation: Department of Mechanical Engineering &Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: B
authors.initials: B
authors.lastname: Qin
authors.affiliation: 1] Department of Mechanical Engineering &Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104 [2] Department of Physics &Astronomy, Haverford College, Haverford, PA 19041.
authors.forename: A
authors.initials: A
authors.lastname: Gopinath
authors.affiliation: 1] Department of Mechanical Engineering &Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104 [2] Department of Physics &Astronomy, Haverford College, Haverford, PA 19041.
authors.forename: J
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Physics &Astronomy, Haverford College, Haverford, PA 19041.
authors.forename: J P
authors.initials: JP
authors.lastname: Gollub
authors.affiliation: Department of Mechanical Engineering &Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: P E
authors.initials: PE
authors.lastname: Arratia
mesh_terms: D001696:Biomechanical Phenomena; D016825:Chlamydomonas reinhardtii / Q000502:physiology*; D005407:Flagella / Q000502:physiology*; D008954:Models, Biological