Browsing by Author "Jana, Saikat"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Effect of boundaries on swimming of Paramecium multimicronucleatum
    Jana, Saikat (Virginia Tech, 2013-09-03)
    Microorganisms swimming in their natural habitat interact with debris and boundaries, which can modify their swimming characteristics. However, the boundary effect on swimming microorganisms have not been completely understood yet, and is one of most active areas of research. Amongst microorganisms, unicellular ciliates are the fastest swimmers and also respond to a variety of external cues. We choose Paramecium multimicronucleatum as a model system to understand the locomotion of ciliates. First, we explore the effects of boundaries on swimming modes of Paramecium multimicronu- cleatum by introducing them in 2D films and 1D channels. The geometric confinements cause the Paramecia to transition between: a directed, a meandering and a self-bending behaviors. During the self-bending mode the cell body exerts forces on the walls; which is quantified by using a beam bending analogy and measuring the elasticity of the cell body. The first inves- tigation reveals the complicated swimming patterns of Paramecium caused by boundaries. In the second study we investigate the directed swimming of Paramecium in cylindrical capillaries, which mimics the swimming of ciliates in the pores of soil. A finite-sized cell lo- comoting in extreme confinements creates a pressure gradient across its ends. By developing a modified envelop model incorporating the confinements and pressure gradient effects, we are able to predict the swimming speed of the organisms in confined channels. Finally we study how Paramecium can swim and feed efficiently by stirring the fluid around its body. We experimentally employ "-Particle Image Velocimetry to characterize flows around the freely swimming Parameicum and numerically use Boundary Element Method to quantify the effect of body shapes on the swimming and feeding process. Results show that the body shape of Paramecium (slender anterior and bulky posterior) is hydrodynamically optimized to swim as well as feed efficiently. The dissertation makes significant advances in both experimentally characterizing and the- oretically understanding the flow field and locomotion patterns of ciliates near solid bound- aries.
  • Thumbnail Image
    Paramecium swimming in capillary tube
    Jana, Saikat; Um, S. H.; Jung, S. (American Institute of Physics, 2012-04-01)
    Swimming organisms in their natural habitat need to navigate through a wide range of geometries and chemical environments. Interaction with boundaries in such situations is ubiquitous and can significantly modify the swimming characteristics of the organism when compared to ideal laboratory conditions. We study the different patterns of ciliary locomotion in glass capillaries of varying diameter and characterize the effect of the solid boundaries on the velocities of the organism. Experimental observations show that Paramecium executes helical trajectories that slowly transition to straight lines as the diameter of the capillary tubes decreases. We predict the swimming velocity in capillaries by modeling the system as a confined cylinder propagating longitudinal metachronal waves that create a finite pressure gradient. Comparing with experiments, we find that such pressure gradient considerations are necessary for modeling finite sized ciliary organisms in restrictive geometries. (C) 2012 American Institute of Physics.
  • Thumbnail Image
    Somersault of Paramecium in extremely confined environments
    Jana, Saikat; Eddins, Aja; Spoon, Corrie E.; Jung, Sunghwan (Springer Nature, 2015-08-19)
    We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young's modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces.