“…Here, we tackle this challenge by using OTV (Wei et al 2019;Dehnavi et al 2020). Previously, optical tweezers have been employed to measure velocity of steady flows (Almendarez-Rangel et al 2018). In this study, we leverage the high spatial-temporal resolution of the optical tweezers-based measurement to resolve both the steady and the unsteady component of the ciliary flow.…”
“…Here, we tackle this challenge by using OTV (Wei et al 2019;Dehnavi et al 2020). Previously, optical tweezers have been employed to measure velocity of steady flows (Almendarez-Rangel et al 2018). In this study, we leverage the high spatial-temporal resolution of the optical tweezers-based measurement to resolve both the steady and the unsteady component of the ciliary flow.…”
“…Here, we use optical tweezers-based velocimetry (OTV) [24,25] to measure unsteady flows around a cilium. We find the flow to differ fundamentally from the flow predicted in the zero Re regime.…”
mentioning
confidence: 99%
“…In our OTV method, we directly measure the hydrodynamic force exerted on a microbead to determine the flow velocity [24,25]. The optical tweezers setup is similar to Ref.…”
Stokes equations are commonly used to model the hydrodynamic flow around cilia on the micron scale. The validity of the zero Reynolds number approximation is investigated experimentally with a flow velocimetry approach based on optical tweezers, which allows the measurement of periodic flows with high spatial and temporal resolution. We find that beating cilia generate a flow, which fundamentally differs from the stokeslet field predicted by Stokes equations. In particular, the flow velocity spatially decays at a faster rate and is gradually phase delayed at increasing distances from the cilia. This indicates that the quasisteady approximation and use of Stokes equations for unsteady ciliary flow are not always justified and the finite timescale for vorticity diffusion cannot be neglected. Our results have significant implications in studies of synchronization and collective dynamics of microswimmers.
“…Because the particle Reynolds number is low and inertia, added mass, and Basset forces are negligible ( 45 ), the Boussinesq-Basset-Oseen equation can be reduced to a first-order equation in which the trapping force and hydrodynamic drag are balanced, or , where . Similar methods have been used in previous studies to measure flows in microfluidic devices ( 46 , 47 , 48 , 49 ). Figure 4 Optical tweezers-based velocimetry (OTV).…”
The flagella of
Chlamydomonas reinhardtii
possess fibrous ultrastructures of a nanometer-scale thickness known as mastigonemes. These structures have been widely hypothesized to enhance flagellar thrust; however, detailed hydrodynamic analysis supporting this claim is lacking. In this study, we present a comprehensive investigation into the hydrodynamic effects of mastigonemes using a genetically modified mutant lacking the fibrous structures. Through high-speed observations of freely swimming cells, we found the average and maximum swimming speeds to be unaffected by the presence of mastigonemes. In addition to swimming speeds, no significant difference was found for flagellar gait kinematics. After our observations of swimming kinematics, we present direct measurements of the hydrodynamic forces generated by flagella with and without mastigonemes. These measurements were conducted using optical tweezers, which enabled high temporal and spatial resolution of hydrodynamic forces. Through our measurements, we found no significant difference in propulsive flows due to the presence of mastigonemes. Direct comparison between measurements and fluid mechanical modeling revealed that swimming hydrodynamics were accurately captured without including mastigonemes on the modeled swimmer’s flagella. Therefore, mastigonemes do not appear to increase the flagella’s effective area while swimming, as previously thought. Our results refute the longstanding claim that mastigonemes enhance flagellar thrust in
C. reinhardtii
, and so, their function still remains enigmatic.
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