Locomotion ofmicroorganisms through the rotation of flagella (some slender helicalfilaments) in viscous fluids is ubiquitous [1]. However, experimentalmanipulation of micron-sized bacterial flagella is difficult, and oftenimpossible. Currently, other researchers already devised several macroscopicmodels that only focused on a single function, like flagella bundle observationor propulsion force measurement [1-3].

Fig. 1 Micron-sized peritrichous Escherichia coli, reproduced from Turner et al. [4]

Based on customer requirements, our group proposes a macroscopicexperimental facility that integrates propulsion force measurement and flagella interaction observation.

Fig. 2 CAD figure of the overallsystem

Fig. 3 Concept diagram

To generate the helix motion at different spatial configurations, amotor platform based on slider-slideway is designed, on which the helices arefixed and their motion is actuated through motors.

For propulsion force measurement, a compression spring platform isdesigned to balance the weight of the big tank so that a digital balance withhigh precision can be applied here.

To collect image data, a two-camera-synchronization system ischosen to record the video data from different angles.

Macroscopic helix models with bionic hooks are designed to mimicthe actual geometry of flagella.

Fig. 4 The whole set-up of the system

Validation Process:

Force measurement is calibrated by adjusting the vertical platformtill touching tank stand board bottom.

Video data are acquired by one PC.

Validation Results:

Fig. 6  Image recorded by twocameras

Via two-camera-synchronization system, the bundling phenomenon is observed.

Fig. 7 Bundling phenomenon

Also, most specifications can be met.

√Reynolds number < 0.1

√Camera’s frame rate >= 40 fps

√Sensitivity of digital balance = 1 mg

√Cost <= 8000 RMB

• Motor’s torque output >= 0.5 N·m            

√ means having been verifiedand · means to be determined.

The selections of compression springs and motors are based oncalculation of the design requirements.

Fig. 5 Working principleillustration of the force measurement system

Parameters of helices are determined by several dimensionless numbers:

Re=ρωR d /η, and M=(64ηωL^4)/(πEd^4 ), which require Re < 0.1, M ≈ 150 to mimic micron-sized hydrodynamic condition.

Our project allows researchers to deeply understand flagella bymacroscopic experiments. In the future, extension functions can be added tosolve more problems in micron-sized world.

Sponsor: Zijie Qu from UM-SJTU Joint Institute

Instructor: Jigang Wu from UM-SJTU Joint Institute

[1] Lauga E. 2016. Bacterial Hydrodynamics. Annu. Rev. Fluid Mech.

[2] Kim MJ, Bird JC, Parys AJV, Breuer KS, Powers TR. 2003. Amacroscopic scale model of bacterial flagellar bundling. PNAS.

[3] Liu B, Powers TR, Breuer KS. 2011. Force-free swimming of amodel helical flagellum in viscoelastic fluids. PNAS.

[4] Turner L, Ryu WS, Berg HC. 2000. Real-time imaging offluorescent flagellar filaments. J. Bacteriol.