Hydrodynamics of a self-actuated bacterial carpet using microscale particle image velocimetry

Abstract

Microorganisms can effectively generate propulsive force at the microscale where viscous forces overwhelmingly dominate inertia forces; bacteria achieve this task through flagellar motion. When swarming bacteria, cultured on agar plates, are blotted onto the surface of a microfabricated structure, a monolayer of bacteria forms what is termed a "bacterial carpet," which generates strong flows due to the combined motion of their freely rotating flagella. Furthermore, when the bacterial carpet coated microstructure is released into a low Reynolds number fluidic environment, the propulsive force of the bacterial carpet is able to give the microstructure motility. In our previous investigations, we demonstrated motion control of these bacteria powered microbiorobots (MBRs). Without any external stimuli, MBRs display natural rotational and translational movements on their own; this MBR self-actuation is due to the coordination of flagella. Here, we investigate the flow fields generated by bacterial carpets, and compare this flow to the flow fields observed in the bulk fluid at a series of locations above the bacterial carpet. Using microscale particle image velocimetry, we characterize the flow fields generated from the bacterial carpets of MBRs in an effort to understand their propulsive flow, as well as the resulting pattern of flagella driven self-actuated motion. Comparing the velocities between the bacterial carpets on fixed and untethered MBRs, it was found that flow velocities near the surface of the microstructure were strongest, and at distances far above, the surface flow velocities were much smaller.

A dynamic preferred direction model for the self-organization dynamics of bacterial microfluidic pumping

“…III C, at y = ±b/2 we fix W = W 0êx , where W 0 is the actual bulk equilibrium value of |W| in the absence of noise (Eqs. (5) and (8) are strong-and weak-coupling limits of the magnitude used here). At x = ±a/2, zero gradient boundary condition ∂W/∂x = 0 is applied.…”

“…Since the pioneering work by Kim and Breuer on self-organizing bacteria carpets leading to microfluidic pumping [1][2][3][4][5], the phenomena of bacterial self-organization resulting in spontaneous fluid flow are meanwhile readily reproduced and are already exploited on a level approaching applications [6][7][8][9][10][11][12]. In a qualitative picture, the mechanism responsible for all these spontaneously driven flows is considered to be collective coordination between individual bacteria caused by fluid flow that is generated by their flagella.…”

Autonomous dynamic obstacle avoidance for bacteria-powered microrobots (BPMs) with modified vector field histogram

“…To generate propulsive force at low Reynolds number, the BPMs utilize hydrodynamics of flagella from the bacterial carpet attached to the bottom of the SU-8 microstructure. The hydrodynamics is the result of individual bacteria flagellar waving [ 29 ]. The flagella on the carpet undergo corkscrew motions which are nonreciprocal and the collective motion of the flagella helps the BPM to overcome friction on the bottom surface and the viscosity present in a low Reynolds fluid.…”

µ-PIV Measurements of Flows Generated by Photolithography-Fabricated Achiral Microswimmers

“…As shown in Figure 2, the coil system was powered by three power supplies (Kepco BOP20-5M) and controlled by a National Instrument (NI) Data Acquisition (DAQ) device (PCI-6259) and a LabVIEW interface. Flow velocity measurements were obtained using previously reported methods [33,38]. The PIV experiments were conducted in water at room temperature (~1 cP).…”

“…For the past few years, µ-PIV had been used to study the flows of a number of different microswimmers. For example, µ-PIV was used to further the understanding of the swimming behavior of microorganisms [30][31][32], as well as a microorganism-based microswimmer [33], while stereoscopic µ-PIV measurements were used to confirm the asymmetric dynamic motion of artificial cilia that can generate 3D asymmetric dipole vortices [34]. For helical microswimmers, [35,36] studied the thrust force and efficiency of helical microswimmers using µ-PIV with both micro-and macroscale models.…”