Bacteria-Propelled Microswimmers

Loading Physical Intelligence Department

S. marcescens bacteria attached to PS bead (Kim et al., Biomed Microdevices, 2012).


Project Members:

  • To develop and control dense networks of bacteria-driven swimming microrobots


  • To have a detailed understanding of the mechanism of flagella team-work in bacterial propulsion


  • To investigate the use of different particle patterns or different bodies for building bacteria-bots


  • To gain an efficient and directed propulsion for the swimming microrobots


  • To use bacteria-bots for targeted drug delivery by means of different strategies (bacterial sensory drive or external force)



Jiang Zhuang

Babak Mostaghaci

Zeinab Hosseini-Doust

Past Members:

Bahareh Behkam

Rika Carlsen

Selected Research Results and Papers

Magnetic Steering Control of Multi-Cellular Bio-Hybrid Microswimmers

Bio-hybrid devices, which integrate biological cells with synthetic components, have opened a new path in miniaturized systems with the potential to provide actuation and control for systems down to a few microns in size. Here, we address the challenge of remotely controlling bio-hybrid microswimmers propelled by multiple bacterial cells. These devices have been proposed as a viable method for targeted drug delivery but have also been shown to exhibit stochastic motion. We demonstrate a method of remote magnetic control that significantly reduces the stochasticity of the motion, enabling steering control. The demonstrated microswimmers consist of multipleSerratia marcescens (S. marcescens) bacteria attached to a 6 μm-diameter superparamagnetic bead. We characterize their motion and define the parameters governing their controllability. We show that the microswimmers can be controlled along two-dimensional (2-D) trajectories using weak magnetic fields (≤10 mT) and can achieve 2-D swimming speeds up to 7.3 μm s−1. This magnetic steering approach can be integrated with sensory-based steering in future work, enabling new control strategies for bio-hybrid microsystems.

R. Carlsen, M. Edwards, J. Zhuang and M. Sitti, “Magnetic Steering Control of Multi-Cellular Bio-Hybrid Microswimmers”, Lab on Chip 14, 3850-3859, 2014.

Future direction of integrating external and sensory-based control of bacteria-propelled microswimmers.

Near and Far-Wall Effects on the Three Dimensional Motion of Bacteria-Driven Microbeads

Bio-hybrid microrobots have been heavily studied due to their potential applications as minimally invasive medical microdevices. Though most researchers have focused on two-dimensional and near-wall motion, this letter uses a defocused optical tracking method to quantify the three-dimensional motion of 5 μm diameter polystyrene beads driven by attached Serratia marcescensbacteria. Away from walls, the beads trace out helical trajectories, demonstrating kinematicsproduced by near-constant forces and torques. Near-wall motion is observed to be more stochastic. The motion of beads driven by single bacteria is analyzed in detail, providing an understanding of the forces and torques on the beads.

M. Edwards, R. Carlsen, and M. Sitti, "Near and Far-Wall Effects on the Three Dimensional Motion of Bacteria-Driven Microbeads", Applied Physics Letters 102, 143701, 2013.

Phase contrast microscopy images of 5 μm polystyrene beads at different z displacements

Chemotactic Steering of Bacteria Propelled Microbeads

Flagellated bacteria have been embraced by the microrobotics community as a highly efficient microscale actuation method, capable of converting chemical energy into mechanical actuation for microsystems that require a small payload and high rate of actuation. Along with being highly motile, Serratia marcescens (S. marcescens), our bacterium species of interest, is a highly agile biomotor capable of being steered via chemotaxis. In this paper, we attached S. marcescens bacteria to polystyrene microbeads towards creating biohybrids that can propel themselves towards an attractive chemical source. Using a three-channel microfluidic device, linear chemical gradients are generated to compare the behavior of bacteria-propelled beads in the presence and absence of a chemoattractant, L-aspartate. We tested and compared the behavior of three different bacteria-attached bead sizes (5, 10 and 20 μm diameter) using a visual particle-tracking algorithm, and noted their behavioral differences. The results indicate that in the presence of a chemoattractant, the S. marcescens-attached polystyrene beads exhibit a clear indication of directionality and steering control through the coordination of the bacteria present on each bead. This directionality is observed in all bead size cases, suggesting potential for targeted payload delivery using such a biohybrid microrobotic approach.

D. Kim, A. Liu, E. Diller, and M. Sitti, "Chemotactic Steering of Bacteria Propelled Microbeads," Biomedical Microdevices 14, 1009-17, Dec 2012.

20 μm diameter beads suspended in motility medium. Attached bacteria can be seen roughly as black spots on the bead surfaces

PDMS-Agarose microfluidic model to investigate the chemotactic steering of the bacteria.

Modeling of Stochastic Motion of Bacteria Propelled Spherical Microbeads

This work proposes a stochastic dynamic model of bacteria propelled spherical microbeads as potential swimming microrobotic bodies. Small numbers of S. marcescensbacteria are attached with their bodies to surfaces of spherical microbeads. Average-behavior stochastic models that are normally adopted when studying such biological systems are generally not effective for cases in which a small number of agents are interacting in a complex manner, hence a stochastic model is proposed to simulate the behavior of 8-41 bacteria assembled on a curved surface. Flexibility of the flagellar hook is studied via comparing simulated and experimental results for scenarios of increasing bead size and the number of attached bacteria on a bead. Although requiring more experimental data to yield an exact, certain flagellar hook stiffness value, the examined results favor a stiffer flagella. The stochastic model is intended to be used as a design and simulation tool for future potential targeted drug delivery and disease diagnosis applications of bacteria propelled microrobots.

V. Arabagi, B. Behkam, E. Cheung, and M. Sitti, "Modeling of Stochastic Motion of Bacteria Propelled Spherical Microbeads," Journal of Applied Physics 109, 114702, 2011.

Trapping and transportation of a living motile bacterium

Bacterial Flagella-Based Propulsion and On/Off Motion Control of Microscale Objects

Miniaturization of the power source and on-board actuation is the main bottleneck for the development of microscale mobile robots. As a possible solution, this letter proposes the use of flagellar motors inside the intact cell of Serratia marcescensbacteria for controlled propulsion of swimming robotic bodies. The feasibility of the proposed idea is demonstrated by propelling 10μm polystyrene beads at an average speed of 15±6μm∕s  by several bacteria randomly attached on their surface. On/off motion control of the bead is achieved by introducing copper ions to stop the bacteria flagellar motors and ethylenediaminetetraacetic acid to resume their motion.

B. Behkam and M. Sitti, "Bacterial Flagella-Based Propulsion and On/Off Motion Control of Microscale Objects," Applied Physics Letters, vol. 90, pp. 23902-23904, 14 Jan. 2007. Also appeared on the Virtual Journal of Nanoscale Science & Technology, vol. 15, no. 2, January 15, 2007.

Phase-contrast optical microscope images of a mobile 10μm PS bead with several S. marcescens bacteria attached to it at (a) t=0 and (b) t=6s.

Selected Videos

Bacteria Propelled Microbeads (2012)

Polystyrene (PS) microbead propelled by attached bacteria  (2007)

Swimming millirobot  (2005)

Chemotactic Steering Response of Bacteria Propelled Microbeads (2012)

10 micron PS bead propelled by the attached S. marcescens bacteria

Swimming millirobot inside an oil tank inspired by bacteria travelling through viscous fluid

List of Publications



Bio‐Hybrid Cell‐Based Actuators for Microsystems

RW Carlsen, M Sitti

Small 10 (19), 3831–3851



Magnetic steering control of multi-cellular bio-hybrid microswimmers

RW Carlsen, MR Edwards, J Zhuang, C Pacoret, M Sitti

Lab on a Chip 14 (19), 3850-3859





Near and far-wall effects on the three-dimensional motion of bacteria-driven microbeads

MR Edwards, RW Carlsen, M Sitti

Applied Physics Letters 102 (14), 143701




Chemotactic steering of bacteria propelled microbeads

D Kim, A Liu, E Diller, M Sitti

Biomedical microdevices 14 (6), 1009-1017





Chemotactic behavior and dynamics of bacteria propelled microbeads

D Kim, A Liu, M Stitti

Intelligent Robots and Systems (IROS), 2011 IEEE/RSJ International ...



Micro-scale propulsion using multiple flexible artificial flagella

J Singleton, E Diller, T Andersen, S Regnier, M Sitti

Intelligent Robots and Systems (IROS), 2011 IEEE/RSJ International ...



Modeling of stochastic motion of bacteria propelled spherical microbeads

V Arabagi, B Behkam, E Cheung, M Sitti

Journal of Applied Physics 109 (11), 114702





Bacterial flagella assisted propulsion of patterned latex particles: Effect of particle size

B Behkam, M Sitti

Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on, 723-727





Towards hybrid swimming microrobots: bacteria assisted propulsion of polystyrene beads

B Behkam, M Sitti

Engineering in Medicine and Biology Society, 2006. EMBS'06. 28th Annual ...



Design methodology for biomimetic propulsion of miniature swimming robots

B Behkam, M Sitti

Trans.-ASME Journal of Dynamic Systems Measurement and Control 128 (1), 36





Modeling and testing of a biomimetic flagellar propulsion method for microscale biomedical swimming robots

B Behkam, M Sitti

Proceedings of Advanced Intelligent Mechatronics Conference, 37-42





E. coli inspired propulsion for swimming microrobots

B Behkam, M Sitti

ASME 2004 International Mechanical Engineering Congress and Exposition, 1037 ...





Biomimetic propulsion for a swimming surgical micro-robot

J Edd, S Payen, B Rubinsky, ML Stoller, M Sitti

Intelligent Robots and Systems, 2003.(IROS 2003). Proceedings. 2003 IEEE/RSJ ...