Edward B. Steager

Control of microfabricated structures powered by flagellated bacteria using phototaxis

Flagellated bacteria have been employed as microactuators in low Reynolds number fluidic environments. SU-8 microstructures have been fabricated and released on the surface of swarming Serratia marcescens, and the flagella propel the structures along the swarm surface. Phototactic control of these structures is demonstrated by exposing the localized regions of the swarm to ultraviolet light. The authors additionally discuss the control of microstructures in an open channel powered by bacteria which have been docked through a blotting technique. A tracking algorithm has been developed to analyze swarming patterns of the bacteria as well as the kinematics of the microstructures.

Single Cell Manipulation using Ferromagnetic Composite Microtransporters

For biomedical applications, such as single cell manipulation, it is important to fabricate microstructures that can be powered and controlled wirelessly in fluidic environments. In this letter, we describe the construction and operation of truly micron-sized, biocompatible ferromagnetic microtransporters driven by external magnetic fields. Microtransporters were fabricated using a simple, single step fabrication method and can be produced in large numbers. We demonstrate that they can be navigated to manipulate single cells with micron-size precision without disturbing the local environment.

Electrokinetic and optical control of bacterial microrobots

One of the great challenges in microscale science and engineering is the independent manipulation of cells and man-made objects on the micron scale. For such work, motile microorganisms are integrated with engineered systems to construct microbiorobots (MBRs). MBRs are negative photosensitive epoxy (SU-8) microfabricated structures with typical feature sizes ranging from 1 to 100 µm coated with a monolayer of swarmer cells of the bacterium Serratia marcescens. The adherent cells naturally coordinate to propel the microstructures in fluidic environments. In this study, ultraviolet light is used to control rotational motion and direct current electric fields are used to control the two-dimensional movement of MBRs. They are steered in a fully automated fashion using computer-controlled visual servoing, used to transport and manipulate micron-sized objects, and employed as cell-based biosensors. This work is a step toward in vitro mechanical or chemical manipulation of cells as well as controlled assembly of microcomponents.

Automated biomanipulation of single cells using magnetic microrobots

Transport of individual cells or chemical payloads on a subcellular scale is an enabling tool for the study of cellular communication, cell migration, and other localized phenomena. We present a magnetically actuated robotic system capable of fully automated manipulation of cells and microbeads. Our strategy uses autofluorescent robotic transporters and fluorescently labeled microbeads to aid tracking and control in optically obstructed environments. We demonstrate automated delivery of microbeads infused with chemicals to specified positions on neurons. This system is compatible with standard upright and inverted light microscopes and is capable of applying forces less than 1 pN for precision positioning tasks.

Modeling, control and experimental characterization of microbiorobots

In this paper, we describe how motile microorganisms can be integrated with engineered microstructures to develop a micro-bio-robotic system. SU-8 microstructures blotted with swarmer cells of Serratia Marcescens in a monolayer are propelled by the bacteria in the absence of any environmental stimulus. We call such microstructures with bacteria MicroBioRobots (MBRs) and the uncontrolled motion in the absence of stimuli self actuation. Our paper has two primary contributions. First, we demonstrate the control of MBRs using self actuation and DC electric fields, and develop an experimentally validated mathematical model for the MBRs. This model allows us to use self actuation and electrokinetic actuation to steer the MBR to any position and orientation in a planar micro channel. Second, we combine our experimental setup and a feedback control algorithm to steer robots with micrometer accuracy in two spatial dimensions. We describe the fabrication process for MBRs and show experimental results demonstrating actuation and control.

Wireless manipulation of single cells using magnetic microtransporters

For such biomedical applications as single cell manipulation and targeted delivery of chemicals, it is important to fabricate microstructures that can be powered and controlled without a tether in fluidic environments. In this work, we describe the construction and operation of micronsized, biocompatible ferromagnetic microtransporters driven by external magnetic fields capable of exerting forces at the pico Newton scale. We develop microtransporters using a simple, single step micro fabrication technique that allows us to produce large numbers in the same step. We also fabricate microgels to deliver drugs. We demonstrate that the microtransporters can be navigated to separate individual targeted cells with micron-scale precision, and deliver microgels without disturbing the cells in the neighborhood and the local microenvironment.

Dynamics of pattern formation in bacterial swarms

To gain a more thorough understanding of the dynamics of swarming bacteria, a nonlabeled cell tracking algorithm was used to study the velocity field of flagellated bacteria, Serratia marcescens, swarming on a soft agar plate. The average velocities for local regions regularly arranged over the entire flow field were investigated. The velocity field of the bacteria typically featured the combination of curvilinear translation and vortex modes. They repeated these patterns for short periods of time, forming several groups and dissipating. To further investigate the flow patterns generated by the collective motion of the swarming bacteria, the velocity field on the swarm was spatially correlated. The highest velocities and correlation lengths have been found to occur in the region from 0.5to1mm from the swarm edge, followed by a steady decline as distance from the edge increases, and a sudden decrease in motion typically occurs between 2 and 4mm from the swarm edge.

Biosensing and actuation for microbiorobots

In this paper, we describe how signaling networks and actuation in bacterial cells and biomolecular networks of bacteria can be used to develop an integrated micro-bio-robotic system. SU8 microstructures blotted with swarmer cells of Serratia Marcescens in a monolayer are propelled by the bacteria in the absence of any environmental stimulus. We call such microstructures with bacteria Micro Bio Robots (MBRs) and the uncontrolled motion in the absence of stimuli self actuation. Our paper has two primary contributions. First, we demonstrate the control of MBRs using self-actuation, DC electric fields and ultra-violet radiation, and develop experimentally validated mathematical model for the MBRs. This model allows us to use self-actuation and electrokinetic actuation to steer the MBR to any position and orientation in a planar micro channel. Second, we describe the development of biosensors for the MBRs. This is done by attaching genetically engineered Escherichia coli cells that are capable of sensing nonmetabolizable lactose analog methyl-β-D-thiogalactoside (TMG). We describe the fabrication process for MBRs and show experimental results demonstrating sensing, actuation and control.

Effect of surface interactions and geometry on the motion of micro bio robots

Micro Bio Robots (MBRs) are synthetic microstructures with a monolayer of flagellated bacteria adhered to the surface. The flagella of the bacteria propel the microstructure causing it to rotate and translate in a fluidic environment on a planar surface in the absence of external forces. This paper investigates the force contributions of bacteria adhered to the edge versus the center of the micro-structure by selectively altering their behavior using near-UV light. In particular, we investigate the forces that cause predominant clockwise MBR rotation when viewed from above. Additionally, asymmetric shapes, particularly gears, are used to compare the effect of the adherent bacteria with that of collisions among free-swimming bacteria and the microstructure. We find that bacteria adhered near the edge of the MBR interact with the glass substrate under the MBR, accounting for statistically biased clockwise rotation of MBRs.

Harnessing bacterial power in microscale actuation

This paper presents a systematic analysis of the motion of microscale structures actuated by flagellated bacteria. We perform the study both experimentally and theoretically. We use a blotting procedure to attach flagellated bacteria to a buoyancy-neutral plate called a microbarge. The motion of the plate depends on the distribution of the cells on the plate and the stimuli from the environment. We construct a stochastic mathematical model for the system, based on the assumption that the behavior of each bacterium is random and independent of that of its neighbors. The main finding of the paper is that the motion of the barge plus bacteria system is a function of a very small set of parameters. This reduced-dimensional model can be easily estimated using experimental data. We show that the simulation results obtained from the model show an excellent match with the experimentally-observed motion of the barge.