We present a path planning strategy for a magnetic millirobot where the nonlinearities in the external magnetic force field (MFF) are encoded in the graph used for planning. The strategy creates a library of candidate MFFs and characterizes their topologies by identifying the unstable manifolds in the workspace. The path planning problem is then posed as a graph search problem where the computed path consists of a sequence of unstable manifold segments and their associated MFFs. By tracking the robot's position and sequentially applying the MFFs, the robot navigates along each unstable manifold until it reaches the goal. We discuss the theoretical guarantees of the proposed strategy and experimentally validate the strategy.

In this work, we explore a unique approach to harvest energy from active matter in order to independently power and control many untethered, mobile microrobots. More specifically, we investigate microstructure transport caused by stochastic collisions between freely swimming cells and rigid microstructure boundaries in a dense bacterial bath. We characterize the motion of asymmetrically shaped microstructures, specifically gears and chevrons, and demonstrate control of these microrobots by altering the motility of swimming cells with high intensity blue light. We demonstrate both rotational and translational motion control using a custom system for tracking and real-time automated exposure of local bath regions using visual feedback. These experiments are supported by a mathematical model and simulations which describe the dynamics of a microstructure propelled by many stochastic cell structure collisions. This model allows us to predict microrobot trajectories and to develop improved strategies for microrobot design and control.

Independent control of several, untethered microrobots remains a significant challenge. Although progress has been made in controlling multiple robots at scales below 100 mm, motion is dependent on external energy sources for propulsion and is often not fully decoupled. Here, we develop a method to dynamically pattern light at a resolution of 1 μm2per pixel in a closed loop real-time system using a digital micromirror device (DMD) system. We test the system on microbiorobots - bacteria-coated microplates - and demonstrate that we can selectively stimulate pre-defined regions of bioactuators. We verify previously developed dynamic models as a step toward developing individually addressable, self-propelled microrobots.

Microscale robots offer an unprecedented opportunity to perform tasks at resolutions approaching 1 μm, but the great majority of research to this point focuses on actuation and control. Potential applications for microrobots can be considerably expanded by integrating sensing, signal processing and feedback into the system. In this work, we demonstrate that technologies from the field of synthetic biology may be directly integrated into microrobotic systems to create cell-based programmable mobile sensors, with signal processors and memory units. Specifically, we integrate genetically engineered, ultraviolet light-sensing bacteria with magnetic microrobots, creating the first controllable biological microrobot that is capable of exploring, recording and reporting on the state of the microscale environment. We demonstrate two proof-of-concept prototypes: (a) an integrated microrobot platform that is able to sense biochemical signals, and (b) a microrobot platform that is able to deploy biosensor payloads to monitor biochemical signals, both in a biological environment. These results have important implications for integrated micro-bio-robotic systems for applications in biological engineering and research.

For applications such as targeting therapeutic nanocarriers to specific tissues, as well as for the more general problem of assessing binding affinity between proteins, it is important to discover tools which may be used for both micromanipulation as well as force microscopy. In this work, we measure picoscale forces using microscale robots, using antibody-coated microbead probes as an interface. We develop a model for a detailed understanding of the relationship between robot velocity and applied force, and apply this to the measurement of binding forces between antibody-coated beads and protein-coated glass slides. We also verify binding between specific antibody/protein combinations relative to untargeted control combinations, and we measure the rate at which this binding occurs. This offers a truly novel technique for measuring binding forces between proteins.

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 for the 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.

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.

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.

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.