Actuation, Sensing And Control For Micro Bio Robots

The continuing trend in miniaturization of technology, advancements in micro and nanofabrication and improvements in high-resolution imaging has enabled micro- and meso-scale robots that have many applications. They can be used for micro-assembly, directed drug delivery, microsurgery and high-resolution measurement. In order to create microrobots, microscopic sensors, actuators and controllers are needed. Unique challenges arise when building microscale robots. For inspiration, we look toward highly capable biological organisms, which excel at these length scales. In this dissertation we develop technologies that combine biological components and synthetic components to create actuation, sensing and assembly onboard microrobots. For actuation, we study the dynamics of synthetic micro structures that have been integrated with single-cell biological organisms to provide un-tethered onboard propulsion to the microrobot. For sensing, we integrate synthetically engineered sensor cells to enable a system capable of detecting a change in the local environment, then storing and reporting the information. Furthermore, we develop a bottom-up fabrication method using a macroscopic magnetic robot to direct the assembly of inorganic engineered micro structures. We showcase the capability of this assembly method by demonstrating highly-specified, predictable assembly of microscale building blocks in a semi-autonomous experiment. These magnetic robots can be used to program the assembly of passive building blocks, with the building blocks themselves having the potential to be arbitrarily complex. We extend the magnetic robot actuation work to consider control algorithms for multiple robots by exploiting spatial gradients of magnetic fields. This thesis makes contributions toward actuation, sensing and control of autonomous micro systems and provides technologies that will lead to the development of swarms of microrobots with a suite of manipulation and sensing capabilities working together to sense and modify the environment

Platinum-paper micromotors: An urchin-like nanohybrid catalyst for green monopropellant bubble-thrusters

Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two-dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50-63% over conventional materials and 13-19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust (\u3e0.5 N) from reagent grade H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact

Light controlled motility of Escherichia coli. Characterization and applications

Characterization of wild type E. coli motility in response to light stimuli. Gene editing of bacteria to implement specifc functions (e.g. photokinesis). The engineered strain has been used to demonstrate that density modulation of photokinetic bacteria can be obtained by projecting spatially structured light on the sample. Additionally these bacteria have been also used as propelling units in microfabricated structures

How dissipation constrains fluctuations in nonequilibrium liquids: Diffusion, structure and biased interactions

The dynamics and structure of nonequilibrium liquids, driven by non-conservative forces which can be either external or internal, generically hold the signature of the net dissipation of energy in the thermostat. Yet, disentangling precisely how dissipation changes collective effects remains challenging in many-body systems due to the complex interplay between driving and particle interactions. First, we combine explicit coarse-graining and stochastic calculus to obtain simple relations between diffusion, density correlations and dissipation in nonequilibrium liquids. Based on these results, we consider large-deviation biased ensembles where trajectories mimic the effect of an external drive. The choice of the biasing function is informed by the connection between dissipation and structure derived in the first part. Using analytical and computational techniques, we show that biasing trajectories effectively renormalizes interactions in a controlled manner, thus providing intuition on how driving forces can lead to spatial organization and collective dynamics. Altogether, our results show how tuning dissipation provides a route to alter the structure and dynamics of liquids and soft materials.Comment: 21 pages, 7 figure

High Aspect Ratio Carbon Nanotube Membranes Decorated with Pt Nanoparticle Urchins for Micro Underwater Vehicle Propulsion via H2O2 Decomposition

The utility of unmanned micro underwater vehicles (MUVs) is paramount for exploring confined spaces, but their spatial agility is often impaired when maneuvers require burst-propulsion. Herein we develop high-aspect ratio (150:1), multiwalled carbon nanotube microarray membranes (CNT-MMs) for propulsive, MUV thrust generation by the decomposition of hydrogen peroxide (H2O2). The CNT-MMs are grown via chemical vapor deposition with diamond shaped pores (nominal diagonal dimensions of 4.5 × 9.0 μm) and subsequently decorated with urchin-like, platinum (Pt) nanoparticles via a facile, electroless, chemical deposition process. The Pt-CNT-MMs display robust, high catalytic ability with an effective activation energy of 26.96 kJ mol–1 capable of producing a thrust of 0.209 ± 0.049 N from 50% [w/w] H2O2 decomposition within a compact reaction chamber of eight Pt-CNT-MMs in series

Engineering the “Pluripotency” of Zr-based Bulk Metallic Glasses as Biomedical Materials

Bulk metallic glasses (BMGs) are a family of novel alloys with amorphous microstructures. The combination of their excellent mechanical properties, good chemical stability, high thermal formability, and general biocompatibility has brought up new opportunities for biomaterials. Research in this dissertation was focused on exploring multiple biomedical functionalities of Zr-based BMGs over a wide spectrum, combining materials and biological characterizations, through experimental and computational approaches. Four distinct yet interconnected tasks were endeavored, involving inflammation, hard-tissue implant, soft-tissue prosthesis, and pathogenic infection. The inflammation that can be potentially triggered by Zr-based BMGs was investigated using macrophages. Lower level or comparable macrophage activations on were observed on Zr-based BMGs in comparison to commercial bio-alloys. The environmental stimuli can induce profound effects on macrophage activation in addition to substrate stimulation. Meanwhile, microstructure of the substrate was found to affect macrophage responses. Ion implantation was employed to engineer the surface of a Zr-Al-Ni-Cu-Y BMG to enhance bone integration. Low energy Ca-ion implantations were adopted, which altered surface materials properties and introduced enhanced bone-forming cell adhesion. With higher fluence Ar-ion implantations, nano-sized Ar-bubbles were doped in the surface region of the Zr-based BMG, causing surface softening, which can be subsequently sensed by bone-forming cells. Cells exhibited less established adhesion and actin filament formation, whereas, higher rate of proliferation on surfaces with lower stiffness. The potential of a Zr-Al-Fe-Cu BMG as a stent material was examined for the first time. The advantageous materials properties of the Zr-based BMG were revealed, including high strength, low elastic modulus, high elastic limit, and high biostability. Cell culture assays illustrated stronger adhesion and faster coverage of endothelial cells and slower growth of smooth muscle cells on the Zr-based BMG than on 316L stainless steel, which suggested promoted re-endothelialization and potentially lower risk of restenosis on the Zr-based BMG. The capability to fight implant infections stacked additional biomedical benefits to Zr-based BMGs. The potency of Zr-Al-Ni-Cu(-Y) and Zr-Al-Co-Ag BMGs to inhibit bacterial growth were demonstrated against Gram positive Staphylococcus aureus. The biocidal effects of these Zr-based BMGs were related to the heavy-metal-ion release and microstructure

Particle, Polymer & Phase Dynamics In Living Fluids

Flocks of birds, schools of fish, and jams in traffic surprisingly mirror the collective motion observed in the microscopic wet worlds of living microbes, such as bacteria. While these small organisms were discovered centuries ago, scientists have only recently examined the dynamics and mechanics of suspensions that contain these swimming particles. I conduct experiments with the model organism and active colloid, the bacterium Escherichia coli, and use polymers, particles, and phase-separated mixtures to probe the non-equilibrium dynamics of bacterial suspensions. I begin by examining the hydrodynamic interactions between swimming E. coli and particles. For dilute suspensions of bacteria in Newtonian fluids, I find that larger particles can diffuse faster than smaller particles - a feature absent in passive fluids, which may be important in particle transport in bio- and geo-physical settings populated by microbes. Next, I investigate E. coli dynamics in non-Newtonian polymeric solutions. I find that cells tumble less and move faster in polymeric solutions, enhancing cell translational diffusion. I show that tumbling suppression is due to fluid viscosity while the enhancement in swimming speed is due to fluid elasticity. Visualization of single fluorescently-labeled DNA polymers reveals that the flow generated by individual E. coli is sufficiently strong that polymers can stretch and induce elastic stresses in the fluid. These, in turn, can act on the cell in such a way to enhance its transport. Lastly, I probe the interplay between kinetics, mechanics, and thermodynamic of active fluids by examining the evolution of an active-passive phase interphase. I create this interface by exposing regions of a dense bacterial swarm to UV light, which locally immobilizes the bacteria. Vortices etch the interface, setting interface curvature and speed. The local interface curvature correlates with the interface velocity, suggesting an active analog of the Gibbs-Thomson boundary condition. My results have implications for the burgeoning field of active soft matter, including insight into their bulk rheology, how material properties are defined and measured, and their thermodynamics and kinetics

A Tracking Review on Non Arc Melting Processes for Improved Surface Properties in Metallic Materials

Most metallic materials lack the adequate surface characteristics to satisfactorily perform intended service functions. In such instance, the surface properties are modified by altering the chemistry, structure and/topology of the top surface of the surface via modification techniques. There exists wide options of techniques for modifying the surface properties and these are well documented in the literature. However, these techniques have different scientific underpinnings controlling them such that it is difficult to use a single mechanism to characterize the techniques. Arising from this, it is imperative that a holistic understanding of the various processes is provided. Therefore, in this paper, research status on the wide range of non-melting technique for surface modification is presented. The presentation discusses the investigation conducted on the various non-surface melting techniques and provides a comparison across the techniques. Recent developments in these techniques are equally presented. Existing challenges and emerging trends in the field are also highlighted.  . Keywords: coating composition, coating techniques, metallic materials, substrate, surface properties DOI: 10.7176/CMR/13-2-01 Publication date:May 31st 202

Geometric and Topological Aspects of Soft & Active Matter

Topological and geometric ideas are now a mainstay of condensed matter physics, underlying much of our understanding of conventional materials in terms of defects and geometric frustration in ordered media, and protected edge states in topological insulators. In this thesis, I will argue that such an approach successfully identifies the relevant physics in metamaterials and living matter as well, even when traditional techniques fail. I begin with the problem of kirigami mechanics, i.e., designing a pattern of holes in a thin elastic sheet to engineer a specific mechanical response. Using an electrostatic analogy, I show that holes act as sources of geometric incompatibility, a feature that can fruitfully guide design principles for kirigami metamaterials. Next I consider nonequilibrium active matter composed of self-driven interacting units that exhibit large scale collective and emergent behaviour, as commonly seen in living systems. By focusing on active liquid crystals in two dimensions, with both polar and nematic orientational order, I show how broken time-reversal symmetry due to the active drive allows polar flocks on a curved surface to support topologically protected sound modes. In an active nematic, activity instead causes topological disclinations to become spontaneously motile, driving defect unbinding to organize novel phases of defect order and chaos. In all three cases, geometric and topological ideas enable the relevant degrees of freedom to be identified, allowing complex phenomena to be treated in a tractable fashion, with novel and surprising consequences along the way