Bacterial actuation and manipulation are demonstrated where Magnetospirillum gryphiswaldense magnetotactic bacteria ͑MTB͒ are used to push 3 m beads at an average velocity of 7.5 m s −1 along preplanned paths by modifying the torque on a chain of magnetosomes in the bacterium with a directional magnetic field of at least 0.5 G generated from a small programmed electrical current. But measured average thrusts of 0.5 and 4 pN of the flagellar motor of a single Magnetospirillum gryphiswaldense and MC-1 MTB suggest that average velocities greater than 16 and 128 m s −1 , respectively could be achieved.The behaviors of bacteria in low Reynolds number hydrodynamics 1 suggest that they could be used to manipulate efficiently suspended micro-objects in fluids for potential applications in microsystems such as lab-on-a-chip and Micro-Total-Analysis Systems. Here, electro-osmosis 2 or dielectrophoresis 3 based on the principle of electrokinetics is used where frequencies and voltage amplitudes dependent on dielectric properties are required to induce a force. Our method referred here to as bacterial manipulation is independent of the dielectric properties and may prove to be suitable for many applications when low electrical power and compactness are required.The integration of bacteria as functional components has been previously done, 4,5 where Serratia marcescens flagellated bacteria were attached to polydimethylsiloxane or polystyrene to form a bacterial carpet for moving fluid. Until then, bacteria were operating without external control appropriate for manipulation of micro-objects. Typical bacteria swims according to the so-called run-and-tumble pattern that can be explained by chemotaxis 6 models while remaining unpredictable for micromanipulation. We show here that magnetotactic bacteria ͑MTB͒ are more appropriate to carry out computer-based controlled micromanipulation or microactuation of micro-objects.The exploitation of the motility of MTB has been done in the past such as in low field orientation magnetic separation 7 being a process, where motile, magnetic field susceptible MTB can be separated. Micromanipulation of MTB using microelectromagnets arrays has also been described. 8,9 In all these previous examples, MTB were the entities being manipulated instead of being used to manipulate other objects as described here.Each MTB ͑Ref. 10͒ possesses a chain of magnetosomes which are membrane-based nanoparticles of a magnetic iron. Because of this chain, the swimming direction of MTB although influenced by chemotaxis and aerotaxis is mainly based on magnetotaxis, 11-13 being more "compatible" with electronics and computer-based software platforms. Al-though several types of MTB exist and can be found all over the world, in this study, Magnetospirillum gryphiswaldense bacteria 14 were used. This MTB has a length of ϳ1-3 m with a swimming speed of ϳ40-80 m / s. Magnetotaxis as chemotaxis 15-17 also influences the motility of MTB in search of nutrient gradients. To modify the paths of the MTB, magnetic field lines ...

Navigating tethered instruments through the vasculatures to reach deeper physiological locations presently inaccessible would extend the applicability of many medical interventions, including but not limited to local diagnostics, imaging, and therapies. Navigation through narrower vessels requires minimizing the diameter of the instrument, resulting in a decrease of its stiffness until steerability becomes unpractical, while pushing the instrument at the insertion site to counteract the friction forces from the vessel walls caused by the bending of the instrument. To reach beyond the limit of using a pushing force alone, we report a method relying on a complementary directional pulling force at the tip created by gradients resulting from the magnetic fringe field emanating outside a clinical magnetic resonance imaging (MRI) scanner. The pulling force resulting from gradients exceeding 2 tesla per meter in a space that supports human-scale interventions allows the use of smaller magnets, such as the deformable spring as described here, at the tip of the instrument. Directional forces are achieved by robotically positioning the patient at predetermined successive locations inside the fringe field, a method that we refer to as fringe field navigation (FFN). We show through in vitro and in vivo experiments that x-ray–guided FFN could navigate microguidewires through complex vasculatures well beyond the limit of manual procedures and existing magnetic platforms. Our approach facilitated miniaturization of the instrument by replacing the torque from a relatively weak magnetic field with a configuration designed to exploit the superconducting magnet-based directional forces available in clinical MRI rooms.

We propose and experimentally demonstrate an on-chip all-optical differential-equation solver capable of solving second-order ordinary differential equations (ODEs) characterizing continuous-time linear time-invariant (LTI) systems. The photonic device is implemented by a self-coupled micro-resonator on a silicon-on-insulator (SOI) platform with mutual coupling between the cavity modes. Owing to the mutual mode coupling within the same resonant cavity, the resonance wavelengths induced by different cavity modes are self-aligned, thus avoiding precise wavelength alignment and unequal thermal wavelength drifts as in the case of cascaded resonators. By changing the mutual mode coupling strength, the proposed device can be used to solve second-order ODEs with tunable coefficients. System demonstration using the fabricated device is carried out for 10-Gb/s optical Gaussian and super-Gaussian input pulses. The experimental results are in good agreement with theoretical predictions of the solutions, which verify the feasibility of the fabricated device as a tunable second-order photonic ODE solver.

We propose and experimentally demonstrate an all-optical temporal differential-equation solver that can be used to solve ordinary differential equations (ODEs) characterizing general linear time-invariant (LTI) systems. The photonic device implemented by an add-drop microring resonator (MRR) with two tunable interferometric couplers is monolithically integrated on a silicon-on-insulator (SOI) wafer with a compact footprint of ~60 μm × 120 μm. By thermally tuning the phase shifts along the bus arms of the two interferometric couplers, the proposed device is capable of solving first-order ODEs with two variable coefficients. The operation principle is theoretically analyzed, and system testing of solving ODE with tunable coefficients is carried out for 10-Gb/s optical Gaussian-like pulses. The experimental results verify the effectiveness of the fabricated device as a tunable photonic ODE solver.

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We demonstrate a compact silicon polarization beam splitter (PBS) based on grating-assisted contradirectional couplers (GACCs). Over 30-dB extinction ratios and less than 1-dB insertion losses are achieved for both polarizations. The proposed PBS exhibits tolerance in width variation, and the polarization extinction ratios remain higher than 20 dB for both polarizations when the width variation is adjusted from + 10 to -10 nm. Benefiting from the enhanced coupling by the GACCs, the polarization extinction ratio can be kept higher than 15 dB and the insertion loss is lower than 2 dB for both polarizations when the coupling length varies from 30.96 to 13.76 μm.

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Understanding the motility behavior of bacteria in confining microenvironments, in which they search for available physical space and move in response to stimuli, is important for environmental, food industry, and biomedical applications. We studied the motility of five bacterial species with various sizes and flagellar architectures (Vibrio natriegens, Magnetococcus marinus, Pseudomonas putida, Vibrio fischeri, and Escherichia coli) in microfluidic environments presenting various levels of confinement and geometrical complexity, in the absence of external flow and concentration gradients. When the confinement is moderate, such as in quasi-open spaces with only one limiting wall, and in wide channels, the motility behavior of bacteria with complex flagellar architectures approximately follows the hydrodynamics-based predictions developed for simple monotrichous bacteria. Specifically, V. natriegens and V. fischeri moved parallel to the wall and P. putida and E. coli presented a stable movement parallel to the wall but with incidental wall escape events, while M. marinus exhibited frequent flipping between wall accumulator and wall escaper regimes. Conversely, in tighter confining environments, the motility is governed by the steric interactions between bacteria and the surrounding walls. In mesoscale regions, where the impacts of hydrodynamics and steric interactions overlap, these mechanisms can either push bacteria in the same directions in linear channels, leading to smooth bacterial movement, or they could be oppositional (e.g., in mesoscale-sized meandered channels), leading to chaotic movement and subsequent bacterial trapping. The study provides a methodological template for the design of microfluidic devices for single-cell genomic screening, bacterial entrapment for diagnostics, or biocomputation.