Jamel Ali

Low aspect ratio micropores for single-particle and single-cell analysis

This paper describes microparticle and bacterial translocation studies using low aspect ratio solid‐state micropores. Micropores, 5 μm in diameter, were fabricated in 200 nm thick free‐standing silicon nitride membranes, resulting in pores with an extremely low aspect ratio, nominally 0.04. For microparticle translocation experiments, sulfonated polystyrene microparticles and magnetic microbeads in size range of 1–4 μm were used. Using the microparticle translocation characteristics, we find that particle translocations result in a change only in the pores geometrical resistance while the access resistance remains constant. Furthermore, we demonstrate the ability of our micropore to probe high‐resolution shape information of translocating analytes using concatenated magnetic microspheres. Distinct current drop peaks were observed for each microsphere of the multibead architecture. For bacterial translocation experiments, nonflagellated Escherichia coli (strain HCB 5) and wild type flagellated Salmonella typhimurium (strain SJW1103) were used. Distinct current signatures for the two bacteria were obtained and this difference in translocation behavior was attributed to different surface protein distributions on the bacteria. Our findings may help in developing low aspect ratio pores for high‐resolution microparticle characterization and single‐cell analysis.

Investigation of bacterial chemotaxis using a simple three-point microfluidic system

A three-point microfluidic system was developed and used to experimentally verify bacterial chemotaxis with known chemoeffectors. Using pneumatically-controlled micro-valves, the device was able to regulate microscale flows and created concentration gradients that allowed GFP-labelled Escherichia coli cells to interact with an environment that contained a chemoattractant and a chemorepellent. Having two separate possible paths (left and right) for the bacteria to move forward, this device also allowed for imaging processing based removal of noisy data, if adirectional bias was present. This device could be useful for quantitative analysis of chemotactic behaviors with minimal technical requirements, and could motivate the development of future devices based on this concept.

Bacteria-inspired nanorobots with flagellar polymorphic transformations and bundling

Wirelessly controlled nanoscale robots have the potential to be used for both in vitro and in vivo biomedical applications. So far, the vast majority of reported micro- and nanoscale swimmers have taken the approach of mimicking the rotary motion of helical bacterial flagella for propulsion, and are often composed of monolithic inorganic materials or photoactive polymers. However, currently no man-made soft nanohelix has the ability to rapidly reconfigure its geometry in response to multiple forms of environmental stimuli, which has the potential to enhance motility in tortuous heterogeneous biological environments. Here, we report magnetic actuation of self-assembled bacterial flagellar nanorobotic swimmers. Bacterial flagella change their helical form in response to environmental stimuli, leading to a difference in propulsion before and after the change in flagellar form. We experimentally and numerically characterize this response by studying the swimming of three flagellar forms. Also, we demonstrate the ability to steer these devices and induce flagellar bundling in multi-flagellated nanoswimmers.

On-Surface Locomotion of Particle Based Microrobots Using Magnetically Induced Oscillation

The low Reynolds number condition presents a fundamental constraint on designing locomotive mechanisms for microscale robots. We report on the use of an oscillating magnetic field to induce on-surface translational motion of particle based microrobots. The particle based microrobots consist of microparticles, connected in a chain-like manner using magnetic self-assembly, where the non-rigid connections between the particles provide structural flexibility for the microrobots. Following the scallop theorem, the oscillation of flexible bodies can lead to locomotion at low Reynolds numbers, similar to the beating motion of sperm flagella. We characterized the velocity profiles of the microrobots by measuring their velocities at various oscillating frequencies. We also demonstrated the directional steering capabilities of the microrobots. This work will provide insights into the use of oscillation as a viable mode of locomotion for particle based microrobots near a surface.

Fabrication and magnetic control of alginate-based rolling microrobots

Advances in microrobotics for biological applications are often limited due to their complex manufacturing processes, which often utilize cytotoxic materials, as well as limitations in the ability to manipulate these small devices wirelessly. In an effort to overcome these challenges, we investigated a facile method for generating biocompatible hydrogel based robots that are capable of being manipulated using an externally generated magnetic field. Here, we experimentally demonstrate the fabrication and autonomous control of loaded-alginate microspheres, which we term artificial cells. In order to generate these microparticles, we employed a centrifuge-based method in which microspheres were rapidly ejected from a nozzle tip. Specifically, we used two mixtures of sodium alginate; one containing iron oxide nanoparticles and the other containing mammalian cells. This mixture was loaded into a needle that was fixed on top of a microtube containing calcium chloride, and then briefly centrifuged to generate hundreds of Janus microspheres. The fabricated microparticles were then magnetically actuated with a rotating magnetic field, generated using electromagnetic coils, prompting the particles to roll across a glass substrate. Also, using vision-based feedback control, a single artificial cell was manipulated to autonomously move in a programmed pattern.

Micro Manipulation Using Magnetic Microrobots

When developing microscale robotic systems it is desired that they are capable of performing microscale tasks such as small scale manipulation and transport. In this paper, we demonstrate the transport of microscale objects using single or multiple microrobots in low Reynolds number fluidic environment. The microrobot is composed of a ‘U’ shaped SU-8 body, coated on one side with nickel. Once the nickel coating is magnetized, the motion of the microrobots can be driven by external magnetic fields. To invoke different responses from two microrobots under a global magnetic field, two batches of microrobots were fabricated with different thicknesses of nickel coating as a way to promote heterogeneity within the microrobot population. The heterogeneity in magnetic content induces different spatial and temporal responses under the same control input, resulting in differences in movement speed. The nickel coated microstructure is manually controlled through a user interface developed using C++. This paper presents a control strategy to navigate the microrobots by controlling the direction and strength of externally applied magnetic field, as well as orientation of the microrobots based on their polarity. In addition, multiple microrobots are used to perform transport tasks.

Biotemplated flagellar nanoswimmers

In this article, a porous hollow biotemplated nanoscale helix that can serve as a low Reynolds number robotic swimmer is reported. The nanorobot utilizes repolymerized bacterial flagella from Salmonella typhimurium as a nanotemplate for biomineralization. We demonstrate the ability to generate templated nanotubes with distinct helical geometries by using specific alkaline pH values to fix the polymorphic form of flagellar templates. Using uniform rotating magnetic fields to mimic the motion of the flagellar motor, we explore the swimming characteristics of these silica templated flagella and demonstrate the ability to wirelessly control their trajectories. The results suggest that the biotemplated nanoswimmer can be a cost-effective alternative to the current top-down methods used to produce helical nanorobots.