We are an interdisciplinary experimental group that is developing microbiorobotics, nano/microfluidics, and nanopore technologies for biological applications.

ongoing research program can be broadly categorized into three core subject areas: micro/nanorobotics, single cell/single molecule biophysics, and transport phenomena. Although each core program consists of a distinct project, we would like to emphasize their synergistic nature – advances in one core are expected to drive the development of the others. The unifying component of all the cores is “biologically inspired nano/micro engineering.”

Rapid advances in science and engineering over the past 20 years have enabled us to manipulate matter down to the atomic level. With this unprecedented level of control over matter extraordinary new technologies are being developed with applications spanning a diverse array of fields ranging from biology to robotics. Today there exist a diversity range of nano/microfabrication techniques that are capable of producing small scale functional materials and devices. These new stimuli responsive devices open up the possibility to probe biology on the length scales where fundamental biological processes take place, such as epigenetic and genetic control of single cells. Currently our lab is actively researching four broad topics revolving around small scale engineering: Microbiorobotics for Manipulation and Sensing, Synthetic Nanopore Fabrication and Single Molecule/Single Cell Analysis, Biologically Inspired Metamaterials for Nano/Optoelectronics, and Swimming and Flying at Low Reynold Number.

We are always happy to work with motivated students who have a passion for research. If you are interested in joining our lab, it is recommended that you kindly email Professor MinJun Kim to talk about your qualification and research interest as early as possible.

 

Research Thrust #1: Microbiorobotics for Manipulation and Sensing

Microrobotics offer the possibilities for many applications including in micromanipulation and microfabrication, drug delivery, and minimally invasive surgery. To overcome challenges of low Reynolds number dynamics in viscous and viscoelastic fluids, BAST lab works at the interface between microbiology and robotics to create three categories of nature inspired microrobots: the achiral microswimmers, the bacterial-powered hybrid microbiorobots, and magnetotactic cellular microrobots. These microscale robots had demonstrated low Reynolds number navigation, microscale assembly, and automatous control.

RT1_achiral

The magnetically actuated achiral microswimmer consists of 3-beads rigidly linked using biotin-avidin chemistry. This swimmer is capable of converting rotating motion into translational motion in bulk fluid at low Reynolds number without the commonly regarded conditions of flexibility or chiral geometry. The achiral swimmers are actuated wirelessly using an external rotating magnetic field supplied by approximate Helmholtz coils. The achiral microswimmers exhibited active propulsion and were controllable in both speed and direction. We are currently working on multiple robot control to manipulate a team of microswimmers as a viable workforce and modular microrobotics for dynamic adaptability to heterogeneity environments.

RT1_MBR

Flagellated bacteria are integrated with engineered systems to construct bacterial-powered hybrid microbiorobots (MBRs). MBRs are microfabricated SU-8 epoxy structures with typical feature sizes ranging from 5 – 100 microns coated with a monolayer of the swarming Serratia marcescens, where the adherent bacterial cells naturally coordinate to propel the microstructures in fluidic environments. We explore some design aspects, such as the effects of bacterial density, distribution and orientation on the surface of the MBRs, as well as various modalities to control the bacteria. A number of different stimuli, including ultraviolet light, electric field, chemotactic gradient, and thermal stimuli are used as control inputs to manipulate the MBRs into performing sample tasks since as cargo transport and microassembly.

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The magnetotactic cellular microrobot fuses micro-scale inorganic components with cellular actuators for object manipulation which is a great challenge in micro-scale robotics (length scale of 1 micron to 1 mm). Specifically, we are fusing inorganic actuators onto live microbial cells so as to use them as micro-scale robots, essentially creating what we call “micro-cyborgs”. Our approach in fusing inorganic actuators and biological actuators constitutes a novel direction in microbiorobotics. Currently, researchers have explored separate use of bio-inspired engineered structures (such as artificial flagella) and live cells (such as bacterial swimmers) as micro-scale actuators. In this research, we seek to combine the merits of both types of actuators, e.g. repeatability and specificity of inorganic actuators and low cost of biological actuators. The biological part of our micro-cyborg is an artificially magnetotactic Tetrahymena pyriformis. Joint use of multiple micro-cyborgs can result in manipulation of larger objects. The range of operation of micro-cyborgs makes them potentially useful in biomedical applications (e.g. cell manipulation) and micro-assembly.

 

Research Thrust #2: Synthetic Nanopore Fabrication and Single Molecule Analysis

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The translocation of analytes through nanometer-sized pores in solid-state or biological membranes has attracted significant attention over the last decade, in both academia and industry. The key idea is to monitor the ionic current across a nanopore, and to associate any transient modulation of it (resistive/conductive pulse) to the translocation of a molecular species through the pore. The resulting “signature” in the current may then be used for probing the biomolecule itself. The aim of our nanopore research is to define a new nanoanalytical technology which will enable efficient detection of conformational changes with microsecond resolution in order to answer a fundamental question about structure and conformations of proteins, DNA molecules, or whole organisms (bacteria/viruses). It is achieved by electrophoretically translocating bioanalytes through a solitary nanopore drilled in thin silicon nitride membrane and analyzing their corresponding current signatures. This has enabled us to study binding-unbinding and folding-unfolding kinetics of single protein molecules. In addition, we have developed DNA sensing platform based on graphene nanopores drilled in single or multi-layer graphene structures which provide exquisite control of the electric field drop within the pore. Nanopore edges are modified with Graphite Polyhydral Crystals (GPC) and the modified GPC nanopores can be used to sense small DNA molecules (down to 25 nucleotide long) which is a significant improvement in the sensing ability of solid-state nanopores. Lastly, we are developing smart solid-state nanopore and nanopore array with superior chemical and mechanical robustness and pore size variability as ultra-fast high throughput nanopore sensors for biophysical characterization of viruses, bacteria and cells with single-cell or single-particle resolution.

 

Research Thrust #3: Biologically Inspired Metamaterials for Nano/Optoelectronics

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Proteins are natural polymers that are the basic building blocks of all life. Many proteins have the ability to form higher ordered structures by self-assembly. One such protein is flagellin, which self assembles to form bacterial flagella. Specifically, in our research we have been studying the unique properties of bacterial flagellar nanotubes and the possibility to exploit them for use in nanoscale sensing devices. Of particular interest to our research group is the ability to use these molecules either in their naive or genetically modified forms to fabricate engineered micro- and nanosystems. Our research is focused on understanding the fundamental scientific principles that govern the polymorphic transformation of bacterial flagellar nanotubes, both in loaded and unloaded conditions, due to chemical, thermal, and electrical stimulation, as well as to demonstrate the enabling technologies necessary to develop mineralization and metalization of flagellar nanotubes for nanoelectronic sensing devices. In addition to organic based nano systems, we are also investigating the use of inorganic gold nanorods (GNRs) to eradicate surface-bound infectious pathogens through photon-to-thermal energy conversion. The most distinctive advantage of this photothermal disinfection method is that it will not cause any cross resistance with antibiotic or build up antimicrobial resistance in the environment. Through near infrared evanescent wave irradiation, disinfection of a large surface area can be achieved conveniently and energy-efficiently. Specifically, targeted applications of this technology include reducing bloodstream infections in hospitalized patients during their continuous use of medical catheters and creating safe, self-sterilizing touchscreen computers for use in public areas.

 

Research Thrust #4: Swimming at Low Reynolds Number: Many microorganisms swim

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Swimming at Low Reynolds Number: Many microorganisms swim through complex biomaterials, including sperm travelling through mucous in the female reproductive tract and bacteria penetrating mucus layers in the respiratory and digestive tracts during infection and disease. Because the scale of microstructural features in such media can be similar to the size of microbes, microbial transport through these biomaterials is a complicated multiscale problem. At the microscale, mechanical deformation, long- and short-range hydrodynamic forces, and contact forces can all potentially influence microbial swimming. Macroscale transport through biomaterials depends on swimming speed and adhesion lifetimes mediated by all these microscale interactions. To address the challenges in microscale swimming, low Reynolds number microswimmers have been fabricated and successfully controlled. Three dimensional Helmholtz coils are used for precise control of microswimmers. By setting our goal on biomedical applications such as targeted and localized drug delivery, we maintain paramount investigations in the field of microswimming in complex media.

Flapping Wing Flight: By thoroughly studying the aerodynamics of beetle flight, it is possible to bleach the limitations in developing micro/nano aerial vehicles, specifically the difficulties to fabricate an assortment of machinery parts and and developing miniaturized power sources. Our research is focused on characterizing the flapping wing kinematics and aerodynamics of beetles. Key interest lies in the beetles’ ability for non-jumping take-off and hovering flight. The final goal of this research is to develop beetle cyborgs with the extraordinary flight characteristics of the beetles.

 

Past Research Projects

– Fabrication of Single-digit Nanometer Solid-state Pore for Single Molecule Analysis

– Bacterial Flows: Mixing and Pumping in Microfluidic Systems Using Flagellated Bacteria

– Microfluidic Flow Control Using Electroosmosis