Artificial Bacterial Flagella Research Articles

Enhancing Swimming Performance of Magnetic Helical Microswimmers by Surface Microstructure.

Artificial bacterial flagella (ABF), also known as a magnetic helical microswimmer, has demonstrated enormous potential in various future biomedical applications (e.g., targeted drug delivery and minimally invasive surgery). Nevertheless, when used for in vivo/in vitro treatment applications, it is essential to achieve the high motion efficiency of the microswimmers for rapid therapy. In this paper, inspired by microorganisms, the surface microstructure was introduced into ABFs to investigate its effect on the swimming behavior. It was confirmed that compared with smooth counterparts, the ABF with surface microstructure reveals a smaller forward velocity below the step-out frequency (i.e., the frequency corresponding to the maximum velocity) but a larger maximum forward velocity and higher step-out frequency. A hydrodynamic model of microstructured ABF is employed to reveal the underlying movement mechanism, demonstrating that the interfacial slippage and the interaction between the fluid and the microstructure are essential to the swimming behavior. Furthermore, the effect of surface wettability and solid fraction of microstructure on the swimming performance of ABFs was investigated experimentally and analytically, which further reveals the influence of surface microstructure on the movement mechanism. The results present an effective approach for designing fast microrobots for in vivo/in vitro biomedical applications.

Wet metallization of 3D printed microarchitectures: Application to the manufacturing of bioinspired microswimmers

Untethered microswimmers have been recently proposed as possible candidates for a wealth of biomedical and environmental applications. In view of their translation from laboratory experimentation to clinical practice, it is fundamental to identify low-cost, scalable and flexible manufacturing approaches. The production method explored in the present paper, which responds to all these requirements, consists of a smart combination of two-photon lithography (2PL) and wet metallization. Fully functional bioinspired artificial bacterial flagella (ABFs) are successfully 3D printed following a user-defined model and made magnetically active by depositing a layer of CoNiP alloy on their surface via electroless deposition. In contrast with existing ABFs metallization approaches based on metal evaporation, electroless deposition does not suffer from the shadowing effect, and it can be employed to easily plate hard-magnetic alloys. The specific challenges of the application of electroless plating to the metallization of 2PL printed polymeric templates are identified, discussed and addressed. The manuscript also explores the possibility to impart multiple functionalities to the 3D printed microstructures by applying multiple metallic layers on their surface. Besides the applicative example of ABFs, the metallization methodology presented can be potentially used for the metallization of a great variety of 2PL printed microarchitectures for many possible applications.

Self-propelled nanofluids a coolant inspired from nature with enhanced thermal transport properties

Self-propelled nanofluids (SPNFs), are suspensions that contain active particles, that self-propel by converting some form of energy to mechanical work. This theoretical investigation considers the heat transfer mechanisms that may exist in an SPNF. Equations describing the effective mass diffusivity of spherical and rod-shaped particles were taken from the literature and used in analysis of particles of different shapes, aspect ratios, swimming velocities and suspended in water and in ethylene glycol. The analysis showed that the effective mass diffusivity of the particles was up to three orders of magnitude higher than the thermal diffusivity of the solvent. The enhancement of the mass diffusivity leads to a significant enhancement of thermal conductivity of up to an order of magnitude higher compared to that of the pure solvent. It is further discussed that in SPNFs, dispersion and clustering of particles and active turbulence mechanisms may add extra enhancement to the thermal transport. Recent experimental investigations supporting our findings are discussed. Combining this enhancement in thermal transport with the reported reduction of the viscosity observed for an SPNF consisting of Artificial Bacterial Flagella (ABF) particles, will help to create a highly efficient coolant. This can help to reduce energy consumption in a wide variety of the economic sectors, especially in the computing and data storage.

Surface-Chemistry-Mediated Control of Individual Magnetic Helical Microswimmers in a Swarm.

Magnetic helical microswimmers, also known as artificial bacterial flagella (ABFs), perform 3D navigation in various liquids under low-strength rotating magnetic fields by converting rotational motion to translational motion. ABFs have been widely studied as carriers for targeted delivery and release of drugs and cells. For in vivo/ in vitro therapeutic applications, control over individual groups of swimmers within a swarm is necessary for several biomedical applications such as drug delivery or small-scale surgery. In this work, we present the selective control of individual swimmers in a swarm of geometrically and magnetically identical ABFs by modifying their surface chemistry. We confirm experimentally and analytically that the forward/rotational velocity ratio of ABFs is independent of their surface coatings when the swimmers are operated below their step-out frequency (the frequency requiring the entire available magnetic torque to maintain synchronous rotation). We also show that ABFs with hydrophobic surfaces exhibit larger step-out frequencies and higher maximum forward velocities compared to their hydrophilic counterparts. Thus, selective control of a group of swimmers within a swarm of ABFs can be achieved by operating the selected ABFs at a frequency that is below their step-out frequencies but higher than the step-out frequencies of unselected ABFs. The feasibility of this method is investigated in water and in biologically relevant solutions. Selective control is also demonstrated inside a Y-shaped microfluidic channel. Our results present a systematic approach for realizing selective control within a swarm of magnetic helical microswimmers.

Self-propelled nanofluids a path to a highly effective coolant

We propose a new self-propelled nanofluid having advantageous thermal and rheological properties at the same time. The nanofluid consists of a low volume fraction of self-propelled particles known as Artificial Bacterial Flagella (ABF), which will swim as pushers in a manner similar to the swimming of E. coil microorganisms with flagella. A theoretical model is introduced, describing the mechanisms responsible for the reduction of viscosity. The model shows that the swimming velocity of the particle and its geometry play an essential role in the reduction of the suspension viscosity. The results obtained from the theoretical model compare qualitatively with experiments in the literature. The model shows a significant decrease in viscosity at very low volume fractions, and that the viscosity of the suspension is reduced as the volume fraction of the particles increases. Using an in-house finite volume code, we numerically simulate natural convection effects in our ABF self-propelled nanofuid inside a square cavity heated from its vertical sides. Simulations are conducted at volume fractions of 0.7%, 0.8% and 0.83%, comparing the performance of a self-propelled nanofluid with conventional non-active nanofluids (i.e. carbon nanotubes in water). The results show that the heat transfer rate measured by the Nusselt number is three times higher than for the case of classical nanofluids and pure water at the same operating conditions and 0.83% volume fraction of particles. Also, due to the very dilute volume fractions of particles in the proposed nanofluid, their stability can endure for long operating times. There is also a significant decrease in the viscosity (around 25 times lower than water) which will result in a significant reduction in the pumping power.

Magnetic Helical Microswimmers Functionalized with Lipoplexes for Targeted Gene Delivery

Artificial micro‐/nanoswimmers have various potential applications including minimally invasive diagnosis and targeted therapies, environmental sensing and monitoring, cell manipulation and analysis, and lab‐on‐a‐chip devices. Inspired by natural motile bacteria such as E. Coli, artificial bacterial flagella (ABFs) are one kind of magnetic helical microswimmers. ABFs can perform 3D navigation in a controllable fashion with micrometer precision under low‐strength rotating magnetic fields (<10 mT) and are promising tools for targeted drug delivery in vitro and in vivo. In this work, the successful wirelessly targeted and single‐cell gene delivery to human embryonic kidney (HEK 293) cells using ABFs loaded with plasmid DNA (pDNA) in vitro is demonstrated for the first time. The ABFs are functionalized with lipoplexes containing pDNA to generate functionalized ABFs (f‐ABFs). The f‐ABFs are steered wirelessly by low‐strength rotating magnetic fields and deliver the loaded pDNA into targeted cells. The cells targeted by f‐ABFs are successfully transfected by the transported pDNA and expressed the encoding protein. These f‐ABFs may also be useful for in vivo gene delivery and other applications such as sensors, actuators, cell biology, and lab‐on‐a‐chip environments.

Magnetic polymer composite artificial bacterial flagella

Artificial bacterial flagella (ABFs) are magnetically actuated swimming microrobots inspired by Escherichia coli bacteria, which use a helical tail for propulsion. The ABFs presented are fabricated from a magnetic polymer composite (MPC) containing iron-oxide nanoparticles embedded in an SU-8 polymer that is shaped into a helix by direct laser writing. The paper discusses the swim performance of MPC ABFs fabricated with varying helicity angles. The locomotion model presented contains the fluidic drag of the microrobot, which is calculated based on the resistive force theory. The robot’s magnetization is approximated by an analytical model for a soft-magnetic ellipsoid. The helicity angle influences the fluidic and magnetic properties of the robot, and it is shown that weakly magnetized robots prefer a small helicity angle to achieve corkscrew-type motion.

Artificial Bacterial Flagella for Remote‐Controlled Targeted Single‐Cell Drug Delivery

An approach for batch preparation of liposome-functionalized microdevices is demonstrated for remotely controlled single-cell drug delivery. The liposome functionalized artificial bacterial flagella exhibit corkscrew swimming in 3D with micrometer positioning precision by applying an external rotating magnetic field. The devices are also capable of delivering water-soluble drugs to single cells in vitro.

Artificial bacterial flagella functionalized with temperature-sensitive liposomes for controlled release

Inspired by flagellar propulsion of bacteria such as E. coli, artificial bacterial flagella (ABFs) are magnetic swimming microrobots with helical shapes. ABFs are capable of performing precise three-dimensional (3D) navigation in fluids under low-strength rotating magnetic fields making them attractive tools for targeted drug delivery. Further biomedical functionalization of these swimming microrobots is essential to enhance their biological and medical performances. We report the successful functionalization of titanium-coated ABFs with temperature-sensitive dipalmitoylphosphatidylcholine (DPPC)-based liposomes, known as “smart” drug carriers. Liposome coating on the surface of ABFs was confirmed using quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescent probes. The functionalized ABFs (f-ABFs) showed the ability to incorporate both hydrophilic and hydrophobic drugs. Finally, thermally triggered release of calcein (a common drug analog) from f-ABFs was demonstrated. These f-ABFs have the potential to be used in targeted and triggered drug delivery, microfluidic devices and biosensing.

Noncytotoxic artificial bacterial flagella fabricated from biocompatible ORMOCOMP and iron coating

Magnetic microrobots have potential use in biomedical applications such as minimally invasive surgery, targeted diagnosis and therapy. Inspired by nature, artificial bacterial flagella (ABFs) are a form of microrobot powered by magnetic helical propulsion. For the promise of ABFs to be realized, issues of biocompatibility must be addressed and the materials used in their fabrication should be carefully considered. In this work, we fabricate the helical bodies of ABFs from a commercially available biocompatible photoresist, ORMOCOMP, by subsequently coating them with Fe for magnetic actuation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays show that Fe-coated ORMOCOMP layers do not undermine the cell viability during 72 hours of incubation compared to control substrates. Cells exhibit normal morphology on ABF arrays and show good lamellipodial and filopodial interactions with the ABF surfaces. The swimming performance of Fe-coated ABFs is characterized using a three-pair Helmholtz coil arrangement. ABFs exhibit a maximum forward speed of 48.9 μm s-1 under a field of 9 mT at a frequency of 72 Hz. In summary, our Fe-coated ABFs exhibit little cytotoxicity and have potential for in vivo applications, especially those involving difficult to access regions within the human body.

Localized non-contact manipulation using artificial bacterial flagella

Artificial bacterial flagella (ABFs) are swimming microrobots that mimic the propulsion method of bacteria, such as Escherichia coli. Microrobots have the potential to act as wireless manipulation tools for invitro applications. This paper investigates the micro-flows induced by ABFs for localized contact-free manipulation of micro-objects. The flow is simulated using the method of fundamental solutions and compared to experimental data where the tangential flow was measured by means of tracking polystyrene microbeads. Good agreement with the experimental data was found, and preliminary results show the contact-free rotation away from and the translation of micro-objects near a solid wall.

Artificial bacterial flagella for micromanipulation

This article presents an overview of recent developments in artificial bacterial flagella (ABFs) and discusses challenges and opportunities in pursuing applications. These helical swimmers possess several advantageous characteristics, such as high swimming velocity and precise motion control indicating their potential for diverse applications. One application is the manipulation of small objects within liquid, which is the focus of this review. Preliminary results have shown that ABFs are capable of performing microobject manipulation either directly by mechanical contact or indirectly by generating a localized fluid flow. The latter approach can be used for batch manipulation without direct contact, also implying possibilities for flow control in lab-on-a-chip systems. Miniaturized helical swimmers are also promising for biomedical applications, such as targeted drug delivery and implantation or removal of tissues and other objects.

Rolled-up helical nanobelts: from fabrication to swimming microrobots

AbstractWe present recent developments in rolled-up helical nanobelts in which helical structures are fabricated by the self-scrolling technique. Nanorobotic manipulation results show that these structures are highly flexible and mechanically stable. Inspired by the helical-shaped flagella of motile bacteria, such as E. coli, artificial bacterial flagella (ABFs) are a new type of swimming microrobot. Experimental investigation shows that the motion, force, and torque generated by an ABF can be precisely controlled using a low-strength, rotating magnetic field. These miniaturized helical swimming microrobots can be used as magnetically driven wireless manipulators for manipulation of microobjects in fluid and for target drug delivery.

Characterizing the Swimming Properties of Artificial Bacterial Flagella

Artificial bacterial flagella (ABFs) consist of helical tails resembling natural flagella fabricated by the self-scrolling of helical nanobelts and soft-magnetic heads composed of Cr/Ni/Au stacked thin films. ABFs are controlled wirelessly using a low-strength rotating magnetic field. Self-propelled devices such as these are of interest for in vitro and in vivo biomedical applications. Swimming tests of ABFs show a linear relationship between the frequency of the applied field and the translational velocity when the frequency is lower than the step-out frequency of the ABF. Moreover, the influences of head size on swimming velocity and the lateral drift of an ABF near a solid boundary are investigated. An experimental method to estimate the propulsion matrix of a helical swimmer under a light microscope is developed. Finally, swarm-like behavior of multiple ABFs controlled as a single entity is demonstrated.

Artificial bacterial flagella: Fabrication and magnetic control

Inspired by the natural design of bacterial flagella, we report artificial bacterial flagella (ABF) that have a comparable shape and size to their organic counterparts and can swim in a controllable fashion using weak applied magnetic fields. The helical swimmer consists of a helical tail resembling the dimensions of a natural flagellum and a thin soft-magnetic “head” on one end. The swimming locomotion of ABF is precisely controlled by three orthogonal electromagnetic coil pairs. Microsphere manipulation is performed, and the thrust force generated by an ABF is analyzed. ABF swimmers represent the first demonstration of microscopic artificial swimmers that use helical propulsion. Self-propelled devices such as these are of interest in fundamental research and for biomedical applications.