Engineering Approaches to Biomanipulation

Electromagnetic Forces and Torques: From Dielectrophoresis to Optical Tweezers

Electromagnetic forces and torques enable many key technologies, including optical tweezers or dielectrophoresis. Interestingly, both techniques rely on the same physical process: the interaction of an oscillating electric field with a particle of matter. This work provides a unified framework to understand this interaction both when considering fields oscillating at low frequencies─dielectrophoresis─and high frequencies─optical tweezers. We draw useful parallels between these two techniques, discuss the different and often unstated assumptions they are based upon, and illustrate key applications in the fields of physical and analytical chemistry, biosensing, and colloidal science.

Multimodal Bubble Microrobot Near an Air-Water Interface

The development of multifunctional and robust swimming microrobots working at the free air-liquid interface has encountered challenge as new manipulation strategies are needed to overcome the complicated interfacial restrictions. Here, flexible but reliable mechanisms are shown that achieve a remote-control bubble microrobot with multiple working modes and high maneuverability by the assistance of a soft air-liquid interface. This bubble microrobot is developed from a hollow Janus microsphere (JM) regulated by a magnetic field, which can implement switchable working modes like pusher, gripper, anchor, and sweeper. The collapse of the microbubble and the accompanying directional jet flow play a key role for functioning in these working modes, which is analogous to a "bubble tentacle." Using a simple gamepad, the orientation and the navigation of the bubble microrobot can be easily manipulated. In particular, a speed modulation method is found for the bubble microrobot, which uses vertical magnetic field to control the orientation of the JM and the direction of the bubble-induced jet flow without changing the fuel concentration. The findings demonstrate a substantial advance of the bubble microrobot specifically working at the air-liquid interface and depict some nonintuitive mechanisms that can help develop more complicated microswimmers.

3D-Printed Micro-Tweezers with a Compliant Mechanism Designed Using Topology Optimization

The development of handling technology for microscopic biological samples such as cells and spheroids has been required for the advancement of regenerative medicine and tissue engineering. In this study, we developed micro-tweezers with a compliant mechanism to manipulate organoids. The proposed method combines high-resolution microstereolithography that uses a blue laser and topology optimization for shape optimization of micro-tweezers. An actuation system was constructed using a linear motor stage with a force control system to operate the micro-tweezers. The deformation of the topology-optimized micro-tweezers was examined analytically and experimentally. The results verified that the displacement of the tweezer tip was proportional to the applied load; furthermore, the displacement was sufficient to grasp biological samples with an approximate diameter of several hundred micrometers. We experimentally demonstrated the manipulation of an organoid with a diameter of approximately 360 µm using the proposed micro-tweezers. Thus, combining microstereolithography and topology optimization to fabricate micro-tweezers can be potentially used in modifying tools capable of handling various biological samples.

3D steerable, acoustically powered microswimmers for single-particle manipulation

The ability to precisely maneuver micro/nano objects in fluids in a contactless, biocompatible manner can enable innovative technologies and may have far-reaching impact in fields such as biology, chemical engineering, and nanotechnology. Here, we report a design for acoustically powered bubble-based microswimmers that are capable of autonomous motion in three dimensions and selectively transporting individual synthetic colloids and mammalian cells in a crowded group without labeling, surface modification, or effect on nearby objects. In contrast to previously reported microswimmers, their motion does not require operation at acoustic pressure nodes, enabling propulsion at low power and far from an ultrasonic transducer. In a megahertz acoustic field, the microswimmers are subject to two predominant forces: the secondary Bjerknes force and a locally generated acoustic streaming propulsive force. The combination of these two forces enables the microswimmers to independently swim on three dimensional boundaries or in free space under magnetical steering.

Effect of Injection Speed on Oocyte Deformation in ICSI

Oocyte deformation during injection is a major cause of potential cell damage which can lead to failure in the Intracytoplasmic Sperm Injection (ICSI) operation used as an infertility treatment. Injection speed plays an important role in the deformation creation. In this paper the effect of different speeds on deformation of zebrafish embryos is studied using a specially designed experimental set-up. An analytical model is developed in order to link injection force, deformation, and injection speed. A finite element (FE) model is also developed to analyse the effect of injection speed, allowing the production of additional information that is difficult to obtain experimentally, e.g., deformation and stress fields on the oocyte. The numerical model is validated against experimental results. Experimental results indicate that by increasing the injection speed, the deformation decreases. However, higher speeds cause higher levels of injection force and force fluctuation, leading to a higher vibration during injection. For this reason, an optimum injection speed range is determined. Finally, the FE model was validated against experimental results. The FE model is able to predict the force-deformation variation during injection for different speeds. This proves to be useful for future studies investigating different injection conditions.

Phase-shift feedback control for dielectrophoretic micromanipulation

In this paper, we present a novel approach to noncontact micromanipulation by controlled dielectrophoresis (DEP). To steer micro-objects in the desired way, the solutions reported in the literature use either DEP cages or amplitude modulation of the voltages applied to the electrodes. In contrast, we modulate the phases, that is, we control the phase shifts of the voltages applied to the electrodes, which simplifies the hardware implementation and extends the set of feasible forces. Furthermore, we introduce an innovative micro-electrode array layout, composed of four sectors with parallel (colinear) electrodes, which is capable of inducing an arbitrary movement in the manipulation area and is easy to fabricate using just an affordable one-layer technology. We then propose a closed-loop cascade control strategy based on real-time numerical optimization and deploy it to our experimental set-up. Numerical simulations and laboratory experiments demonstrate the manipulation capabilities such as positioning and steering of one or several microscopic objects (microspheres with a diameter of 50 μm) and even bringing two objects together and then separating them again. The results from simulations and experiments are compared and the positioning accuracy is evaluated in the whole manipulation area. The error in position is 8 μm in the worst case, which corresponds to 16% of the microsphere size or 0.7% of the manipulation range.

Closed loop control of microscopic particles incorporating steady streaming and visual feedback

Automatic manipulation of microscopic particles is very important in biology, especially in new lab-on-chip systems for automatic testing and DNA manipulation. We suggest a particle manipulation system (PMS) based on vibrating piezoelectric beams creating steady streaming flow in a viscous liquid. The flow is nearly unidirectional and it is used to control the position and velocity of the particles in the workspace of the PMS. The particles position in the PMS are controlled by visual feedback. This study presents the manipulation method, the system's model describing its behavior and characterizes experimentally its performance. The PMS is capable moving a 2-200 μm particle in a workspace of 8x8 mm² with an absolute accuracy of 0.2 μm. The characteristic velocity in 500 cP Si oil, is 20 μm/s using an actuation voltage amplitude of 5 V and can reach 250 μm/s using 15 V respectively. We can also move a constellation of several particles in various sizes without changing the distance between them. The accuracy of the manipulation can be increased by enhancing the amplification of the microscope on the expanse of a smaller workspace field of view.

Non-conservative optical forces

Undoubtedly, laser tweezers are the most recognized application of optically induced mechanical action. Their operation is usually described in terms of conservative forces originating from intensity gradients. However, the fundamental optical action on matter is non-conservative. We will review different manifestations of non-conservative optical forces (NCF) and discuss their dependence on the specific spatial properties of optical fields that generate them. New developments relevant to the NCF such as tractor beams and transversal forces are also discussed.

Remotely Controlled Micromanipulation by Buckling Instabilities in Fe3O4 Nanoparticle Embedded Poly(N-isopropylacrylamide) Surface Arrays

The micromanipulation of biological samples is important for microbiology, pharmaceutical science, and related bioengineering fields. In this work, we report the fabrication and characterization of surface-attached microbeam arrays of 20 μm width and 25 μm height made of poly(N-isopropylacrylamide), a thermoresponsive polymer, with embedded spherical or octopod Fe₃O₄ nanoparticles. Below 32 °C, the microbeams imbibe water and buckle with an amplitude of approximately 20 μm. Turning on an AC-magnetic field induces the microbeam array to expel water due to the heating effect of the nanoparticles (magnetic hyperthermia), leading to a reversible transition from a buckled to nonbuckled state. It is observed that the octopod nanoparticles have a heating rate 30% greater (specific absorption rate, SAR) than that of the spherical nanoparticles, which shortens the time scale of the transition from the buckled and nonbuckled state. The return of the microbeams to the buckled state is accomplished by turning off the AC magnetic field, the rate of which is dictated by dissipation of heat and is independent of the type of nanoparticle. It is further demonstrated that this transition can be used to propel 50 μm spherical objects along a surface. While the motion is random, this study shows the promise of harnessing shape-shifting patterns in microfluidics for object manipulation.

Autofocusing and Polar Body Detection in Automated Cell Manipulation

Autofocusing and feature detection are two essential processes for performing automated biological cell manipulation tasks. In this paper, we have introduced a technique capable of focusing on a holding pipette and a mammalian cell under a bright-field microscope automatically, and a technique that can detect and track the presence and orientation of the polar body of an oocyte that is rotated at the tip of a micropipette. Both algorithms were evaluated by using mouse oocytes. Experimental results show that both algorithms achieve very high success rates: 100% and 96%. As robust and accurate image processing methods, they can be widely applied to perform various automated biological cell manipulations.

Medibots: Dual-Action Biogenic Microdaggers for Single-Cell Surgery and Drug Release

An innovative concept for the fabrication of dual-action microrobots capable of performing single-cell microsurgery along with a site-directed drug-delivery feature is presented. These multi-action plant-derived biocompatible "medibots" can play a pivotal role in understanding micromotor interactions at the cellular level, aiming toward the destruction of harmful cells (like cancer) among others in living systems.

Magnetically driven microrobotic system for cancer cell manipulation

Lab-on-a-chip applications, such as single cell manipulation and targeted delivery of chemicals, could greatly benefit from mobile untethered microdevices able to move in fluidic environments by using magnetic fields. In this paper a magnetically driven microrobotic system enabling the controlled locomotion of objects placed at the air/liquid interface is proposed and exploited for cell manipulation. In particular authors report the design, fabrication and testing of a polymeric thin film-based magnetic microrobot (called "FilmBot") used as a support for navigating cancer cells. By finely controlling magnetic film locomotion, it is possible to navigate the cells by exploiting their adhesion to the film without affecting their integrity. Preliminary in vitro tests demonstrated that the magnetic thin film is able to act as substrate for T24 bladder cancer cells without affecting their viability and that film locomotion can be magnetically controlled (with a magnetic field and a gradient of 6 mT and 0.6 T/m, respectively) along specific directions, with a mean speed of about 3 mm/s.

Intercalation-driven reversible control of magnetism in bulk ferromagnets

An extension in magnetoelectric effects is proposed to include reversible chemistry-controlled magnetization variations. This ion-intercalation-driven magnetic control can be fully reversible and pertinent to bulk material volumes. The concept is demonstrated for ferromagnetic iron oxide where the intercalated lithium ions cause valence change and partial redistribution of Fe(3+) cations yielding a large and fully reversible change in magnetization at room temperature.

Controlling magnetotactic bacteria through an integrated nanofabricated metallic island and optical microscope approach

Herein, we demonstrate the control of magnetotactic bacteria through the application of magnetic field gradients with real-time visualization. We accomplish this control by integrating a pair of macroscale Helmholtz coils and lithographically fabricated nanoscale islands composed of permalloy (Ni₈₀Fe₂₀). This system enabled us to guide and steer amphitrichous Magnetospirillum magneticum strain AMB-1 to specific location via magnetic islands. The geometries of the islands allowed us to have control over the specific magnetic field gradients on the bacteria. We estimate that magnetotactic bacteria located less than 1 μm from the edge of a diamond shaped island experience a maximum force of approximately 34 pN, which engages the bacteria without trapping them. Our system could be useful for a variety of applications including magnetic fabrication, self-assembly, and probing the sensing apparatus of magnetotactic bacteria.

Cooperative manipulation and transport of microobjects using multiple helical microcarriers

We report a cooperative transport strategy that uses engineered microbars and multiple helical microcarriers. Cooperation of microcarriers generates higher propulsive forces while application of forces at multiple locations results in motion control with multiple degrees of freedom.

Automated biomanipulation of single cells using magnetic microrobots

Transport of individual cells or chemical payloads on a subcellular scale is an enabling tool for the study of cellular communication, cell migration, and other localized phenomena. We present a magnetically actuated robotic system capable of fully automated manipulation of cells and microbeads. Our strategy uses autofluorescent robotic transporters and fluorescently labeled microbeads to aid tracking and control in optically obstructed environments. We demonstrate automated delivery of microbeads infused with chemicals to specified positions on neurons. This system is compatible with standard upright and inverted light microscopes and is capable of applying forces less than 1 pN for precision positioning tasks.

Transferring isolated mitochondria into tissue culture cells

We have developed a new method for introducing large numbers of isolated mitochondria into tissue culture cells. Direct microinjection of mitochondria into typical mammalian cells has been found to be impractical due to the large size of mitochondria relative to microinjection needles. To circumvent this problem, we inject isolated mitochondria through appropriately sized microinjection needles into rodent oocytes or single-cell embryos, which are much larger than tissue culture cells, and then withdraw a ‘mitocytoplast’ cell fragment containing the injected mitochondria using a modified holding needle. These mitocytoplasts are then fused to recipient cells through viral-mediated membrane fusion and the injected mitochondria are transferred into the cytoplasm of the tissue culture cell. Since mouse oocytes contain large numbers of mouse mitochondria that repopulate recipient mouse cells along with the injected mitochondria, we used either gerbil single-cell embryos or rat oocytes to package injected mouse mitochondria. We found that the gerbil mitochondrial DNA (mtDNA) is not maintained in recipient rho0 mouse cells and that rat mtDNA initially replicated but was soon completely replaced by the injected mouse mtDNA, and so with both procedures mouse cells homoplasmic for the mouse mtDNA in the injected mitochondria were obtained.

Formation of embryoid bodies using dielectrophoresis

Embryoid body (EB) formation forms an important step in embryonic stem cell differentiation invivo. In murine embryonic stem cell (mESC) cultures EB formation is inhibited by the inclusion of leukaemic inhibitory factor (LIF) in the medium. Assembly of mESCs into aggregates by positive dielectrophoresis (DEP) in high field regions between interdigitated oppositely castellated electrodes was found to initiate EB formation. Embryoid body formation in aggregates formed with DEP occurred at a more rapid rate-in fact faster compared to conventional methods-in medium without LIF. However, EB formation also occurred in medium in which LIF was present when the cells were aggregated with DEP. The optimum characteristic size for the electrodes for EB formation with DEP was found to be 75-100 microns; aggregates smaller than this tended to merge, whilst aggregates larger than this tended to split to form multiple EBs. Experiments with ESCs in which green fluorescent protein (GFP) production was targeted to the mesodermal gene brachyury indicated that differentiation within embryoid bodies of this size may preferentially occur along the mesoderm lineage. As hematopoietic lineages during normal development derive from mesoderm, the finding points to a possible application of DEP formed EBs in the production of blood-based products from ESCs.

Liver regenerative medicine: advances and challenges

Liver transplantation is the standard care for many end-stage liver diseases. However, donor organs are scarce and some people succumb to liver failure before a donor is found. Liver regenerative medicine is a special interdisciplinary field of medicine focused on the development of new therapies incorporating stem cells, gene therapy and engineered tissues in order to repair or replace the damaged organ. In this review we consider the emerging progress achieved in the hepatic regenerative medicine within the last decade. The review starts with the characterization of liver organogenesis, fetal and adult stem/progenitor cells. Then, applications of primary hepatocytes, embryonic and adult (mesenchymal, hematopoietic and induced pluripotent) stem cells in cell therapy of liver diseases are considered. Current advances and challenges in producing mature hepatocytes from stem/progenitor cells are discussed. A section about hepatic tissue engineering includes consideration of synthetic and natural biomaterials in engineering scaffolds, strategies and achievements in the development of 3D bioactive matrices and 3D hepatocyte cultures, liver microengineering, generating bioartificial liver and prospects for fabrication of the bioengineered liver.

Targeted cargo delivery using a rotating nickel nanowire

This paper reports an approach to perform basic noncontact and contact manipulation tasks using rotating nickel nanowires driven by a rotating magnetic field. A rotating nanowire is capable of propulsion and steering near a solid surface by a tumbling motion. The FEM simulation shows that fluid flow is induced around the rotating nanowire, which was applied to manipulate micro-objects in a noncontact fashion. Pushing, pulling, and rotation tests of individual polystyrene microbeads are conducted on a solid surface. In addition, targeted delivery tasks of biological samples, e.g., individual flagellated microorganisms and human blood cells, are demonstrated. The results imply that rotating magnetic nanowires are good tools for handling cellular and subcellular objects in an aqueous low-Reynolds-number environment and have potential for single-cell analysis.

FROM THE CLINICAL EDITOR

In this study, the authors report the ability to push, pull, and rotate individual polystyrene microbeads on a solid surface. Furthermore, they demonstrate targeted delivery of biological samples, implying that rotating magnetic nanowires are good tools for handling cellular and subcellular objects.

Magnetic domain wall conduits for single cell applications

The ability to trap, manipulate and release single cells on a surface is important both for fundamental studies of cellular processes and for the development of novel lab-on-chip miniaturized tools for biological and medical applications. In this paper we demonstrate how magnetic domain walls generated in micro- and nano-structures fabricated on a chip surface can be used to handle single yeast cells labeled with magnetic beads. In detail, first we show that the proposed approach maintains the microorganism viable, as proven by monitoring the division of labeled yeast cells trapped by domain walls over 16 hours. Moreover, we demonstrate the controlled transport and release of individual yeast cells via displacement and annihilation of individual domain walls in micro- and nano-sized magnetic structures. These results pave the way to the implementation of magnetic devices based on domain walls technology in lab-on-chip systems devoted to accurate individual cell trapping and manipulation.

On-chip magnetically actuated robot with ultrasonic vibration for single cell manipulations

This paper presents an innovative driving method for an on-chip robot actuated by permanent magnets in a microfluidic chip. A piezoelectric ceramic is applied to induce ultrasonic vibration to the microfluidic chip and the high-frequency vibration reduces the effective friction on the MMT significantly. As a result, we achieved 1.1 micrometre positioning accuracy of the microrobot, which is 100 times higher accuracy than without vibration. The response speed is also improved and the microrobot can be actuated with a speed of 5.5 mm s(-1) in 3 degrees of freedom. The novelty of the ultrasonic vibration appears in the output force as well. Contrary to the reduction of friction on the microrobot, the output force increased twice as much by the ultrasonic vibration. Using this high accuracy, high speed, and high power microrobot, swine oocyte manipulations are presented in a microfluidic chip.

Cell micromanipulation with an active handheld micromanipulator

The paper describes the use of an active handheld micromanipulator, known as Micron, for micromanipulation of cells. The device enables users to manipulate objects on the order of tens of microns in size, with the natural ease of use of a fully handheld tool. Micron senses its own position using a purpose-built microscale optical tracker, estimates the erroneous or undesired component of hand motion, and actively corrects it by deflecting its own tool tip using piezoelectric actuators. Benchtop experiments in tip positioning show that active compensation can reduce positioning error by up to 51% compared to unaided performance. Preliminary experiments in bisection of sea urchin embryos exhibit an increased success rate when performed with the help of Micron.

Axon repair: surgical application at a subcellular scale

Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.

Towards A Fully Automated High-Throughput Phototransfection System

We have designed and implemented a framework for creating a fully automated high-throughput phototransfection system. Integrated image processing, laser target position calculation, and stage movements show a throughput increase of > 23X over the current manual phototransfection method while the potential for even greater throughput improvements (> 110X) is described. A software tool for automated off-line single cell morphological measurements, as well as real-time image segmentation analysis, has also been constructed and shown to be able quantify changes in the cell before and after the process, successfully characterizing them, using metrics such as cell perimeter, area, major and minor axis length, and eccentricity values.

Three-dimensional culture of human embryonic stem cell derived hepatic endoderm and its role in bioartificial liver construction

The liver carries out a range of functions essential for bodily homeostasis. The impairment of liver functions has serious implications and is responsible for high rates of patient morbidity and mortality. Presently, liver transplantation remains the only effective treatment, but donor availability is a major limitation. Therefore, artificial and bioartificial liver devices have been developed to bridge patients to liver transplantation. Existing support devices improve hepatic encephalopathy to a certain extent; however their usage is associated with side effects. The major hindrance in the development of bioartificial liver devices and cellular therapies is the limited availability of human hepatocytes. Moreover, primary hepatocytes are difficult to maintain and lose hepatic identity and function over time even with sophisticated tissue culture media. To overcome this limitation, renewable cell sources are being explored. Human embryonic stem cells are one such cellular resource and have been shown to generate a reliable and reproducible supply of human hepatic endoderm. Therefore, the use of human embryonic stem cell-derived hepatic endoderm in combination with tissue engineering has the potential to pave the way for the development of novel bioartificial liver devices and predictive drug toxicity assays.

A uniaxial bioMEMS device for imaging single cell response during quantitative force-displacement measurements

A microfabricated device has been developed for imaging of a single, adherent cell while quantifying force under an applied displacement. The device works in a fashion similar to that of a displacement-controlled uniaxial tensile machine. The device was calibrated using a tipless atomic force microscope (AFM) cantilever and shows excellent agreement with the calculated spring constant. A step input was applied to a single, adherent fibroblast cell and the viscoelastic response was characterized with a mechanical model. The adherent fibroblast was imaged by use of epifluorescence and phase contrast techniques.

EWOD-driven droplet microfluidic device integrated with optoelectronic tweezers as an automated platform for cellular isolation and analysis

We report the integration of two technologies: droplet microfluidics using electrowetting-on-dielectric (EWOD) and individual particle manipulation using optoelectronic tweezers (OET)-in one microfluidic device. The integrated device successfully demonstrates a sequence involving both EWOD and OET operations. We encountered various challenges during integration of the two different technologies and present how they are addressed. To show the applicability of the device in cellular biology, live HeLa cells are used in the experiments. The unique advantages of EWOD and OET make their integration a significant step towards a powerful tool for many applications, such as single cell studies involving multiplexed environmental stimuli.

MEMS and the microbe

In recent years, relatively simple MEMS fabrications have helped accelerate our knowledge of the microbial cell. Current progress and challenges in the application of lab-on-a-chip devices to the viable microbe are reviewed. Furthermore, the degree to which microbiologists are becoming the engineers and are tailoring microbial cells and protocells as potential components for bioMEMS devices is highlighted. We conclude this is a highly productive time for microbiologists and microengineers to unite their shared interest in the micron scale world.

Numerical design of electrical-mechanical traps

We present a coupled immersed interface method-boundary element method (IIM-BEM) numerical technique that predicts the behaviour of deformable cells under the effect of both hydrodynamic and electrical forces. This technique is applied to the study of a hybrid electrical-mechanical trap for single-cell trapping. We report on the effect of different combinations of electrode positions and mechanical properties of the trap on the maximum loading and unloading Reynolds numbers. We also report on the effect that cells moving with the flow have on cells which have been already trapped in a cavity.