Magnetic Tweezer System Research Articles

Automated Manipulation of Microswarms Without Real-Time Image Feedback Using Magnetic Tweezers

Microswarms assembled by microparticles have shown promising prospects in targeted delivery. However, the automated manipulation of microswarms remains a considerable challenge due to the limitations of existing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> imaging technology. In this article, we design a magnetic tweezer system with a large workspace of 100 mm × 100 mm × 30 mm, which can assemble, transport, and disassemble microswarms efficiently. The magnetic tweezers generate rotating magnetic fields in the workspace, enabling magnetized microparticles to roll toward a specific point along spiral trajectories. The assembly process and mechanism of microswarms are analyzed. The developed system can assemble low-density magnetic microparticles to form a stable and compact microswarm at a predetermined position. Actuation of the magnetic tweezers allows precise navigation of the swarm without relying on real-time image feedback. The experimental results show that the flexible microswarm can achieve satisfactory motion performance and transmission efficiency. The microswarm can successfully move on a slope with an inclination angle of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$40^\circ $</tex-math></inline-formula> and navigate analog channels. The overall delivery efficiency can reach 92%.

An In Vitro Model System to Test Mechano-Microbiological Interactions Between Bacteria and Host Cells.

The aim of this chapter is to present an innovative technique to visualize changes of the F-actin cytoskeleton in response to locally applied force. We developed an in vitro system that combines micromanipulation of force by magnetic tweezers with simultaneous live cell fluorescence microscopy. We applied pulling forces to magnetic beads coated with the Neisseria gonorrhoeae Type IV pili in the same order of magnitude than the forces generated by live bacteria. We saw quick and robust F-actin accumulation in individual cells at the sites where pulling forces were applied. Using the magnetic tweezers, we were able to mimic the local response of the F-actin cytoskeleton to bacteria-generated forces. In this chapter, we describe our magnetic tweezers system and show how to control it in order to study cellular responses to force.

Real-Time Teleoperation of Magnetic Force-Driven Microrobots With 3D Haptic Force Feedback for Micro-Navigation and Micro-Transportation

Untethered mobile microrobots controlled by an external magnetic gradient field can be employed as advanced biomedical applications inside the human body such as cell therapy, micromanipulation, and noninvasive surgery. Haptic technology and telecommunication, on the other hand, can extend the potentials of untethered microrobot applications. In those applications, users can communicate with the robot operating system remotely to manipulate microrobots with haptic feedback. Haptic sensations artificially constructed by the wirelessly communicated information can assist human operators to experience forces while controlling the microrobots. The proposed system is composed of a haptic device and a magnetic tweezer system, both of which are integrated through a teleoperation technique based on network communication. Users can control the microrobots remotely and feel the haptic interactions with the remote environment in real-time. The 3D haptic environment is reconstructed dynamically by a model-free haptic rendering algorithm using a 2D planar image input of the microscope. The interaction between microrobots and environmental objects is haptically rendered as 3D objects to achieve spatial haptic operation with obstacle avoidance. Moreover, path generation and path guidance forces provide virtual interaction for human users to manipulate the microrobot by following the near-optimal path in path-following tasks. The potential applications of the presented system are medical remote treatment in different sites, remote drug delivery by avoiding physically penetrating through the skin, remotely-controlled cell manipulations, and biopsy without a biopsy needle.

Investigation of Adhesion of Extracellular Polymeric Substances via Magnetic Tweezers

Extracellular polymeric substances (EPSs) serve essential roles in ocean process. EPS molecules can assemble spontaneously, and the adhesion of EPS is involved in the microbial biofilm formation and marine carbon flux. In this study, we investigated the adhesion of EPS using magnetic tweezers system. Mechanical force (∼ 50 pN) was applied to probe the interactions between EPS molecules. First, we used PEG-modified surface to evaluate the influence of various EPS on microbial biofouling; time-response and force-response were tested. Next, we quantified the adhesion efficiency of EPSs collected from Amphora.sp and Sagittula Stellata. In addition, we measured the alteration of EPS-adhesion under salinity change. The results are expected to contribute to our understanding about the adhesion between homo/heterogeneous EPSs and the impacts of microenvironment changes on EPS assembly in the ocean.

Recurrent venous thromboembolism patients form clots with lower elastic modulus than those formed by patients with non‐recurrent disease

Essentials Venous thromboembolism (VTE) recurrence leads to decreased clot elastic modulus in plasma.Recurrent VTE is not linked to changes in clot structure, fiber radius, or factor XIII activity.Other plasma components may play a role in VTE recurrence.Prospective studies should resolve if clot stiffness can be used as predictor for recurrent VTE. SummaryBackgroundVenous thromboembolism (VTE) is associated with a high risk of recurrent events after withdrawal of anticoagulation.ObjectivesTo determine the difference in plasma clot mechanical properties between patients with recurrent VTE (rVTE) and those with non‐recurrent VTE (nrVTE).MethodsWe previously developed a system for determining clot mechanical properties by use of an in‐house magnetic tweezers system. This system was used to determine the mechanical properties of clots made from plasma of 11 patients with rVTE and 33 with nrVTE. Plasma was mixed with micrometer‐sized beads, and thrombin and calcium were added to induce clotting; the mixture was then placed in small capillary tubes, and clotting was allowed to proceed overnight. Bead displacements upon manipulation with magnetic forces were analyzed to determine clot elastic and viscous moduli. Fibrin clot structure was analyzed with turbidimetry and confocal microscopy. Factor XIII was measured by pentylamine incorporation into fibrin.ResultsClots from rVTE patients showed nearly two‐fold less elastic and less viscous moduli than clots from nrVTE patients, regardless of male sex, unprovoked events, family history of VTE, fibrinogen concentration, or body mass index. No differences were observed in clot structure, fibrinolysis rates, or FXIII levels.ConclusionUsing magnetic tweezers for the first time in patient samples, we found that plasma clots from rVTE patients showed a reduced elastic modulus and a reduced viscous modulus as compared with clots from nrVTE patients. These data indicate a possible role for fibrin clot viscoelastic properties in determining VTE recurrence.

Design, Implementation, and Analysis of a 3-D Magnetic Tweezer System With High Magnetic Field Gradient

This paper presents the design, modeling, and implementation of an innovative, high-power hexapole magnetic tweezer system for 3-D micromanipulations. The designed system has six sharp-tipped magnetic poles that are aligned in an inclined Cartesian coordinate system. The installation platform including yokes was made by a 3-D printer using the magnetized material. The magnetic field was generated through the tips after current was applied to individual electromagnetic coils located on each magnetic pole. The effective working space in the system is larger than other similar designs, so it is available to give a wide range of mobility for a microrobot. Strong magnetic fields of up to 6 mT can be generated in the center of the working space, which provides better performance on microscale robot operations. The numerical magnetic field profile was simulated using COMSOL Multiphysics, and the results were compared with the experimental measurement of a magnetic field in the designed system. We prove that the developed hexapole magnetic tweezer has enough power and controllability to guide microswimmers in Newtonian fluid environments and can follow 3-D trajectories. The system will be optimized further to be implemented into cell penetration research. Finally, the application will be deployed into in vivo based environments.

A Three-Dimensional Magnetic Tweezer System for Intraembryonic Navigation and Measurement

Magnetic micromanipulation has the advantage of untethered control, high precision, and biocompatibility and has recently undergone great advances. The magnetic micromanipulation task to tackle in this paper is to three dimensionally navigate a 5-μm magnetic bead inside a mouse embryo and accurately apply forces to intraembryonic structures to perform mechanical measurements at multiple locations. Existing technologies are not able to achieve these navigation and measurement goals because of poor magnetic force scaling and/or lacking the capability of applying an accurately controlled force. This paper reports a three-dimensional magnetic tweezer system that enables, for the first time, intraembryonic magnetic navigation and force application. A single magnetic bead was introduced into a mouse embryo via robotic microinjection. The magnetic tweezer system accurately controlled the position of the magnetic bead via visually servoed magnetic control. By moving the magnetic bead with known forces inside the embryo, cytoplasm viscosity was measured, which is eight times the viscosity of water. For performing mechanical measurements on the cellular structures inside the mouse embryo, the system should be capable of applying forces up to 120 pN with a resolution of 4 pN. The results revealed that the middle region is significantly more deformable than the side regions of the inner cell mass.

Statistical study of biomechanics of living brain cells during growth and maturation on artificial substrates.

There is increasing evidence that mechanical issues play a vital role in neuron growth and brain development. The importance of this grows as novel devices, whose material properties differ from cells, are increasingly implanted in the body. In this work, we studied the mechanical properties of rat brain cells over time and on different materials by using a high throughput magnetic tweezers system. It was found that the elastic moduli of both neurite and soma in networked neurons increased with growth. However, neurites at DIV4 exhibited a relatively high stiffness, which could be ascribed to the high outgrowth tension. The power-law exponents (viscoelasticity) of both neurites and somas of neurons decreased with culture time. On the other hand, the stiffness of glial cells also increased with maturity. Furthermore, both neurites and glia become softer when cultured on compliant substrates. Especially, the glial cells cultured on a soft substrate obviously showed a less dense and more porous actin and GFAP mesh. In addition, the viscoelasticity of both neurites and glia did not show a significant dependence on the substrates' stiffness.

An In Vitro Model System to Test Mechano-microbiological Interactions Between Bacteria and Host Cells.

The aim of this chapter is to present an innovative technique to visualize changes of the f-actin cytoskeleton in response to locally applied force. We developed an in vitro system that combines micromanipulation of force by magnetic tweezers with simultaneous live cell fluorescence microscopy. We applied pulling forces to magnetic beads coated with the Neisseria gonorrhoeae Type IV pili in the same order of magnitude than the forces generated by live bacteria. We saw quick and robust f-actin accumulation at the sites where pulling forces were applied. Using the magnetic tweezers we were able to mimic the local response of the f-actin cytoskeleton to bacteria-generated forces. In this chapter we describe our magnetic tweezers system and show how to control it in order to study cellular responses to force.

1A1-X05 磁極調整機構を有する3次元磁気テザーシステムの開発

This paper presents design and implementation of a three dimensional magnetic tweezer system for measurement of mechanical and rheological properties of living cells. The developed system consists of a 3D magnetic tweezer (MT) having six magnetic poles, a 3D prove visual measurement system and a control system. To reduce assembling error which causes unnecessary nonlinear error of magnetomotive force estimation, a magnetic pole positioning mechanism was introduced. By exerting a constant static current to each magnetic coil attached to a magnetic pole, effectiveness of the positioning mechanism was experimentally validated with the homogeneity of force amplitude of each pole and agreement of model estimation and measurement result.

Probing DNA helicase kinetics with temperature-controlled magnetic tweezers.

Motor protein functions like adenosine triphosphate (ATP) hydrolysis or translocation along molecular substrates take place at nanometric scales and consequently depend on the amount of available thermal energy. The associated rates can hence be investigated by actively varying the temperature conditions. In this article, a thermally controlled magnetic tweezers (MT) system for single‐molecule experiments at up to 40 °C is presented. Its compact thermostat module yields a precision of 0.1 °C and can in principle be tailored to any other surface‐coupled microscopy technique, such as tethered particle motion (TPM), nanopore‐based sensing of biomolecules, or super‐resolution fluorescence imaging. The instrument is used to examine the temperature dependence of translocation along double‐stranded (ds)DNA by individual copies of the protein complex AddAB, a helicase‐nuclease motor involved in dsDNA break repair. Despite moderately lower mean velocities measured at sub‐saturating ATP concentrations, almost identical estimates of the enzymatic reaction barrier (around 21–24 k B T) are obtained by comparing results from MT and stopped‐flow bulk assays. Single‐molecule rates approach ensemble values at optimized chemical energy conditions near the motor, which can withstand opposing loads of up to 14 piconewtons (pN). Having proven its reliability, the temperature‐controlled MT described herein will eventually represent a routinely applied method within the toolbox for nano‐biotechnology.

Mechanical Stiffness Grades Metastatic Potential in Patient Tumor Cells and in Cancer Cell Lines

Cancer cells are defined by their ability to invade through the basement membrane, a critical step during metastasis. While increased secretion of proteases, which facilitates degradation of the basement membrane, and alterations in the cytoskeletal architecture of cancer cells have been previously studied, the contribution of the mechanical properties of cells in invasion is unclear. Here, we applied a magnetic tweezer system to establish that stiffness of patient tumor cells and cancer cell lines inversely correlates with migration and invasion through three-dimensional basement membranes, a correlation known as a power law. We found that cancer cells with the highest migratory and invasive potential are five times less stiff than cells with the lowest migration and invasion potential. Moreover, decreasing cell stiffness by pharmacologic inhibition of myosin II increases invasiveness, whereas increasing cell stiffness by restoring expression of the metastasis suppressor TβRIII/betaglycan decreases invasiveness. These findings are the first demonstration of the power-law relation between the stiffness and the invasiveness of cancer cells and show that mechanical phenotypes can be used to grade the metastatic potential of cell populations with the potential for single cell grading. The measurement of a mechanical phenotype, taking minutes rather than hours needed for invasion assays, is promising as a quantitative diagnostic method and as a discovery tool for therapeutics. By showing that altering stiffness predictably alters invasiveness, our results indicate that pathways regulating these mechanical phenotypes are novel targets for molecular therapy of cancer.

A possible role for integrin signaling in diffuse axonal injury.

Over the past decade, investigators have attempted to establish the pathophysiological mechanisms by which non-penetrating injuries damage the brain. Several studies have implicated either membrane poration or ion channel dysfunction pursuant to neuronal cell death as the primary mechanism of injury. We hypothesized that traumatic stimulation of integrins may be an important etiological contributor to mild Traumatic Brain Injury. In order to study the effects of forces at the cellular level, we utilized two hierarchical, in vitro systems to mimic traumatic injury to rat cortical neurons: a high velocity stretcher and a magnetic tweezer system. In one system, we controlled focal adhesion formation in neurons cultured on a stretchable substrate loaded with an abrupt, one dimensional strain. With the second system, we used magnetic tweezers to directly simulate the abrupt injury forces endured by a focal adhesion on the neurite. Both systems revealed variations in the rate and nature of neuronal injury as a function of focal adhesion density and direct integrin stimulation without membrane poration. Pharmacological inhibition of calpains did not mitigate the injury yet the inhibition of Rho-kinase immediately after injury reduced axonal injury. These data suggest that integrin-mediated activation of Rho may be a contributor to the diffuse axonal injury reported in mild Traumatic Brain Injury.

Imaginary Magnetic Tweezers for Massively Parallel Surface Adhesion Spectroscopy

A massively parallel magnetic tweezer system has been constructed that utilizes the self-repulsion of colloidal beads from a planar interface via a magnetic dipole image force. Self-repulsion enables the application of a uniform magnetic force to thousands of beads simultaneously, which permits the measurement of unbinding histograms at the lowest loading rates ever tested. The adhesion of 9.8 μm polystyrene beads to a fluorocarbon, PEG, and UV-irradiated PEG surfaces were measured between 10(-3)-10(0) pN/s force loading rates, revealing the presence of both kinetic and quasi-equilibrium unbinding regimes.

Temperature Dependence of DNA Elasticity and Cisplatin Activity Studied with a Temperature-Controlled Magnetic Tweezers System

Temperature Dependence of DNA Elasticity and Cisplatin Activity Studied with a Temperature-Controlled Magnetic Tweezers System