Motion Of Beads Research Articles

Magnetoresistive Detection of Magnetic Beads Flowing at High Speed in Microfluidic Channels

An integrated device including microfluidic channels and incorporated magnetoresistive spin valve sensors has been developed and used to detect single magnetic bead motion at cm/s velocities. The sensitivity of the system is high enough to determine the magnetic orientation, the flowing height and the speed of each particle for velocities between 10-23 mm/s and the counting capability of the device is fully working for this range of velocities and below this limit. Sensor signals (between 3-100 muVp-p) correspond to bead moments at different directions indicating a physical rotation of the beads, and a slow response (seconds) of the bead moment to magnetizing field changes. Subsequent magnetic characterization of the micron-sized beads indicates that they are composed of strongly interacting magnetic nanoparticles.

Blasting Off on an Actin Comet Tail

Blasting Off on an Actin Comet Tail

Design Considerations for a Microfluidic Device to Quantify the Platelet Adhesion to Collagen at Physiological Shear Rates

Accurate assessment of blood platelet function is essential in understanding thrombus formation which plays a central role in cardiovascular disease. Parallel plate flow chambers have been widely used as they allow for platelet adhesion on a collagen surface at physiologically relevant fluid mechanical forces. Standard parallel plate flow chambers typically need several milliliters of blood, which is substantially more than can be obtained from small animals. We designed, fabricated, and assessed the functionality of a microfluidic channel with a width of 500 microm and a height of 50 microm in which a wall shear rate of 1000 s(-1) can be achieved with a flow rate of 15 microL/min. The velocity distribution in the microchannel predicted from the equations of motion was compared to experimentally measured velocities of fluorescent beads. This analysis showed that the motion of beads was quite similar to the predicted motion. Adhesion of platelets from whole blood at a shear rate of 1000 s(-1) onto a collagen surface using the microfluidic flow channel was qualitatively similar to platelet adhesion observed with a standard sized parallel plate flow chamber. After 5 min flow the surface coverage of platelets in the microfluidic device was about 55% while in a traditional size flow chamber the surface coverage was about 75%. This suggests that the microfluidic flow chamber can be used to quantify platelet adhesion for system where only very small amounts of blood are available.

Magnetic ratchet for biotechnological applications

Transport and separation of magnetic beads are important in “lab on a chip” environments for biotechnological applications. One possible solution for this is the on-off ratchet concept. An asymmetric magnetic potential and Brownian motion of magnetic beads are required for such a ratchet. The asymmetric magnetic potential is achieved by combining an external magnetic field with a spatially periodic array of conducting lines. In this work finite element method simulations are carried out to design this asymmetric potential and to evaluate transport rates. Furthermore, experiments are carried out so as to compare to the simulation results.

Intracellular Transport: How Do Motors Work Together?

How many motors move cargos on microtubules inside a cell, and how do they work together to achieve regulated transport? A new study uses an optical trap to investigate the motion of protein-bound beads on the surface of flagella to address these questions and comes up with some intriguing answers.

Translocation of magnetic beads using patterned magnetic pathways for biosensing applications

We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9×4×0.1 μm3) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead® M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the sensor surface and as well as drive off the nonspecific binding biomolecules from the surface in performing number of sequential bead detection experiments for future integrated lab-on-a-chip systems.

On a path integral description of the dynamics of an inextensible chain and its connection to constrained stochastic dynamics

The dynamics of a freely jointed chain in the continuous limit is described by a field theory which closely resembles the nonlinear sigma model. The generating functional Ψ[J] of this field theory contains nonholonomic constraints, which are imposed by inserting in the path integral expressing Ψ[J] a suitable product of delta functions. The same procedure is commonly applied in statistical mechanics in order to enforce topological conditions on a system of linked polymers. The disadvantage of this method is that the contact with the stochastic process governing the diffusion of the chain is apparently lost. The main goal of this work is to re-establish this contact. For this purpose, it is shown here that the generating functional Ψ[J] coincides with the generating functional of the correlation functions of the solutions of a constrained Langevin equation. In the discrete case, this Langevin equation describes as expected the Brownian motion of beads connected together by links of fixed length.

A giant liposome for single-molecule observation of conformational changes in membrane proteins

We present an experimental system that allows visualization of conformational changes in membrane proteins at the single-molecule level. The target membrane protein is reconstituted in a giant liposome for independent control of the aqueous environments on the two sides of the membrane. For direct observation of conformational changes, an extra-liposomal site(s) of the target protein is bound to a glass surface, and a probe that is easily visible under a microscope, such as a micron-sized plastic bead, is attached to another site on the intra-liposomal side. A conformational change, or an angular motion in the tiny protein molecule, would manifest as a visible motion of the probe. The attachment of the protein on the glass surface also immobilizes the liposome, greatly facilitating its manipulation such as the probe injection. As a model system, we reconstituted ATP synthase (FOF1) in liposomes tens of μm in size, attached the protein specifically to a glass surface, and demonstrated its ATP-driven rotation in the membrane through the motion of a submicron bead.

ＤＥＭによる媒体撹拌ミル撹拌ロータのピン形状が媒体運動に及ぼす影響の解析

Beads motion in a stirred mill filled with a slurry was simulated by the Discrete Element Method (DEM), enabling to calculate the impact energy of beads. Since the specific impact energy of beads is known to be well correlated with the grinding rate constant, it was monitored as an effective index of grinding performance in the simulation work. The present work is to investigate effect of the pin configuration, particularly, the number of pins attached on the agitator and their length on the beads motion as well as the impact energy. The pins were attached on the axis of the agitator equi-interval in the circumference direction and 3-line in the horizontal axis in the mill. We have found that the beads motion is dependent on the number of pins, and the specific impact energy reaches the maximum value at 8 in number of pins under the present condition. In addition, the maximum value under the specific impact energy is shifted towards large number of pins as the beads filling ratio increases. The specific impact energy of beads is increased with an increase in pin length.

Micromachined Linear Brownian Motor: Transportation of Nanobeads by Brownian Motion Using Three-Phase Dielectrophoretic Ratchet

Nanosystems operating in liquid media may suffer from random Brownian motion due to thermal fluctuations. Biomolecular motors exploit these random fluctuations to generate a controllable directed movement. Inspired by nature, we proposed and realized a nano-system based on Brownian motion of nanobeads for linear transport in microfluidic channels. The channels limit the degree-of-freedom of the random motion of beads into one dimension, which was rectified by a three-phase dielectrophoretic ratchet biasing the spatial probability distribution of the nanobead towards the transportation direction. We micromachined the proposed device and experimentally traced the rectified motion of nanobeads and observed the shift in the bead distribution as a function of applied voltage. We identified three regions of operation; (1) a random motion region, (2) a Brownian motor region, and (3) a pure electric actuation region. Transportation in the Brownian motor region required less applied voltage compared to the pure electric transport.

Veering the motion of a magnetic chemical locomotive in a liquid

The motion of micron-sized catalytic polymer beads coated with thin film or nanoparticle form of Ni in aqueous H(2)O(2) is reported herein. In the absence of any magnetic field, the beads moved vertically upward in the medium, owing to sufficient bubbles deposited on them following catalytic decomposition of H(2)O(2) by Ni. However, in the presence of an external magnetic field (perpendicular to the direction of motion), angular deviation in the motion is observed, with the deviations increasing with the strength of the field. The results are explained based on a model involving interaction of the beads with the external magnetic field.

Citations

Citations

Spectrin Folding versus Unfolding Reactions and RBC Membrane Stiffness

Spectrin (Sp), a key component of the erythrocyte membrane, is routinely stretched to near its fully folded contour length during cell deformations. Such dynamic loading may induce domain unfolding as suggested by recent experiments. Herein we develop a model to describe the folding/unfolding of spectrin during equilibrium or nonequilibrium extensions. In both cases, our model indicates that there exists a critical extension beyond which unfolding occurs. We further deploy this model, together with a three-dimensional model of the junctional complex in the erythrocyte membrane, to explore the effect of Sp unfolding on the membrane's mechanical properties, and on the thermal fluctuation of membrane-attached beads. At large deformations our results show a distinctive strain-induced unstiffening behavior, manifested in the slow decrease of the shear modulus, and accompanied by an increase in bead fluctuation. Bead fluctuation is also found to be influenced by mode switching, a phenomenon predicted by our three-dimensional model. The amount of stiffness reduction, however, is modest compared with that reported in experiments. A possible explanation for the discrepancy is the occurrence of spectrin head-to-head disassociation which is also included within our modeling framework and used to analyze bead motion as observed via experiment.

Fast Drug Release Using Rotational Motion of Magnetic Gel Beads

Accelerated drug release has been achieved by means of the fast rotation of magnetic gel beads. The magnetic gel bead consists of sodium alginate crosslinked by calcium chlorides, which contains barium ferrite of ferrimagnetic particles, and ketoprofen as a drug. The bead underwent rotational motion in response to rotational magnetic fields. In the case of bead without rotation, the amount of drug release into a phosphate buffer solution obeyed non-Fickian diffusion. The spontaneous drug release reached a saturation value of 0.90 mg at 25 minutes, which corresponds to 92% of the perfect release. The drug release was accelerated with increasing the rotation speed. The shortest time achieving the perfect release was approximately 3 minutes, which corresponds to 1/8 of the case without rotation. Simultaneous with the fast release, the bead collapsed probably due to the strong water flow surrounding the bead. The beads with high elasticity were hard to collapse and the fast release was not observed. Hence, the fast release of ketoprofen is triggered by the collapse of beads. Photographs of the collapse of beads, time profiles of the drug release, and a pulsatile release modulated by magnetic fields were presented.

Performance Assessment and Improvement of a Spilt-and-Recombine Micromixer for Immunomagnetic Cell Sorting

Performance of a split-and-recombine micromixer (Tan et al., 2005) is assessed by means of numerical simulation. The micromixer is designed for micro cell sorting systems using immunomagnetic beads, of which working principle is lamination of fluid layers. The fluid motion in a complex three-dimensional geometry is simulated by using the finite difference method and the motion of beads is dealt with the one-way coupling Lagrangian particle tracking method. Although the thickness of laminated layers should ideally reduce by the factor of 2 n (where n is the number of unit-mixers connected in series), the present simulation with a realistic geometry shows that the thickness does not reduce that much. Relatively large unmixed regions are formed in the central region, which deteriorate the mixing performance. The size of the unmixed regions and the degree of mixing are quantitatively investigated. Based on the observation, an improved mixer arrangement is proposed. While the original arrangement proposed by Tan et al. (2005) was to simply connect identical unit-mixers, the present arrangement is to alternately connect the original unit-mixer and one with the mirrored geometry. With this modified arrangement, the unmixed region is suppressed and better mixing is achieved.

Magnetic nanocarriers: from material design to magnetic manipulation

Magnetic nanocarriers play an increasing role in various biomedical applications such as the separation of magnetically 'tagged' DNA, drug delivery or identification of biological species. Recent developments in nanotechnology allow the fabrication of both artificial nanocarriers and magnetic separation devices which may achieve great performances at an incredibly small-volume sample handling. However, as the sizes of magnetic carriers and separation devices diminish, important theoretical and experimental challenges may occur mainly due to the important variations of the surface-to-volume ratio. Under these circumstances, intrinsic properties of individual carriers and their influence on functionality and performances of the magnetic manipulation have to be investigated with a higher degree of accuracy. In this paper, we present the state-of-the-art techniques for extracting accurate information about individual magnetic entities from magnetic measurements performed on ordered arrays or clusters of magnetic nano-objects of various dimensionalities and geometries. As the mutual magnetic interactions may be responsible for collective effects, both analytical and numerical techniques for evaluating the mutual interactions between magnetic nanoparticles and nanowires are reviewed, special emphasis being put on the dimensionality of their assemblages. As the efficiency of the manipulation and capture of individual magnetic carriers in magnetic confinement devices depend strongly on their size, the theoretical description of the motion of magnetic particles under various conditions of flow and field configurations become very important especially with the transition to the nanoscale regime. The equations of motion of magnetic nanocarriers in continuous-flow microfluidic devices are reviewed and some solutions for superparamagnetic interacting clusters, non-interacting beads and ferromagnetic contiguous or codebar nanowires are presented. The influence of both carrier size and transition toward the nanoscale regime on the trappability of some magnetic nanocarriers is evaluated in terms of finite-length Navier boundary conditions and applied in order to compare the motion of superparamagnetic beads and ferromagnetic nanowires in conventional continuous-flow magnetic confinement devices.

Covalent attachment of actin filaments to Tween 80 coated polystyrene beads for cargo transportation

In this manuscript, a new strategy has been reported for circumscribed covalent attachment of barbed and pointed ends of actin filaments to polystyrene beads. A comparative study of attachment of actin filaments to polystyrene beads was performed by blocking functionally active sites on polystyrene beads with nonionic detergents such as Tween 20, Tween 80 and polyethylene glycol (PEG). Effective blocking of active sites was obtained with Tween 80 at 0.1% concentration. Attachment of single bundle of actin filament to bead was assessed by rotational motion of bead tailed actin in front and lateral view. Velocity of actin filaments attached to different size of beads in in-vitro motility assay was calculated to ascertain their attachments. Velocity of actin attached to 1.0 and 3.0 μm polystyrene beads was reduced to 3.0–4.0 and 0.0–1.0 μm/s, respectively as compared to free actin velocity of 4.0–6.0 μm/s. Single point attachment of actin filaments to different size of beads was assessed by decrease in sliding velocity. Present study provides insight into the actin–myosin based molecular motor systems for drug delivery and biosensors applications.

Simple model of cytoskeletal fluctuations

The spontaneous motion of microbeads bound to the cytoskeleton of living cells is not an ordinary random walk. Unlike Brownian motion, the mean-square displacement undergoes a transition from subdiffusive to superdiffusive behavior with time. This transition is associated with characteristic changes of the turning angle distribution. Recent experimental data demonstrated that force fluctuations measured in an elastic hydrogel matrix beneath the cell correlate with the bead motion [C. Raupach, Phys. Rev. E 76, 011918 (2007)]. These data indicate that the bead trajectory is driven by motor forces originating from the actomyosin network and that cytoskeletal remodeling processes with short- and long-time dynamics are mainly responsible for the non-Brownian behavior. We show that the essential statistical properties of the spontaneous bead motion can be reproduced by a particle diffusing in a potential well with a slowly drifting minimum position. Based on this simple model, which can be solved analytically, we develop a biologically plausible numerical model of a tensed and continuously remodeling actomyosin network that accounts quantitatively for the measured data.

Stress fluctuations and motion of cytoskeletal-bound markers

Cytoskeletal (CSK) dynamics such as remodeling and reorganization can be studied by tracking the spontaneous motion of CSK-bound particles. Particle motion is thought to be driven by local, ATP-dependent intracellular force fluctuations due to polymerization processes and motor proteins, and to be impeded by a viscoelastic, metastable cytoskeletal network. The mechanisms that link particle motion to force fluctuations and the CSK dynamics remain unclear. We report simultaneous measurements of the spontaneous motion of CSK-bound particles and of cellular force fluctuations. Cellular force fluctuations were measured by tracking fluorescent markers embedded in an elastic polyacrylamide hydrogel substrate that served as an extracellular matrix (ECM). The motion of CSK-bound particles and markers embedded in the ECM showed both persistence and superdiffusive behavior. Moreover, the movements of CSK-bound beads were temporally and spatially correlated with force fluctuations in the ECM. The findings suggest that the spontaneous motion of CSK-bound beads is driven not by random, local stress fluctuations within a viscoelastic continuum or cage, but rather by stress fluctuations within a tensed and constantly remodeling CSK network that transmits stresses over considerable distances to the ECM.

Time resolved particle dynamics in granular convection

We present an experimental study of the movement of individual particles in a layer of vertically shaken granular material. High-speed imaging allows us to investigate the motion of beads within one vibration period. This motion consists mainly of vertical jumps, and a global ordered drift. The analysis of the system movement as a whole reveals that the observed bifurcation in the flight time is not adequately described by the Inelastic Bouncing Ball Model. Near the bifurcation point, friction plays an important role, and the branches of the bifurcation do not diverge as the control parameter is increased. By fitting the grains trajectories near the wall it is possible to quantify the effective acceleration acting on them. A comparison of the mass centre flying time and the flying time determined for the grains near the wall exposes the underlying mechanism that causes the downward flow.