On-chip micro-electromagnets for magnetic-based bio-molecules separation

In this study we present a set of guidelines for the design of current carrying micro-conductors/micro-coils (MCs) for magnetic nanoparticles manipulation in biomedical applications. Precise spatial manipulation requires steep magnetic field gradients and due to the consequences of scaling laws, these gradients should be maximized as the size of the particle reduces. Conventional planar coils have many construction and functional limitations, such as generating only small magnetic field gradients, Joule heating, and limited ability to move particles with high spatial resolution. On the other hand, micro-coils can provide a satisfactory solution to all these problems. The geometrical and structural parameters play significant roles in determining the ability to move guide and transport nanoparticles. Design guidelines were generated from a detailed theoretical treatment and finite element analysis (FEA). The spatial distributions of magnetic fields, field gradients and magnetic forces on particles were simulated using FEA for different geometrical/structural parameters and wire arrangements. An array of wires create a chain of magnetic potential wells that are controllable in terms of magnitude and direction and therefore can be used to control the motion and position of magnetic nano-particles by tuning the current through the array.

In order to improve the detection efficiency and accuracy of microfluidic chip, a magnetic beads preset technology were designed by using double permanent magnets as external magnetic field and the motion characteristics of preset magnetic beads were studied. The control principle of magnetic beads preset technology was introduced in detail, and the control structure was designed. The coupled field characteristics for magnetic beads in microchannels were analyzed, and the motion models of magnetic beads were established based on the magnetic beads preset technology, including capture motion and mixing motion. The relationship between the magnetic field force and the flow velocity for capturing magnetic bead, and the mixing time under the influence of flow field and magnetic field were derived. The magnetic beads preset technology effect was verified by experiments and numerical simulations were developed to analyze the influence of aspect ratio of permanent magnet on magnetic field. The study showed that the accuracy and efficiency of the magnetic bead control in the microchannel could be better realized by the magnetic beads preset technology. The derivation of the magnetic bead motion model can understand the motion characteristics of the magnetic bead more clearly, facilitate accurate control of the magnetic bead, and improve the success rate of the microfluidic detection.

A wide range of metal, magnetic, semiconductor, and polymer nanoparticles with tunable sizes and properties can be synthesized by wet-chemical techniques. Magnetic nanoparticles are particularly attractive because their inherent superparamagnetic properties make them desirable for medical imaging, magnetic field assisted transport, and separations and analyses. With such applications on the horizon, synthetic routes for quickly and reliably rendering magnetic nanoparticle surfaces chemically functional have become an increasingly important focus. This Account describes common synthetic routes for making and functionalizing magnetic nanoparticles and discusses initial applications in magnetic field induced separations. The most widely studied magnetic nanoparticles are iron oxide (Fe2O3 and Fe3O4), cobalt ferrite (CoFe 2O4), iron platinum (FePt), and manganese ferrite (MnFe 2O4), although others have been investigated. Magnetic nanoparticles are typically prepared under either high-temperature organic phase or aqueous conditions, producing particles with surfaces that are stabilized by attached surfactants or associated ions. Although it requires more specialized glassware, high-temperature routes are generally preferred when a high degree of stability and low particle size dispersity is desired. Particles can be further modified with a secondary metal or polymer to create core-shell structures. The outer shells function as protective layers for the inner metal cores and alter the surface chemistry to enable postsynthetic modification of the surfactant chemistry. Efforts by our group as well as others have centered on pathways to yield nanoparticles with surfaces that are both easily functionalized and tunable in terms of the number and variety of attached species. Ligand place-exchange reactions have been shown quite successful for exchanging silanes, acids, thiols, and dopamine ligands onto the surfaces of some magnetic particles. Poly(ethylene oxide)-modified phospholipids can be inserted into nonpolar surface monolayers of as-prepared nanoparticles as a method for modifying the surface chemistry that induces water solubility. In general, reactive termini can subsequently be used to append a range of chemical groups. For example, surfactants with trifluoroethylester or azide termini have been used to attach a range of amine- or alkyne-containing species, respectively. Chemically functionalized magnetic nanoparticles are promising as advanced materials for analytical separations and analysis. Magnetic field flow fractionation leverages the size-dependent magnetic moments to purify and separate the components of a complex mixture of particles. Similarly, magnetic field gradients are useful for manipulating transport and separation in simple microfluidic devices. By either approach, magnet-induced transport of the particles is a simple method in which an attached reagent, catalyst, or bioanalytical tag can be moved between flow streams within a lab on a chip device.

A bioengineering course is offered to senior students in the Mechanical Engineering major as an elective at Penn State Behrend in the first semester of their senior year. On average around 20 students enroll in this project-based course and 72% of their grade depends on three comprehensive group projects, one of which is to design a bone plate for a fractured femur. 6% of the grade comes from an individual application presentation, discussing different circumstances in which the concepts in mechanical engineering can be applied to solve/analyze biomedical problems. Background of physiology is introduced in the class while the majority of applicable engineering knowledge was learned in prerequisite courses, such as statics, dynamics, strength of materials, system dynamics, etc. Finite Element Analysis (FEA), an elective offered in both semesters of senior year, is not a prerequisite for this bioengineering course. Most of students enrolled in our bioengineering course either do not have FEA course or are taking FEA concurrently. Therefore in spite of its popularity in the areas related to biomechanics, thus far FEA has not been incorporated in this bioengineering course. Previously, the fractured femur project utilized the applicable theoretical analyses including those from statics, strength of materials, materials, and machine design. In Fall 2015, the instructor of bioengineering course made an effort to have an FEA study on femur and ensuing presentation be completed by a willing student. This student was taking FEA simultaneously with bioengineering, and was scheduled to present during the last week of semester. The instructor of FEA wrote an introductory manual of FEA procedures to analyze a healthy femur using a CAD model of the femur. Then the student used the manual to initiate the FEA study of the fractured femur. A major challenge to the student was the complicated loading and assembly feature of the bone plus the addition of bone plate. After a several week struggle and independent learning, while guided by the faculty members of bioengineering and FEA, the student was able to accomplish the FEA analysis and presented the results to the class. The discrepancy between FEA results and theoretical analysis was shown to be less than 5% in most results. The presentation also included FEA results for a diverse realistic loading and boundary conditions. Since all students had finished the fractured femur project, they actively participated in a meaningful discussion after the presentation. The completion of this project demonstrated the feasibility and importance of incorporating FEA in our bioengineering course. In addition, the presenting student was able to complete a working manual for the FEA analysis of the fractured femur, which can be passed to the future students of this course. A plan is to include FEA in the project as a bonus activity, and regarding the formation of project teams, the instructor would appoint a member who is enrolled in the FEA course. An assignment or project, based on the present FEA study of the femur, can also be incorporated in the FEA course offered at our campus.

Generating ultrasound remotely by means of magnetic fields is an important technological development to circumvent the drawbacks of the traditional means of ultrasound generation techniques. In this report, it is demonstrated that ultrasound is generated from colloidal superparamagnetic nanoparticles when exposed to pulsed and alternating magnetic fields. Comparison of the inhomogeneous and homogeneous magnetic fields indicates that both homogeneous and inhomogeneous magnetic fields could be important for efficient ultrasound generation; however, the latter is more important for dilute colloidal dispersion of magnetic nanoparticles. In strong magnetic fields, the ultrasound generated from the colloidal magnetic nanoparticles shows reasonable agreement with the magnetostriction effect commonly observed for bulk ferromagnetic materials. At low magnetic fields, the colloidal magnetic nanoparticle dispersion produces considerable amount of ultrasound when exposed to ac magnetic fields in the 20–5000 kHz frequ...

Objectives. To establish expected emergent (unexpected) properties of magnetic materials when obtained in aqueous micellar solutions of surfactants (aqueous quantum materials), and their use in fine technologies.Methods. Chemical synthesis of magnetic nanoparticles in aqueous micellar solutions of surfactants of various nature. Characterization of magnetic solutions and nanoparticles by magnetic measurements, spectroscopy, diffractometry, small-angle X-ray diffraction, scanning probe microscopy, and others.Results. The term “water quantum material” refers to materials (micellar solutions) whose properties are mainly determined by the nuclear quantum effect on macroscopic scales (emergent property). Micellar solutions exhibit phenomena and functionality not always consistent with the classical theory of micellization. The article presents in detail the experimental results that suggest the manifestation of the emergent properties of magnetic materials obtained in aqueous micellar solutions of surfactants. In particular, Gd3+ ions in an aqueous micellar solution of sodium dodecyl sulfate exhibit paramagnetic properties, possibly indicating their random arrangement in solution contrary to the classical theory of micellization with an ordered adsorption layer on micelles. Hybrid Pt–Gd nanoparticles are formed in a quantum material with cetylpyridinium chloride as a matrix, although Gd3+ ions must be repelled by CP+ ions on micelles. Nanosized powders of cobalt ferrite and nickel ferrite obtained in a micellar solution of sodium dodecyl sulfate have superparamagnetic properties, although the presence of their precursor ions in the adsorption layer in classical micelles should lead to ferromagnetic properties.Conclusions. The synthesis of nanoparticles in a quantum material opens up the possibility of reducing ions of different signs in one stage during the processing of metallurgy waste, in order to obtain nanoparticles of various metals and their composites. Magnetic nanoparticles obtained in a quantum surfactant material self-assemble on various substrates, enabling the creation of materials whose residual magnetization and coercive field can be controlled at room temperatures.

Thermal efficiency of a ferrofluid-based flat-plate solar collector under the effect of non-uniform magnetic field

This paper deals with theoretical analysis and design of permanent magnet (PM) synchronous motors (PMSMs) with minimized cogging force. Recently, many optimal designs for the PMSMs have been done by finite element (FE) analysis, but such analysis generally is time consuming. In this study, the equation of magnetic flux lines existing between PMs and iron cores is expressed geometrically and the cogging force is calculated theoretically without FE analysis. The form of equation is assumed to be the second-order polynomial and the virtual core is used to express the cogging force in analytical model. The cogging force can be calculated by applying the solved flux line equation and the flux density equation to the Lorentz force equation by using the Maxwell stress tensor. The theoretical analysis of minimized cogging force is applied to several prototypes such as synchronous PM planar motor (SPMPM), 2-DOF PMSM with screw motion, and axial flux PM (AFPM) brushless dc motor in this paper, and the analytical results are validated by FE analyses and experiments.

This study numerically explores the combined effects of flow modulation and Joule heating inside a hexagonal enclosure composed of seawater influenced by an external magnetic field. The cold upper wall of the cavity moves horizontally at a uniform speed, while a rotating thermally conductive circular cylinder is introduced as a flow modulation device to facilitate local vortices' formation. The numerical procedure is conducted utilizing the Galerkin finite element method to resolve the governing equations for both flow and thermal fields. The mixed convection phenomenon is modeled through the Richardson number (0.1 ≤ Ri ≤ 10), whereas the cylinder's rotation is devised by a variable speed ratio (−3 ≤ Ω ≤ 3). The effect of the magnetic field on the system's hydrodynamics is examined via the analysis of various Hartmann numbers (50 ≤ Ha ≤ 100) and Joule heating parameters (J). The model characteristics have been evaluated for streamlines and isotherms, Nusselt numbers, and average temperature. Outcomes demonstrate that the simultaneous influence of the rotating cylinder and the moving top wall dictates the hydrodynamics of the system, achieving up to 137% thermal enhancement. The system's heat transfer is enhanced by buoyancy force, although this effect diminishes with stronger magnetic fields, which stabilize the fluid flow while reducing thermal efficacy. The performance of the rotating flow modulator is the most effective in the forced convection region (0.1 ≤ Ri ≤ 0.4) under a moderately strong magnetic field (Ha = 70). This study presents a novel analysis of a thermo-electromagnetic system in a hexagonal seawater-filled enclosure, integrating rotating flow modulation, external magnetic field, and internal Joule heating. The findings derived from this work can be instrumental in designing marine cooling systems requiring effective heat transfer and flow stabilization.

We show that graphene in a magnetic field possesses by far the highest third-order optical nonlinearity among all known materials. The giant nonlinearity originates from unique electronic properties and selection rules for transitions between Landau levels near the Dirac point. As a result, even one monolayer of graphene gives rise to appreciable nonlinear frequency conversion efficiency for incident infrared radiation. We present quantum-mechanical density-matrix formalism for calculating the nonlinear optical response of graphene in the magnetic field, valid for arbitrarily strong magnetic and optical fields.

This paper studies the non-uniform air-gap caused by stator and rotor deformations, together with its effects on the spatial and temporal spectrum of the radial magnetic force density in an interior permanent magnet synchronous motor (IPMSM). According to the mathematical model of the deformed air-gap length, the superposition method is adopted to derive the air-gap permeance. Then, the formulas of the magnetic flux field and radial force density of the IPMSM considering air-gap deformation are obtained. Considering the stator oval deformation and the rotor centrifugal distortion in the electromagnetic finite element models (FEMs), the finite element analysis (FEA) and experiments of the investigated IPMSM are carried out to verify the results obtained by the theoretical analysis at different operations. Finally, the mathematical correlation between air-gap deformation and electromagnetic vibration is obtained. The result is helpful in solving problems of mutual influence between electromagnetic and mechanical characteristics during the optimization design of IPMSM.

To propose an alternative method of thermoacoustic wave generation based on heating of magnetic nanoparticles (MNPs) using alternating magnetic field (AMF). The feasibility of thermoacoustic wave generation from MNPs by applying a short-burst of AMF or a frequency-modulated AMF is theoretically analyzed. As the relaxation of MNPs is strongly dependent upon the amplitude and frequency of AMF, either an amplitude modulated, fixed frequency AMF (termed time-domain AMF) or a frequency modulated, constant amplitude AMF (termed frequency-domain AMF) will result in time-varying heat dissipation from MNPs, which has the potential to generate thermoacoustic waves. Following Rosensweig's model of specific power loss of MNPs in a steady-state AMF, the time-resolved heat dissipations of MNPs of superparamagnetic size when exposed to a short bursting of AMF and∕or to a linearly frequency chirped AMF are derived, and the resulted acoustic propagation is presented. Based on experimentally measured temperature-rise characteristics of a superparamagnetic iron-oxide nanoparticle (SPION) matrix in a steady-state AMF of various frequencies, the heat dissipations of the SPION under time-domain and frequency-domain AMF configurations that could have practical utility for thermoacoustic wave generation are estimated. The initial rates of the temperature-rise of the SPION matrix were measured at an iron-weight concentration of 0.8 mg∕ml and an AMF frequency of 88.8 kHz to 1.105 MHz. The measured initial rates of temperature-rise were modeled by Rosensweig's theory, and projected to 10 MHz AMF frequency, at which a 1 μs bursting corresponding to a 1.55 mm axial resolution of acoustic detection could contain 10 complete cycles of AMF oscillation and the power dissipation is approximately 84 times of that at 1 MHz. Exposing the SPION matrix to a 1 μs bursting of AMF at 10 MHz frequency and 100 Oe field intensity would produce a volumetric heat dissipation of 7.7 μJ∕cm(3) over the microsecond duration of the AMF burst. If the SPION matrix is exposed to a 1 ms long AMF train at 100 Oe field intensity that chirps linearly from 1 to 10 MHz, the volumetric heat dissipation produced over each 2π phase change of the AMF oscillation is estimated to increase from 0.15 to 1.1 μJ∕cm(3) within the millisecond duration of the chirping of AMF. The heat dissipations upon SPION (∼1 mg∕ml iron-weight concentration) by a 1 μs bursting of 100 Oe AMF at 10 MHz and a 1 ms train of 100 Oe AMF that chirps linearly from 1 to 10 MHz were estimated to determine the potential of thermal-acoustic wave generation. Although thermoacoustic wave generation from MNPs by time- or frequency-domain AMF applications is predicted, the experimental generation of such a wave remains challenging.

Novel magnetic alginate-chitosan beads were prepared for the controlled delivery of albendazole. The magnetic beads were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and vibrating sample magnetometry (VSM). The swelling behavior and in vitro release of albendazole from the beads has been investigated. The magnetic hydrogel beads had showed unique pH-dependent swelling behaviors and a continuous release of the entrapped albendazole occurred. From the magnetometer measurements data, the magnetic alginate-chitosan beads also had superparamagnetic property as well as fast magnetic response. The magnetic beads may be used as a magnetic drug targeting system for albendazole in the gastrointestinal tract.

Magnetic nanoparticles (MNPs) have been considered as potential therapeutic agent carrier for the magnetic targeted-drug delivery in the fight against cancer. Trajectories of MNPs in the blood vessel determine the capture and retention ratio, and the final effectiveness of the treatment. In the present study, a theoretical model of MNPs trajectory is deduced at first. Then two kinds of magnets are proposed, and their magnetic field distributions are calculated through the finite element method software of ANSYS. Using the model and magnetic field inputs, the MNPs trajectories are determined, and the influences of the MNP diameter (Rp), the blood flow velocity (vf) and magnetic field intensity (H) on the trajectories are clarified finally. It is found that the proposed method combining the theoretical model and numerical simulation is feasible. The closed magnetic circuit with concave-convex poles has better MNPs retention ratio than that of the open magnetic circuit because it has higher H and Grad (H). LargeRp, lowvf, and high H are good to capture the MNPs. Especiallyvfand H are critical parameters for the retention ratio of MNPs, and highvfand low H may let MNPs escape the magnetic field region.

Semiflexible nunchucks are block copolymers, which consist of two long blocks of high bending stiffness jointed together by a short block of low bending stiffness. Semiflexible nunchucks that consist of two DNA nanorods jointed by a short segment of double-stranded (ds) DNA and confined in two dimensions have been used in recent experiments by Fygenson and coworkers as a tool to magnify the bending fluctuations of the linking dsDNA, which in turn are used to deduce the persistence length of dsDNA. In a recent theoretical analysis, we showed that in a semiflexible nunchuck with one end grafted, the fluctuations of the position of the free end that is transverse to the grafting direction exhibit a pronounced bimodality, provided that the bending stiffness of the hinge is not very large. In this article, we theoretically analyse a grafted semiflexible nunchuck with a magnetic bead attached to its free end. We show that a transverse magnetic field induces an asymmetry in the bimodal distribution of the transverse fluctuations of the free end. This asymmetry is very sensitive to interactions with a magnetic field and, in principle, could be used in magnetometry (the measurement of a magnetic field or the magnetic moment of the bead). We also investigate how the response of the bimodal distribution of the transverse fluctuations of the free end to a magnetic field depends on the bending stiffness of the nunchuck hinge. In addition, we analyse the closely related systems of a single filament and two filaments jointed at a kink point with one end grafted and the other end attached to a magnetic bead.