Magnetic actuation of microparticles for mass transfer enhancement

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The motion of magnetic microparticles (250μm diameter) in a circular microfluidic reactor with a diameter of 10 mm under time dependent magnetic field has been studied using CFD code COMSOL. The effect of actuation protocol on the local and average particle velocity has been investigated. The local Sh numbers were obtained as a function of angular particle position in the range of Re numbers between 0.05 and 10 while the particle velocity was changed over two orders of magnitude. Under time dependent magnetic field, the thickness of the boundary layer continuously changes which results in an increased mass transfer towards the particle surface under periodic particle velocity conditions as compared to steady state velocity conditions. A good agreement between numerical and experimental data has been observed

Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid

Dynamic-mode atomic force microscopy (AFM) in liquid remains complicated due to the strong viscous damping of the cantilever resonance. Here we show that a high-quality resonance (Q>20) can be achieved in aqueous solution by attaching a microgram-bead at the end of the nanogram-cantilever. The resulting increase in cantilever mass causes the resonance frequency to drop significantly. However, the force sensitivity --- as expressed via the minimum detectable force gradient --- is hardly affected, because of the enhanced quality factor. Via the enhancement of the quality factor, the attached bead also reduces the relative importance of noise in the deflection detector. It can thus yield an improved signal-to-noise ratio when this detector noise is significant. We describe and analyze these effects for a set-up which includes magnetic actuation of the cantilevers and which can be easily implemented in any AFM system that is compatible with an inverted optical microscope.Comment: The following article has been accepted by Journal of Applied Physics. After it is published, it will be found at http://jap.aip.org

Optimization of magnetic actuation protocol to enhance mass transfer in solid/liquid microfluidic systems

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The dynamic properties of a 250 m magnetic microparticle in a time varying magnetic field have been studied in a PDMS microreactor with a diameter of 13 mm using a dual coupled quadrupolar arrangement of electromagnets. A sinusoidal applied magnetic field has dictated a circular motion of the particles in the microreactor in the frequency range below 0.6 Hz. Different circular motion modes have been observed at higher frequencies of the applied field. The particular symmetric arrangement of the magnets has allowed a non-steady-state motion with variation in velocity between magnetic poles. The motion of magnetic particle has been described in terms of average velocity and mean square deviation from average velocity. The effect of actuation protocol parameters (frequency, magnetic field strength and phase shift) on particle velocity and acceleration has been investigated. The maximum average velocity of 0.016 m/s has been observed under an optimized actuation protocol. The mass transfer rate towards the particle surface is mainly influenced by the average velocity while the effect of acceleration/deceleration of the particle has an order of magnitude less influence

Effect of varying magnetic fields on targeted gene delivery of nucleic acid-based molecules

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The importance of high transfection efficiency has been emphasized in many studies investigating methods to improve gene delivery. Accordingly, non-viral transfection agents are widely used as transfection vectors to condense oligonucleotides, DNA, RNA, siRNA, deliver into the cell, and release the cargo. Polyethyleneimine (PEI) is one of the most popular non-viral transfection agents. However, the challenge between high transfection efficiency and toxicity of the polymers is not totally resolved. The delivery of necessary drugs and genes for patients and their transport under safe conditions require carefully designed and controlled delivery systems and constitute a critical stage of patients’ treatment. Compact systems are considered as the strongest candidate for the preparation and delivery of drugs and genes under leak free and safe conditions because of their low energy consumption, low waste disposal, parallel and fast processing capabilities, removal of human factor, high mixing capabilities, enhanced safety, and low amount of reagents. Motivated by this need in the literature, a platform for gene delivery via magnetic actuation of nanoparticles was developed in this study. The use of PEI-SPION (Super paramagnetic ironoxide nanoparticles) as transfection agents in in vitro studies was investigated with the effect of varying magnetic fields provided by a special magnetic system design, which was used as magnetic actuator offering different magnet's turn speeds and directions in the system. Results obtained from magnetic actuator systems were compared to the experiments without actuation and significant enhancement was observed in the transfection efficacies

Comparison on experimental and numerical results for helical swimmers inside channels

Swimming micro robots are becoming feasible in biomedical applications such as targeted drug delivery, opening clogged arteries and diagnosis owing to recent developments in micro and nano manufacturing technologies. It has been demonstrated at various scales that micro helices with magnetic coating or attached to a magnet can move in fluids with the application of external rotating magnetic fields. The motion of micro swimmers interacting with flow inside channels needs to be well understood especially for medical applications where the motion of micro robots inside arteries and conduits in the body become pertinent. In this work, swimming of helical micro robots with magnetic heads inside tubes is modeled with the resistive force theory (RFT) and validated with experiments conducted in glycerin filled mini glass channels placed in rotational magnetic fields. The time-averaged forward velocities of magnetically driven micro swimmers that are calculated by the RFT model agree very well with experimental results

Rotating magnetic field actuation of a multicilia configuration

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The current paper continues the analysis of a completely novel method of fluid manipulation technology in micro-fluidics systems, inspired by nature, namely by the mechanisms found in ciliates. More information on this subject can be found at http://www.hitech-projects.com/euprojects/artic/. In order to simulate the drag forces acting on an array of artificial cilia, we have developed a computer code that is based on fundamental solutions of Stokes flow in a semi-infinite domain. The actuation mechanism consists of a bi-directional rotating excitation magnetic field. The magnetization induced by the magnetic field was calculated in a separate routine based on the Integral Nonlinear Equations Approach with 1D discretization of wire (cilium). Time averaged x-coordinate mass flow rates are computed for several cilium configurations resulting. The outcome and originality of this paper consist on assessing magnetic actuation as a practical tool for obtaining a consistent one-directional fluid flow.This work has been supported through grant ARTIC FP6-2004-NMP-TI4

Non-newtonian 3D ciliary fluid flow in a semi-infinite domain

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Continuing our previous investigations in ciliary fluid transportation (Isvoranu et al., 2010) our present paper looks into the matter of non-newtonian fluid flow. Naturally, in constant properties fluids (newtonian fluids) ciliary transportation is based on a non-symmetric actuation mechanism meaning different geometrical configuration of the cilium during the active and passive stroke. Artificial cilia can mimick this behaviour through asymmetric magnetic actuation as discused in (Isvoranu et. al., 2008). What happens when fluid properties (eg. viscosity) are not constant throughout a beating cycle? Such situation is expected to be encountered when dealing with biological fluids like saliva, for example. In the case of a shear-thinning fluid, like the above mentioned one, the motion can also become asymetric due to deformation rate dependent viscosity that ultimately leads to different time scales of the forward and backward strokes. In the present paper we are investigating a 3D flow generated by an array of cilia embedded in a non-newtonian fluid whose viscosity is characterized by a power low shear rate dependency. The same magnetic actuation mechanism is considered

Implementation of a simplified method for actuation of ferrofluids

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Magnetic actuation of ferrofluids is an emergent field that will open up new possibilities in various fields of engineering. The quality and topology of the magnetic field that is being utilized in such systems is determinant in terms of flow properties, flow rates and overall efficiency. Determining the optimal magnetic field topology to achieve the desired results, and determining the methods by which these magnetic fields are to be generated are central problems of obtaining the desired flow. A healthy comparison of various magnetic field topologies requires a varied set of examples from the most simplified to most sophisticated. Such comparisons are necessary to have a well grounded starting point. This study focuses on a particular pump design that employs a simplified magnetic field topology to obtain ferrofluid flow. The results of this paper such as flow and pressure difference are intended to form a baseline for future reference.Sabancı University Internal Research Grant, no: IACF09-0064