Magnetically Actuated Nanorod Arrays as Biomimetic Cilia

Lab on a Chip, 2011

Magnetic actuated microdevices can be used to achieve several complex functions in microfluidics and microfabricated devices. For example, magnetic mixers and magnetic actuators have been proposed to help handling fluids at a small scale. Here, we present a strategy to create magnetically actuated micropillar arrays. We combined microfabrication techniques and the dispersion of magnetic aggregates embedded inside polymeric matrices to design micrometre scale magnetic features. By creating a magnetic field gradient in the vicinity of the substrate, well-defined forces were applied on these magnetic aggregates which in turn induced a deflection of the micropillars. By dispersing either spherical aggregates or magnetic nanowires into the gels, we can induce synchronized motions of a group of pillars or the movement of isolated pillars under a magnetic field gradient. When combined with microfabrication processes, this versatile tool leads to local as well as global substrate actuations within a range of dimensions that are relevant for microfluidics and biological applications.

Microfluidics and Nanofluidics, 2017

Anisotropic carbonyl iron-PolyDiMethylSiloxane (PDMS) composites were developed and implemented in microfluidic devices to serve as magnetic flux concentrators. These original materials provide technological solutions for heterogeneous integration with PDMS. Besides microfabrication advantages, they offer interesting modular magnetic properties. Applying an external magnetic field during the PDMS reticulation leads to the formation of 1D-agglomerates of magnetic particles, organized in the non-magnetic polymer matrix. This induces an increase of susceptibility as compared to composites with randomly dispersed particles. In this report, we explored the gain in reachable magnetophoretic forces in operating microfluidic devices, from the study of magnetic micro-beads motion injected in the microchannel. We show that even at relatively large distances from the magnetically-functionalized channel wall, the anisotropic composite leads to a factor two increase in the magnetophoretic force. Finally, further investigations based on finite element description suggest that the measured benefit of anisotropic composite polymers does not only rely on the global susceptibility increase but also on the local magnetic field gradients originating from the microstructure.

Journal of Physics D: Applied Physics, 2016

In recent years there have been tremendous advances in the versatility of magnetic shuttle technology using nano/micro-scale magnets for digital magnetophoresis. While the technology has been used for a wide variety of single-cell manipulation tasks such as selection, capture, transport, encapsulation, transfection, or lysing of magnetically labeled and unlabeled cells, it has also expanded to include parallel actuation and study of multiple bio-entities. The use of nano/micro-patterned magnetic structures that enable remote control of the applied forces has greatly facilitated integration of the technology with micro uidics, thereby fostering applications in the biomedical arena. The basic design and fabrication of various scaled magnets for remote manipulation of individual and multiple beads/cells, and their associated energies and forces that underlie the broad functionalities of this approach, are presented. One of the most useful features enabled by such advanced integrated engineering is the capacity to remotely tune the magnetic eld gradient and energy landscape, permitting such multipurpose shuttles to be implemented within lab-on-chip platforms for a wide range of applications at the intersection of cellular biology and biotechnology.

Physical Review E, 2009

In this work we mimic the efficient propulsion mechanism of natural cilia by magnetically actuating thin films in a cyclic but non-reciprocating manner. By simultaneously solving the elasto-dynamic, magnetostatic and fluid mechanics equations, we show that the amount of fluid propelled is proportional to the area swept by the cilia. By using the intricate interplay between film magnetization and applied field we are able to generate a pronounced asymmetry and associated flow. We delineate the functional response of the system in terms of three dimensionless parameters that capture the relative contribution of elastic, inertial, viscous and magnetic forces.

Wiley Interdisciplinary Reviews-Nanomedicine and Nanobiotechnology, 2010

Magnetic materials, such as ferrimagnetic and ferromagnetic nanoparticles and microparticles in the form of ferrofluids, can be advantageously used in microelectro-mechanical systems (MEMS) and bioMEMS applications, as they possess several unique features that provide solutions for major microfluidic challenges. These materials come with a wide range of sizes, tunable magnetic properties and offer a stark magnetic contrast with respect to biological entities. Thus, these magnetic particles are readily and precisely maneuvered in microfluidic and biological environments. The surfaces of these particles offer a relatively large area that can be functionalized with diverse biochemical agents. The useful combination of selective biochemical functionalization and 'action-at-a-distance' that a magnetic field provides makes superparamagnetic particles useful for the application in micro-total analysis systems (µ-TAS). We provide insight into the microfluidic transport of magnetic particles and discuss various MEMS and bioMEMS applications .  2010 John Wiley & Sons, Inc. WIREs Nanomed Nanobiotechnol 2010 2 382-399 T he research and development of micro-electro- mechanical systems (MEMS) and bioMEMS devices, which provide platforms for micro-total analytical systems (µ-TAS), 1 is driven by the need for ever-increasing miniaturization. The controlled transport of fluids and fluid-borne solids in these microfluidic environments is typically enabled through a variety of imposed influences, such as through inertial, viscous, surface tension, electrostatic, magnetic, chemical, or molecular interactions. Magnetic particles offer an enabling method that can overcome the major challenges involved with the design of lab-on-achip devices. Magnetic particle-based microfluidics is advantageous, as these particles can be influenced by 'action-at-a-distance'. This ability to manipulate them from a distance free space on microfluidic platforms to include additional components or enable multiplexed batch processing. The magnetic force that the particles experience is relatively insensitive to the biochemical environment and other physical forces, such as electrostatic, surface

ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, Volume 2, 2011

Magnetic nanoparticle suspensions and their manipulation are becoming an alternative research line and have very important applications in the field of microfluidics such as microscale flow control in microfluidic circuits, actuation of fluids in microscale, and drug delivery mechanisms. In microscale, it is possible and beneficial to use magnetic fields as actuators of such nanofluids, where these fluids could move along a gradient of magnetic field so that a micropump without any moving parts could be generated with this technique. Thus, magnetically actuated nanofluids could have the potential to be used as an alternative micro pumping system. Actuation of ferrofluid plugs with a changing magnetic field has been extensively studied in the literature. However; the flow properties of ferrofluids are sparsely investigated when the ferrofluid itself is forced to continuously flow inside a channel. As an extension of previous studies, this study aims to investigate flows of magnetic nanoparticle based nanofluids by a generated magnetic field and to compare the efficiency of the resulting system. Lauric Acid coated Super Paramagnetic Iron Oxide (SPIO-LA) was used as the ferrofluid sample in the experiments to realise actuation. Significant flow rates up to 61.8μL/s at nominal maximum magnetic field strengths of 300mT were achieved in the experiments. Results suggest that nanofluids with magnetic nanoparticles merit more research efforts in micro pumping. Thus, magnetic actuation could be a significant alternative for more common techniques such as electromechanical, electrokinetic, and piezoelectric actuation.

The 13th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2009), Jeju (Korea), 1 - 5 November, 2009

We demonstrate the selective, label-free manipulation of polymer microparticles, including trapping, focussing and continuous flow deflection, within microfluidic devices using diamagnetic repulsion forces.

The Chemical Record, 2018

Magnetophoresis, the manipulation of trajectory of micro-scale entities using magnetic forces, as employed in microfluidic devices is reviewed at length in this article. Magnetophoresis has recently garnered significant interest due to its simplicity, in terms of implementation, as well as cost-effectiveness while being efficient and biocompatible. Theory associated with magnetophoresis is illustrated in this review along with different sources for creating magnetic field gradient commonly employed in microfluidic devices. Additionally, this article reviews the stateof-the-art of magnetophoresis based microfluidic devices, where positive-and negative-magnetophoresis are utilized for manipulation of micro-scale entities (cells and microparticles), employed for operations such as trapping, focusing, separation, and switching of microparticles and cells. The article concludes with a brief outlook of the field of magnetophoresis.

Scientific Reports, 2023

The control and manipulation of superparamagnetic nanoparticles (SP-MNP) is a significant challenge and has become increasingly important in various fields, especially in biomedical research. Yet, most of applications rely on relatively large nanoparticles, 50 nm or higher, mainly due to the fact that the magnetic control of smaller MNPs is often hampered by the thermally induced Brownian motion. Here we present a magnetic device able to manipulate remotely in microfluidic environment SP-MNPs smaller than 10 nm. The device is based on a specifically tailored configuration of movable permanent magnets. The experiments performed in 500 µm capillary have shown the ability to concentrate the SP-MNPs into regions characterized by different shapes and sizes ranging from 100 to 200 µm. The results are explained by straightforward calculations and comparison between magnetic and thermal energies. We provide then a comprehensive description of the magnetic field intensity and its spatial distribution for the confinement and motion of magnetic nanoparticles for a wide range of sizes. We believe this description could be used to establish accurate and quantitative magnetic protocols not only for biomedical applications, but also for environment, food, security, and other areas. Magnetic nanoparticles (MNP) have found multiple uses across a wide spectrum of biomedical applications 1,2 such as hyperthermia for cancer treatment 3 , remotely controlled drug delivery 4 and others both in-vivo 5,6 and invitro 7-9 environments. In tissue engineering, the magnetic manipulation of cells is used in regenerative medicine 10 for efficient cell loading inside scaffolds for bone tissues regeneration 11 or to induce differentiation of MNP-laden embryonic stem cells 12. Finally, MNP-mediated magnetic reprogramming of cellular function-magnetogenetics-is an emerging field in cell biology 13 and neuroscience 14. MNP-based technologies enable the concentration and the manipulation of various bio-agents (BioA) both in-vivo and in-vitro. This is done by capturing the BioAs on selectively functionalized nanoparticle surfaces and then by guiding remotely the formed conjugates by external magnetic field. The superparamagnetic nanoparticles (SP-MNP) represent the most preferable choice for this kind of applications, due to their low aggregation probability and high magnetisation activated by external magnetic field. Magnetic concentration, manipulation, and separation of BioAs is critically important for biosensing, and other in-vitro applications. The magnetic removal of BioAs from analysed solutions is highly selective, efficient, and often faster than centrifugation or filtration 15. It enables efficient manipulations across microfluidics and enhances the sensors performance by removing the interfering species, increasing the concentration of BioA by orders of magnitude. The magnetic technologies are thus increasingly employed to concentrate and detect cells 16,17 and molecular biomarkers 18,19. Also, the realization of microfluidic devices based on the magnetic actuation of MNPs 20 is expected to circumvent some critical issues in microfluidics, where the mixing and processing of fluids at the nanoscale become increasingly inefficient because of the dominance of capillary and viscous forces 21 .

Lab on a Chip, 2006

Magnetic forces are now being utilised in an amazing variety of microfluidic applications. Magnetohydrodynamic flow has been applied to the pumping of fluids through microchannels. Magnetic materials such as ferrofluids or magnetically doped PDMS have been used as valves. Magnetic microparticles have been employed for mixing of fluid streams. Magnetic particles have also been used as solid supports for bioreactions in microchannels. Trapping and transport of single cells are being investigated and recently, advances have been made towards the detection of magnetic material on-chip. The aim of this review is to introduce and discuss the various developments within the field of magnetism and microfluidics.