A magnetic micro-manipulator for application of three dimensional forces

Magnetic manipulation finds diverse applications in actuation, characterization, and manipulation of micro-and nano-scale samples. This paper presents the design and development of a novel magnetic micro-manipulator for application of three-dimensional forces on a magnetic micro-bead. A simple analytical model is proposed to obtain the forces of interaction between the magnetic micromanipulator and a magnetic micro-bead. Subsequently, guidelines are proposed to perform systematic design and analysis of the micro-manipulator. The designed micro-manipulator is fabricated and evaluated. The manipulator is experimentally demonstrated to possess an electrical bandwidth of about 1 MHz. The ability of the micro-manipulator to apply both in-plane and out-of-plane forces is demonstrated by actuating permanent-magnet micro-beads attached to micro-cantilever beams. The deformations of the micro-cantilevers are also employed to calibrate the dependence of in-plane and out-of-plane forces on the position of the micro-bead relative to the micro-manipulator. The experimentally obtained dependences are found to agree well with theory. (C) 2015 AIP Publishing LLC.

Multifunctional magnetic reduced graphene oxide dendrites: Synthesis, characterization and their applications

In this paper, for the first time, we have reported the novel synthesis of reduced graphene oxide (r-GO) dendrite kind of nanomaterial. The proposed r-GO dendrite possesses multifunctional properties in various fields of sensing and separation. The dendrite was synthesized by chemical reaction in different steps. Initially, the r-GO sheet was conjugated with silane group modified magnetic nanoparticle, resulting in nanoparticle decorated r-GO. The above r-GO sheet was further reacted with a new r-GO sheet, resulting in the formation of r-GO dendrite type of structure. Multifunctional behavior of this r-GO dendrite structure was studied by different methods. First, magnetic properties were studied by vibrating sample magnetometer (VSM) and it was found that dendrite structure shows good magnetic susceptibility (180.2 emu/g). The proposed r-GO dendrite also shows a very good antibacterial behavior for Escherichia coli and excellent electrochemical behavior towards ferrocyanide probe molecule. Along with these, it also acts as a substrate for the synthesis of molecularly imprinted polymer for europium metal ion, a lanthanide. The proposed imprinted sensor shows a very high selectivity and sensitivity for europium metal ion (limit of detection= 0.019 mu g L-1) in aqueous as well as real samples. (C) 2015 Elsevier B.V. All rights reserved.

Fully developed thermal transport in combined pressure and electroosmotically driven flow of nanofluid in a microchannel under the effect of a magnetic field

This paper critically analyzes, for the first time, the effect of nanofluid on thermally fully developed magnetohydrodynamic flows through microchannel, by considering combined effects of externally applied pressure gradient and electroosmosis. The classical boundary condition of uniform wall heat flux is considered, and the effects of viscous dissipation as well as Joule heating have been taken into account. Closed-form analytical expressions for the pertinent velocity and temperature distributions and the Nusselt number variations are obtained, in order to examine the role of nanofluids in influencing the fully developed thermal transport in electroosmotic microflows under the effect of magnetic field. Fundamental considerations are invoked to ascertain the consequences of particle agglomeration on the thermophysical properties of the nanofluid. The present theoretical formalism addresses the details of the interparticle interaction kinetics in tune with the pertinent variations in the effective particulate dimensions, volume fractions of the nanoparticles, as well as the aggregate structure of the particulate system. It is revealed that the inclusion of nanofluid changes the transport characteristics and system irreversibility to a considerable extent and can have significant consequences in the design of electroosmotically actuated microfluidic systems.

Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr1-xYxMnO3 (0.1 <= x <= 0.4)

We report structural, magnetic, and dielectric properties of the perovskite compound Pr1-xYxMnO3 (0.1 <= x <= 0.4) studied using dc magnetization, ac susceptibility, neutron powder diffraction, and dielectric techniques. These compounds crystallize in orthorhombic space group (Pnma) in the temperature range 5-300 K. The Mn-O-Mn bond angle decreases with the Y substitution along with an increase in the Jahn-Teller distortion. The Jahn-Teller distortion for Pr0.9Y0.1MnO3 shows an anomalous change near 50 K, below which it falls sharply. Neutron powder diffraction patterns of all reported compositions at low temperature constitute additional magnetic Bragg peaks that suggest magnetic ordering. Magnetic reflections were indexed in the nuclear lattice with the propagation vector k = (0, 0, 0). Rietveld refinement of powder patterns conform to A type antiferromagnetic ordering where moments are aligned ferromagnetically in a-c plane and coupled nearly antiferromagnetically along b-axis resulting in a net ferromagnetic component along the b-direction. The antiferromagnetic transition temperature was deduced from dc magnetization and ac susceptibility data. The transition temperature decreases by nearly 22 K (from 81 K to 59 K) as yttrium content (x) increases from 0.1 to 0.4. Measurements reveal strong frequency dispersion in dielectric constant and dielectric loss. Activation energy and relaxation time are estimated from the Arrhenius plot. It is further shown that relaxation behaviour is altered with yttrium doping concentration. (C) 2015 AIP Publishing LLC.

Giant actuation in bulk carbon nanotubes under coupled electric and magnetic fields

We report an enhanced actuation in bulk carbon nanotubes (CNTs) under coupled electric and magnetic fields, which is much higher than that evaluated in the presence of individual fields. Coupled electric and magnetic fields induce a directional actuation demonstrating a transformation from polarity independent to dependent actuation behavior of CNTs. Both qualitative and quantitative analyses are performed to understand this transformation in the bulk CNTs. Moreover, actuations along radial and axial directions of CNTs have also demonstrated a similar directional behavior.

Influence of substrate temperature on structure, microstructure and magnetic properties of sputtered Fe-Ga thin films

This paper reports the structure, microstructure and magnetic properties of Fe-Ga thin films deposited using DC magnetron sputtering technique on Si(100) substrate kept at different temperatures. Structural studies employing X-ray diffraction and TEM revealed the presence of only disordered A2 phase in the film. Columnar growth of nanocrystalline grains from the substrate was observed in the film deposited at room temperature. With increase in substrate temperature the grain size as well as surface roughness was found to increase. The magnetization of the films deposited at higher substrate temperatures were Found to saturate at lower magnetic held as compared to the room temperature deposited Film. Coercivity was found to decrease with increasing substrate temperature upto a minimum value of similar to 2 Oe for the film deposited at 450 degrees C and with further increase in substrate temperature it was found to increase. A maximum magnetostriction of 200 mu-strains was also observed for the film deposited at 450 degrees C. (C) 2015 Elsevier B.V. All rights reserved

Influence of initial degree of saturation on swell pressures of compacted Barmer bentonite specimens

Densely compacted bentonite or bentonite-sand mixture has been identified as suitable buffer in deep geological repositories as its exceptionally high swelling capacity enables tight contact between the waste canister and surrounding rock. The degree of saturation of the compacted bentonite buffer can increase upon ingress of groundwater from the surrounding rock mass or decrease from evaporation due to high temperature (50-210 degrees C) derived from the waste canister. Available studies indicate that the influence of initial moisture content or degree of saturation on the swell pressure or swell potential of compacted bentonites is unclear. Some studies suggest that initial degree of saturation has an influence, while others suggest that it does not have bearing on the swell pressure of compacted bentonites. This paper examines the influence of initial degree of saturation in montmorillonite voids (termed,S-r,S-MF) on swell pressure of compacted Barmer bentonite-sand mixtures (dry density range: 1.4-2 Mg/m(3)) from micro-structural considerations. The experimental results bring out that, constant dry density specimens that developed similar number of hydration layers upon wetting developed comparable swell pressures and were unaffected by variations in initial S-r,S-MF values. Comparatively, constant dry density specimens that developed dis-similar number of hydration layers upon wetting established different swell pressures and were responsive to variations in initial S-r,S-MF. (C) 2015 Elsevier Ltd. All rights reserved.

Structural and Magnetic Phase Transformations of Hydroxyapatite-Magnetite Composites under Inert and Ambient Sintering Atmospheres

The present work reports the impact of sintering conditions on the phase stability in hydroxyapatite (HA) magnetite (Fe3O4) bulk composites, which were densified using either pressureless sintering in air or by rapid densification via hot pressing in inert atmosphere. In particular, the phase abundances, structural and magnetic properties of the (1-x)HA-xFe(3)O(4) (x = 5, 10, 20, and 40 wt %) composites were quantified by corroborating results obtained from Rietveld refinement of the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. Post heat treatment phase analysis revealed a major retention of Fe3O4 in argon atmosphere, while it was partially/completely oxidized to hematite (alpha-Fe2O3) in air. Mossbauer results suggest the high-temperature diffusion of Fe3+ into hydroxyapatite lattice, leading to the formation of Fe-doped HA. A preferential occupancy of Fe3+ at the Ca(1) and Ca(2) sites under hot-pressing and conventional sintering conditions, respectively, was observed. The lattice expansion in HA from Rietveld analysis correlated well with the amounts of Fe-doped HA determined from the Mossbauer spectra. Furthermore, hydroxyapatite in the monoliths and composites was delineated to exist in the monoclinic (P2(1)/b) structure as against the widely reported hexagonal (P6(3)/m) crystal lattice. The compositional similarity of iron doping in hydroxyapatite to that of tooth enamel and bone presents HA-Fe3O4 composites as potential orthopedic and dental implant materials.

Size Dependent Magnetic Properties of Nd0.7Ca0.3MnO3 Nanomanganite

Nanoscale materials show different properties compared to bulk materials. Due to the size dependent properties the nanoscale materials have potential applications in industry. In this paper the size dependent magnetic properties of Nd0.7Ca0.3MnO3 nanomanganite have been investigated. Nd0.7Ca0.3MnO3 nanoparticles were prepared by low temperature sol-gel method. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and EDAX techniques were used to understand the structure, grain size and composition. Nanoparticles prepared were of the sizes 15 nm, 19 nm and 25 nm respectively. SQUID magnetometer was used to study the magnetic behavior of the nanoparticles. Field cooled (FC) and zero field cooled (ZFC) magnetization of all the nanosamples with respect to temperature was studied and compared. We have observed drastic changes in magnetic properties of 15 nm particles compared to the other nanoparticles. The `charge order peak' was seen to have disappeared in 15 nm particles while it was present in the other nanoparticles. All the nano particles exhibit superparamagnetism whose blocking temperature decreases as a function of decreasing particle size. The possible reasons for the influence of the particle size on the magnetic properties are discussed.

Graphene oxide-Fe3O4 nanoparticle composite with high transverse proton relaxivity value for magnetic resonance imaging

The potential of graphene oxide-Fe3O4 nanoparticle (GO-Fe3O4) composite as an image contrast enhancing material in magnetic resonance imaging has been investigated. Proton relaxivity values were obtained in three different homogeneous dispersions of GO-Fe3O4 composites synthesized by precipitating Fe3O4 nanoparticles in three different reaction mixtures containing 0.01 g, 0.1 g, and 0.2 g of graphene oxide. A noticeable difference in proton relaxivity values was observed between the three cases. A comprehensive structural and magnetic characterization revealed discrete differences in the extent of reduction of the graphene oxide and spacing between the graphene oxide sheets in the three composites. The GO-Fe3O4 composite framework that contained graphene oxide with least extent of reduction of the carboxyl groups and largest spacing between the graphene oxide sheets provided the optimum structure for yielding a very high transverse proton relaxivity value. It was found that the GO-Fe3O4 composites possessed good biocompatibility with normal cell lines, whereas they exhibited considerable toxicity towards breast cancer cells. (C) 2015 AIP Publishing LLC.

Magnetic field assisted stem cell differentiation - role of substrate magnetization in osteogenesis

Among the multiple modulatory physical cues explored to regulate cellular processes, the potential of magneto-responsive substrates in magnetic field stimulated stem cell differentiation is still unperceived. In this regard, the present work demonstrates how an external magnetic field can be applied to direct stem cell differentiation towards osteogenic commitment. A new culture methodology involving periodic delivery of 100 mT static magnetic field (SMF) in combination with HA-Fe3O4 magnetic substrates possessing a varying degree of substrate magnetization was designed for the study. The results demonstrate that an appropriate combination of weakly ferromagnetic substrates and SMF exposure enhanced cell viability, DNA synthesis and caused an early switchover to osteogenic lineage as supported by Runx2 immunocytochemistry and ALP expression. However, the mRNA expression profile of early osteogenic markers (Runx2, ALP, Col IA) was comparable despite varying substrate magnetic properties (diamagnetic to ferromagnetic). On the contrary, a remarkable upregulation of late bone development markers (OCN and OPN) was explicitly detected on weak and strongly ferromagnetic substrates. Furthermore, SMF induced matrix mineralization with elevated calcium deposition on similar substrates, even in the absence of osteogenic supplements. More specifically, the role of SMF in increasing intracellular calcium levels and in inducing cell cycle arrest at G0/G1 phase was elucidated as the major molecular event triggering osteogenic differentiation. Taken together, the above results demonstrate the competence of magnetic stimuli in combination with magneto-responsive biomaterials as a potential strategy for stem cell based bone tissue engineering.

Structural and magnetic properties of Dy3+ doped Y3Fe5O12 for microwave devices

The Dy3+ doped Y3-xDyxFe5O12 (x=0-3) nanopowders were prepared using microwave hydrothermal route. The structural and morphological studies were analyzed using transmission electron microscope, X-ray diffractometer and field emission scanning electron microscope. The nanopowders were sintered at 900 degrees C/90 min using microwave furnace. Dense ceramics with theoretical density of around 95% was obtained. Ferro magnetic resonance (FMR) spectrum and microwave absorption spectrum of Dy3+ doped YIG were studied, the signal exhibits a resonance character for all Dy3+ variations. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing Dy3+ content. The dielectric and magnetic properties (epsilon', epsilon `', mu' and mu `') of Dy3+ doped YIG were studied over a wide range of frequency (1-50 GHz). With increase of Dy3+ both epsilon' and mu' decreased. The low values of dielectric, magnetic properties and broad distribution of FMR line width of these ceramics are opening the real opportunity to use them for microwave devices above K- band frequency. (C) 2015 Elsevier Ltd. All rights reserved.

Effect of sputtering parameters on the structure, microstructure and magnetic properties of Tb-Fe films

The effect of sputtering parameters such as gas pressure and power on the structure, microstructure and magnetic properties of sputtered Tb-Fe thin films was investigated. X-ray diffraction and transmission electron microscopy studies showed that all the films were amorphous in nature irrespective of the sputtering parameters. A fine island kind of morphology was observed at low sputtering power whereas large clusters were seen at higher sputtering power. While the composition of Tb-Fe films remained constant with increasing sputtering power, the magnetic behaviour was found to change from superparamagnetic to ferromagnetic. On the other hand, the increase in argon gas pressure was found to deplete the iron concentration in Tb-Fe thin films, which in turn reduced the anisotropy and Curie temperature. Annealing of the films at 773 K did not result in any crystallization and the magnetic properties were also found to remain unchanged. (C) 2015 Elsevier B.V. All rights reserved.

Polyvinylidene fluoride based lightweight and corrosion resistant electromagnetic shielding materials

Various NixCo1-x alloys (with x varying from 0-60 wt%, Ni: nickel, Co: cobalt) were prepared by vacuum arc melting and mixed with polyvinylidene fluoride (PVDF) to design lightweight, flexible and corrosion resistant materials that can attenuate electromagnetic radiation. The saturation magnetization scaled with the fraction of Co in the alloy. Two key properties such as high-magnetic permeability and high-electrical conductivity were targeted. While the former was achieved using a Ni-Co alloy, multiwalled carbon nanotubes (CNTs) in the composites accomplished the latter. A unique approach was adopted to prepare the composites wherein PVDF powder along with CNTs and Ni-Co flakes were made into a paste, using a solvent, followed by hot pressing. Interestingly, CNTs facilitated in uniform dispersion of the Ni-Co alloy in PVDF, as manifested from synergistic improvement in the electrical conductivity. A significant improvement in the shielding effectiveness (41 dB, >99.99% attenuation) was achieved with the addition of 50 wt% of Ni40Co60 alloy and 3 wt% CNTs. Intriguingly, due to the unique processing technique adopted here, the flexibility of the composites was retained and more interestingly, the composites were resistant to corrosion as compared to only Ni-Co alloy.

Protamine-carboxymethyl cellulose magnetic nanocapsules for enhanced delivery of anticancer drugs against drug resistant cancers

Multidrug resistance is a major therapeutic challenge faced in the conventional chemotherapy. Nanocarriers are beneficial in the transport of chemotherapeutics by their ability to bypass the P-gp efflux in cancers. Most of the P-gp inhibitors under phase II clinical trial are facing failures and hence there is a need to develop a suitable carrier to address P-gp efflux in cancer therapy. Herein, we prepared novel protamine and carboxymethyl cellulose polyelectrolyte multi-layered nanocapsules modified with Fe3O4 nanoparticles for the delivery of doxorubicin against highly drug resistant HeLa cells. The experimental results revealed that improved cellular uptake, enhanced drug intensity profile with greater percentage of apoptotic cells was attained when doxorubicin loaded magnetic nanocapsules were used in the presence of external magnetic field. Hence, we conclude that this magnetic field assisted nanocapsule system can be used for delivery of chemotherapeutics for potential therapeutic efficacy at minimal dose in multidrug resistant cancers. From the Clinical Editor: Many cancer drugs fail when cancer cells become drug resistant. Indeed, multidrug resistance (MDR) is a major therapeutic challenge. One way that tumor cells attain MDR is by over expression of molecular pumps comprising of P-glycoprotein (P-gp) and multidrug resistant proteins (MRP), which can expel chemotherapeutic drugs out of the cells. In this study, the authors prepared novel protamine and carboxymethyl cellulose polyelectrolyte multi-layered nanocapsules modified with Fe3O4 nanoparticles for the delivery of doxorubicin. The results show that there was better drug delivery and efficacy even against MDR tumor cells. (C) 2015 Elsevier Inc. All rights reserved.