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The integration mode and release modulation of growth factors inside the scaffolds represent major challenges for inductive tissue regeneration. The integration of the bioaffinity of heparin with growth factors and the biomimicry of electrospun fibrous network to extracellular matrices is expected to efficiently bind and gradually release growth factors. Functional ketone groups were incorporated into poly( dl -lactide) backbone through copolymerization with functional e-caprolactone-based monomers. Heparin molecules were conjugated on the fiber surface up to 112.4 ± 3.2 ng/cm 2 , and recombinant basic fibroblast growth factor (bFGF) was loaded onto heparinized fibers up to 96.3 ± 4.7 ng/mg scaffold. The release profiles of bFGF were modulated by the heparin conjugation densities and the molecular weights of heparin conjugated. Higher release rates were found after incubation bFGF-loaded fibers in cell culture media and with NIH3T3 cells than that in buffer solutions. The gradual release of bFGF stimulated the cell growth and collagen secretion for over 21 d, which were more significant for fibrous mats conjugated with heparin of higher density and molecular weights. It is indicated that a novel strategy to fabricate growth factors-loaded fibrous scaffolds has been developed to manipulate desired signals at effective levels within local tissue microenvironment.

Spin-torque excited ferromagnetic resonance (ST-FMR) performed in nanoscale devices can be used to characterize material properties and optimize spintronic devices for applications. In this paper, micromagnetic simulation is employed to study the FMR property in a nano-ring shaped magnetic tunnel junction. The simulation predictions are confirmed by experiments, revealing that two resonance states (mode-1 and mode-2) with different resonance frequencies are excited by a microwave frequency current or magnetic field. The relatively weak response signal of FMR at the negative field can be attributed to the intrinsic asymmetric structure of magnetic tunnel junctions, which leads to a bias-dependent asymmetric spin transfer torque. Besides, high-order harmonics with two and three times the fundamental frequencies of the mode-1 and mode-2 are also observed.

Laser-induced magnetization switching in GdFe ferrimagnets strongly depends on the pulse duration. To gain insight into the ferrimagnetic switching process, Landau–Lifshitz–Gilbert (LLG) spin dynamic modeling is performed at an atomistic-level with two sub-lattice systems. The switching dynamics triggered by laser pulses can be considered as two stages: Demagnetization stage by the laser pulse heating and re-magnetization at the cooling down stage after the pulse impulsion. By tuning the laser pulse duration, the intensity of demagnetization can be well controlled, by which the subsequent magnetization switching during the cooling process can be obtained. The simulation results indicate that the occurrence of the transient ferromagnetic-like (TFL) state is necessary during the magnetization switching process. Furthermore, the thermal temperature and heating time play an important role for the ferrimagnetic switching. In the overheating region, the random switching behavior appears because the TFL state is uncontrollable.

Synchronization of spin-torque nano-oscillators (STNOs) by magnetic dipolar interactions in a parallel electrical connection (PC) introduces the technological possibility for an enhancement of output signal. In this study, we consider two identical or nonidentical STNOs in serial electrical connection (SC). By using a pendulum-like approximation model, we analytically predict the dipolar coupling strength, critical current and frequency of phase-locking precession. The numerical calculations of those analytical expressions are confirmed by macrospin simulations, revealing that the dipolar coupling strength responsible for the phase-locking in SC case is three times larger than that in the PC case for the two STNOs with the same separation, which results in the enlarged and symmetric phase-locking window of frequency versus current. These results suggest that the SC of multiple STNOs could be more promising for the enhancement of output power.

The ferromagnetic thin-film elements can be prepared to form a ?diamond? remanent state that contains two vortices with opposite circulation and with the same or opposite core polarities. The vortex polarity could influence their normal modes through the magnetostatic interactions between two vortices. In this paper, micromagnetic simulations, combined with Fourier techniques, are employed to study the spin-wave (SW) modes excited in a submicron Permalloy ellipse with a vortex pair configuration. After the application of an inplane Gaussian field pulse, it is found that a series of azimuthal SW modes is excited and the high-order harmonics of SW modes are strongly dependent of the core polarities due to the dynamic magnetic interactions between the two vortices.

Reliable manipulation of magnetic droplets is of immense importance for their applications in spin torque oscillators. Using micromagnetic simulations, we find that the antiphase precession state, which originates in the dynamic dipolar interaction effect, is a favorable stable state for two magnetic droplets nucleated at two identical nano-contacts. A magnetic field pulse can be used to destroy their stability and merge them into a big droplet. The merging process strongly depends on the pulse width as well as the pulse strength.

Magnetic fields generated by current lines are the standard way of switching between resistance (R) states in magnetic random access memories. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current crossing the tunnel barrier. Such current induced magnetization switching (CIMS) or current induced switching (CIS) effects were recently observed in thin magnetic tunnel junctions, and attributed to spin transfer (CIMS) or electromigration of atoms into the insulator (CIS). In this work, electromigration-driven resistance changes (resistive switching) are superimposed with thermally induced pinned layer reversal (magnetic switching), producing a reproducible, three-state memory device. The tunnel junctions under study show a tunnel magnetoresistance of 14% with a RA product of 50 �µ m 2 . The reversible electromigration-driven resistance changes amount to 7–8% of the full resistance change and more than 10 4 R-switching events can be current induced without significant damage to the tunnel junction. Typical critical current densities are of the order of 2 × 10 6 Ac m −2 .

Magnetic skyrmions are topologically protected nanoscale objects, which are promising building blocks for novel magnetic and spintronic devices. Here, we investigate the dynamics of a skyrmion driven by a spin wave in a magnetic nanowire. It is found that (i) the skyrmion is first accelerated and then decelerated exponentially; (ii) it can turn L-corners with both right and left turns; and (iii) it always turns left (right) when the skyrmion number is positive (negative) in the T- and Y-junctions. Our results will be the basis of skyrmionic devices driven by a spin wave., Comment: 10 pages, 7 figures

Recently, reversible resistance (R) changes were observed in thin tunnel junctions (TJ) when a critical electrical current was applied. These changes are called current-induced switching (CIS) and are attributed to electromigration in nanoconstrictions in the insulating barrier. Here, we study the CIS effect on a thin TJ prepared by IBD, displaying a 3.4% R change when a CIS cycle is performed at room temperature. After complete (or half) CIS cycles with adequate maximum currents, we monitored R as a function of time. In both cases a non-monotonic relaxation occurs with two distinct relaxation times, τ 1 ∼ 10 min , τ 2 ∼ 1 0 2 min . First R increases (decreases) rapidly, but then a slow relaxation dominates, reducing (increasing) R. These opposite relaxation processes suggest two independent physical mechanisms acting simultaneously inside the TJ. The physical origin of these effects is discussed.

The effective manipulation of skyrmion motion introduces the technologically relevant possibility of skyrmion-based spintronics. Here we show how a magnetic skyrmion can be captured by a radially spatial gradient of the magnetic field. A theoretical model governed by the Thiele equation is employed to study the skyrmion motion. The analytical predictions are compared to micromagnetic simulations based on the Landau–Lifshitz–Gilbert equation, showing that the dynamic behavior of skyrmions strongly depends on the gradient strength of magnetic fields as well as the radius of the skyrmion and the Gilbert damping factor. Moreover, we find that the skyrmions can also be dragged by a moving magnetic tip.

Strawberry packaging based on four different chitosan–poly(vinylalcohol) blend films with chitosan contents of 0 wt %, 20 wt %, 25 wt %, and 30 wt % was tested. The samples were stored at 18 ± 2 °C and 60% ± 5% relative humidity for six days. Strawberry quality was evaluated during and after storage. Strawberries packaged using these films showed significant differences in weight loss and firmness, decay percentage, titratable acidity, total soluble solids, and ascorbic acid content when compared to non-packaged strawberries. The 25 wt % bilayer film showed the best performance in terms of delaying changes in strawberries. The findings suggest that these 25 wt % chitosan films can used to extend strawberry shelf lives while maintaining quality levels.

Summary In recent years, with the prevalence of smartphones, the number of Android malware shows explosive growth. As malicious apps may steal users' sensitive data and even money from mobile and bank accounts, it is important to detect potential malicious behaviors so as to block them. To achieve this goal, we propose a dynamic behavior inspection and analysis framework for malicious behavior detection. A customized Android system is built to record apps' API calls, permission uses, and some other runtime features. We also develop an automated app behavior inspection platform to install and inspect massive samples so as to collect apps' dynamic behavior records. Then these records are exploited to train a string subsequence kernel–based Support Vector Machine (SVM) model, which can be used to classify benign and malicious behaviors offline. To realize online detection, we further extract apps' runtime features including sensitive permission combination uses, sensitive behavior sequences, and user interactions for behavior classification. The classification results can reach an accuracy of 84.9% in offline phase and 99.0% in online phase. Besides, we verify our scheme for identifying malicious apps, and the results show that 71.8% instances of malware samples are identified by running each app for only 18 minutes.

Manipulating dissipative magnetic droplet is of great interest for both the fundamental and technological reasons due to its potential applications in the high frequency spin-torque nano-oscillators. In this paper, a magnetic droplet pair localized in two identical or non-identical nano-contacts in a magnetic thin film with perpendicular anisotropy can phase-lock into a single resonance state by using an oscillating microwave magnetic field. This resonance state is a little away from the intrinsic precession frequency of the magnetic droplets. We found that the phase-locking frequency range increases with the increase of the microwave field strength. Furthermore, multiple droplets with a random initial phase can also be synchronized by a microwave field.

A major challenge in vascular engineering is the establishment of proper microenvironment to guide the spatial organization, growth, and extracellular matrix (ECM) productions of cells found in blood vessels. In the current study, micropatterned fibrous mats with distinct ridges and grooves of different width were created to load smooth muscle cells (SMCs), which were assembled by stacking on vascular endothelial cell (EC)-loaded flat fibrous mats to mimic the in vivo-like organized structure of blood vessels. SMCs were mainly distributed in the ridges, and aligned fibers in the patterned regions led to the formation of elongated cell bodies, intense actin filaments, and expressions of collagen I and α-smooth muscle actin in a parallel direction with fibers. ECs spread over the flat fibrous mats and expressed collagen IV and laminin with a cobblestone-like feature. A z-stack scanning of fluorescently stained fibrous mats indicated that SMCs effectively infiltrated into fibrous scaffolds at the depth of around 200 μm. Compared with SMCs cultured alone, the coculture with ECs enhanced the proliferation, infiltration, and cytoskeleton elongation of SMCs on patterned fibrous mats. Although the coculture of SMCs made no significant difference in the EC growth, the coculture system on patterned fibrous scaffolds promoted ECM productions of both ECs and SMCs. Thus, this patterned fibrous configuration not only offers a promising technology in the design of tissue engineering scaffolds to construct blood vessels with durable mechanical properties, but also provides a platform for patterned coculture to investigate cell-matrix and cell-cell interactions in highly organized tissues.

Combined methods of first-principles calculations and Landau-Lifshitz-Gilbert (LLG) macrospin simulations are performed to investigate the coherent magnetization switching in the MgO/FePt/Pt(001)-based magnetic tunnel junctions triggered by short pulses of electric field through the control of magnetic anisotropy energy (MAE) electrically. First-principles calculations indicate that the MAE of MgO/FePt/Pt(001) film varies linearly with the change of the electric field, whereas the LLG simulations show that the change in MAE by electric field pulses could induce the in-plane magnetization reversal of the free layer by tuning the pulse parameters. We find that there exist a critical pulse width τmin to switch the in-plane magnetization, and this τmin deceases with the increasing pulse amplitude E0. Besides, the magnetization orientation cannot be switched when the pulse width exceeds a critical value τmax, and τmax increases asymptotically with E0. In addition, there exist some irregular switching areas at short pulse width due to the high precessional frequency under small initial angle. Finally, a successive magnetization switching can be achieved by a series of electric field pulses.

Devices displaying resistive-switching are being researched as possible candidates for non-volatile Random Access Memories. Here we study resistance ( R ) switching of non-magnetic origin on CoFe/AlO x /CoFe tunnel junctions. We observe R -switching to a low state for negative currents (top to bottom lead) only, here associated with electromigration (EM) of ions from the bottom metallic electrode into the insulator. EM in the reverse sense occurs only for positive current. We thus show the existence of asymmetric electromigration between the two electrode/barrier interfaces, likely reflecting their structural differences.

We present a micromagnetic simulation for detection of magnetic labels modulated by an ac magnetic field. As the sensing element, spin valves with synthetic ferrimagnetic (SF) free and pinned layers are optimized. At lower fields, the sensors with SF free layers show linear transfer curves, demonstrating a coherent switching due to the strong antiferromagnetic coupling inside the SF free layers. The sensor offset field can be reduced by tuning the effective thickness of SF free and pinned layers. Magnetic simulation for the detection of 250-nm magnetic labels with this sensor shows a linear giant magnetoresistive signal dependence on the number of particles.

Current induced switching (CIS) was recently observed in thin magnetic tunnel junctions and attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. Here we study the CIS effect in tunnel junctions with a Ta layer deposited just below the insulating barrier. We observe enhanced resistance switching with increasing maximum applied current. Anomalous voltage–current characteristics with negative derivative were observed and this effect is attributed to heating in the tunnel junction. We also observe that, after repeatedly applying large current pulses, the electrical resistance decreases sharply through irreversible steps when ions are displaced into the barrier.

Spin-transfer-induced spin-wave excitations in spin-valve nanopillars with perpendicular polarizers have been investigated by micromagnetic simulations. Two coexistent steady states with in-plane magnetizations are observed at small current. With the increased current, periodic oscillating spin waves with frequency from several to tens of gigahertz can be tuned by current alone. High-order harmonics with odd times of fundamental frequency only are observed in these periodic oscillations. The fundamental frequency decreases with the increased thickness of the free layer. Large current could excite chaotic spin waves

A micromagnetic simulation for the detection of magnetic nanobeads by planar Hall sensors is presented. The calculated dipole field created by the polarized nanobeads shows the strong dependence on the distance from beads to the sense plane. In this simulation, nonuniform dipole field, random configuration of beads, and experimental parameters of device were used. Micromagnetic calculation shows the linear signal response to the bead number. This linear behavior is insensitive to the random distribution of beads, but is sensitive to the bead number, indicating the possible application to quantitative biomolecular recognition.

In a previous study, we isolated 1,119 bp of upstream promoter sequence from Bmlp3, a gene encoding a member of the silkworm 30 K storage protein family, and demonstrated that it was sufficient to direct fat body-specific expression of a reporter gene in a transgenic silkworm, thus highlighting the potential use of this promoter for both functional genomics research and biotechnology applications. To test whether the Bmlp3 promoter can be used to produce recombinant proteins in the fat body of silkworm pupae, we generated a transgenic line of Bombyx mori which harbors a codon-optimized Aspergillus niger phytase gene (phyA) under the control of the Bmlp3 promoter. Here we show that the Bmlp3 promoter drives high levels of phyA expression in the fat body, and that the recombinant phyA protein is highly active (99.05 and 54.80 U/g in fat body extracts and fresh pupa, respectively). We also show that the recombinant phyA has two optimum pH ranges (1.5–2.0 and 5.5–6.0), and two optimum temperatures (55 and 37 °C). The activity of recombinant phyA was lost after high-temperature drying, but treating with boiling water was less harmful, its residual activity was approximately 84 % of the level observed in untreated samples. These results offer an opportunity not only for better utilization of large amounts of silkworm pupae generated during silk production, but also provide a novel method for mass production of low-cost recombinant phytase using transgenic silkworms.

Using first-principles density-functional theory calculations, we systematically investigate the magnetic anisotropy of the multilayer system Cu/(FePt)n/MgO, a promising spintronics structure. Particularly, we have studied the influence of the epitaxial strain, thickness of the ferromagnetic layer, and different interfaces on the magnetic anisotropy energy (MAE) of the system. It is found that the thickness of FePt has slight influence on the MAE, while the increase of the in-plane lattice constant a, or tensile strain, can significantly reduce and even change the sign of the MAE. The calculated density of states shows that the occupation number of the minority spin channel of Fe dx(2)-y(2) orbital decreases with the increase of a, which leads to the reduction of the orbital moment anisotropy of the Fe atom and therefore the decrease of MAE. We also consider the influence of the Cu/FePt and FePt/MgO interfaces on the MAE, and find that both interfaces can reduce the MAE. Especially, the effect of the Cu/FePt interface is more pronounced due to the increased occupation number of the minority spin channel of Fe dz(2) orbital.

Vascularization is one of the capital challenges in the establishment of tissue engineering constructs and recovery of ischemic and wounded tissues. The aim of this study was to assess electrospun fibers with loadings of multiple pDNA to allow a localized delivery for an efficient regeneration of mature blood vessels. To induce sufficient protein expression, a reverse microemulsion process was adopted to load pDNA into calcium phosphate nanoparticles (CP-pDNA), which were electrospun into fibers to achieve a sustained release for 4 weeks. Compared with pDNA-infiltrated fibers, the localized and gradual release of pDNA facilitated cell proliferation, gene transfection, and extracellular matrix secretion and enhanced the generation of blood vessels after subcutaneous implantation. Compared with commonly used pDNA polyplexes with poly(ethyleneimine), CP-pDNA nanoparticles induced significantly lower cytotoxicity and less inflammation reaction after implantation into animals. Fibers with encapsulated nanoparticles containing plasmids encoding vascular endothelial growth factor (pVEGF) and basic fibroblast growth factors (pbFGF) led to significantly higher density of mature blood vessels than those containing individual plasmid. It is suggested that the integration of CP-pDNA nanoparticles with loadings of multiple plasmids into fibrous scaffolds should provide clinical relevance for therapeutic vascularization, getting fully vascularized in engineered tissues and regeneration of blood vessel substitutes.

Equipe 101 : Nanomagnétisme et électronique de spin; International audience; Special spin-transfer-driven magnetic behaviors can take place in a spin valve nanopillar with perpendicular anisotropy due to reduced symmetry of easy axis. Micromagnetic simulation demonstrates a dip in the average magnetization curve, which corresponds to the experimentally observed undulation of dc resistance. The dip is a signature of spin-transfer-driven reversable magnetic process with slightly tilted easy axis in the free layer. This featured magnetization dynamics includes non-uniform magnetization precession and multi-mode propagating spin waves, which are attributed to the competition among tilted magnetic anisotropy, magnetic field, and spin transfer torque. (C) 2013 American Institute of Physics.

In this paper, we performed spin simulations at atomistic level to study the temperature dependent properties of perpendicularly magnetized TbFe thin films. The crystallographically amorphous feature of TbFe ferrimagnetic alloys is modeled by using a lattice system with disordered site occupation of rare earth (RE) and transition metal (TM) spins. The simulated Curie temperature ([Formula: see text]) is consistent well with the mean-field approximation theory. With the increase of Tb concentration, the [Formula: see text] decreases almost linearly, whereas the magnetization compensation temperature ([Formula: see text]) increases gradually until the [Formula: see text] value is reached. The inter-sublattice exchange coupling strength [Formula: see text] between the RE and TM atoms can significantly affect [Formula: see text], but has less impact on [Formula: see text]. With the increase of Tb concentration, the TbFe sample of high [Formula: see text] exhibits a much faster increase in [Formula: see text] than the sample with low [Formula: see text]. Moreover, we have tested the simulation code to model the laser pulse induced ultrafast nonequilibrium spin dynamics. As an example, the femto-second pulse laser induced demagnetization and recovery process is clearly reproduced. These features are in a good agreement with the experiments, indicating that the simulation model can capture the basic physics in describing the high temperature dependent magnetic property as well as the ultrafast spin dynamics.

Experimental results on the current-induced resistance change in low-resistance (10-60 /spl Omega//spl middot//spl mu/m/sup 2/) magnetic tunnel junctions with AlO/sub x/ barriers are presented. The observed current-induced resistance change remains unaltered even when the ferromagnetic electrodes are saturated by an external field of 8.5 kOe and, therefore, is not related to the relative magnetization configuration of both electrodes. The critical switching current increases with decreasing barrier thickness (increasing hot-spot density), as well as with increasing junction area. Repeated switching (4000 pulses) leads to junction resistance decrease by 3%-4% and a decrease of the relative current-induced resistance change of about 20%, indicating an increase of hot spots or pinhole density upon current stressing. Critical current increases as current pulsewidth decreases.

The occurrence of pinholes in thin barrier low-resistance junctions degrades the TMR signal and increases the coupling field between pinned and free layers. The tunnel junction coupling field (Hf), junction resistance and TMR signal dependence on the barrier thickness was studied for various types of barriers (HfOx,HfAlOx,ZrAlOx,AlOx). Micromagnetic simulation was employed to simulate the coupling field versus pinhole density. From the coupling field results, HfOx makes the thinnest continuous barriers, followed by doped HfAlOx and ZrAlOx, and then AlOx. HfAlOx and ZrAlOx offer the best compromise between low resistance (1–5 Ω μm2) and reasonable TMR (12%–14%). Pure HfOx can be made with R×A products of 0.4 Ω μm2 but the TMR does not exceed 5.5%.

Current-induced magnetization switching (CIMS) in low resistance tunnel junctions is reported at critical current densities of 1.9×106 A/cm2 for tunnel junction areas ranging from 2 to 3 μm2, and junction resistances from 6 to 20 Ω μm2. Typical tunnel magnetic resistance values for these junctions range from 15% to 21% (measured in an external magnetic field) and 10% to 14% resistance changes are obtained by CIMS. Micromagnetic simulation indicates that vortex fields and spin transfer effects cannot fully account for the observed current-induced switching. Although able to explain the observed transition from a parallel or antiparallel state to a vortex state, it fails to explain the switch back to the original state, at a comparable but symmetrical critical current density.

Current-induced magnetization switching (CIMS) in low-resistance magnetic tunnel junctions was shown at average critical current densities (Jc=1.33×106 A/cm2). When large vertical currents pass through the junctions, spin-transfer torque, and vortex fields can rotate the magnetization of the free layer from the initial parallel state to a vortex state, resulting in 10.8% CIMS resistance change at zero-bias current, which is about half of the resistance change (22%) induced when switching is created by an external field. A micromagnetic simulation including the spin-transfer torque and the vortex field correctly predicts the critical negative-current-inducing switching from the parallel state into the vortex state, but fails to explain the reverse switching from the vortex state into the parallel state at an approximately symmetric positive critical current. Lead fields were analyzed and found to be not the cause of the observed switching. The very small dependence of the switching currents on an external ...

Spatial arrangement of multiple cell types plays a critical role in maintaining the viability of cells and functionality of tissues. Micropatterning has been used to fabricate scaffolds to modulate cell distribution, growth, and functions for reconstructing the anisotropy in native tissues. In the current study, a glass substrate patterned with an electrically conductive circuit was prepared by lithography as a collector for electrospinning. Densely packed fibers were deposited on the top of silver strips and patterned fibrous mats were obtained with distinct ridge and groove areas. Orthogonal alignment was shown for fibers in the ridge and groove areas, and the pattern feature and fiber alignment were well maintained in the ridge during incubation of cells with patterned fibrous mats. Sequential confocal laser scanning from the top of cell-loaded fibrous mats indicated that a larger number of cells were spread in the ridge than that in the groove areas, and cells penetrated into the fibrous mats in the ridge. Microscopic observation and immunofluorescent staining indicated that cells and collagen deposition appeared to have distinct patterns on the fibrous scaffold and aligned along the directionality of fibers with an elongated morphology. It is concluded that lithography can provide the design flexibility of collectors with micrometer-scale precision patterning, and cells can be confined to precise locations, sizes, and shapes by the use of micropatterned fibrous scaffolds without any adverse effect on the cell viability and function. The results suggest the potential of patterned electrospun fibrous mats to construct complex tissues of well organized multiple cell types and with spatially distributed extracellular matrices.

Micromagnetic simulations are performed to study the mechanism of vortex core reversal in a Permalloy elliptical element that contains two vortices with opposite polarities. A short current pulse is applied in the film plane along the short axis of the ellipse. The trajectories of the two vortex cores move either clockwise or anticlockwise, depending on the core polarization. Their reversal mechanisms of the two cores are the same through a creation-annihilation process of vortex-antivortex pair. By analyzing the partial energies of the sample we find that the core reversal occurs once the maximum local energy density reaches the threshold value (e.g., approximately 3.0 x 10(6) J/m3 for Permalloy). Interestingly, this energy threshold is a universal constant, irrespective of the applied current strength, vortex polarity and the sample size.

Although, electrospun composite fibers have shown promise in enhancing growth, differentiation, and mineralization of osteoblasts in vitro, bone repairing capabilities have not been clarified after in vivo implantation up to now. In situ grown composites (IGC) of hydroxyapatite (HA) and poly(DL-lactide) (PDLLA) were obtained from electrospun fibers grafted with gelatin as the induction sites for HA growth. The presence and location of HA nanoparticles within electrospun fibers were proposed to affect the degradation and repairing process of femoral defects. Subcutaneous implantation of IGC led to around 90% of mass loss and 75% of molecular weight reduction during 16 weeks, which were significantly higher than those after in vitro degradation in buffer solutions. In vitro tests on MC3T3-E1 cells indicated that IGC acted as a better cell support to provide favorable conditions for cell proliferation and to stimulate the osteogenic differentiation as compared with electrospun PDLLA fibers, and blend electrospun fibrous composites. Femoral defects were created for in vivo evaluation of bone repairing, indicating that the entire defect was filled by newly formed bone with compact structure after 16 week implantation of IGC. Histological and SEM observations demonstrated a successful bridging of the critical-sized defect with rapid mineralization, continual remodeling, and abundant vasculature. The in situ grown HA nanoparticles on the surface of electrospun fibers improved the biocompatibility with defect sites, promoted the bone formation within fibrous scaffolds and enhanced the bone remodeling, indicating potentials for bone regeneration and repairing of bone defects. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.

For a perpendicular magnetized free layer, a phase-locking steady-state precession is synchronized with the injected circularly polarized spin current. Responses of the spin-wave dynamics with the injected spin-torque are calculated from the Landau-Lifshitz-Gilbert equation in a rotating coordinate frame. Two dynamical precessional modes are found below an upper frequency limit and can be reversibly tuned by the injected current. It is also noted that the perpendicular magnetization will reverse with a circularly spin-polarized current according to the right-hand rule.

Targeting to antigen-presenting cells and efficient intracellular delivery of pDNA are essential for development of microsphere formulations of DNA vaccine.Biodegradable polymers containing acid-labile segments and galactose grafts were developed to entrap pDNA polyplexes into microspheres, which were proposed to promote transfection efficiency of pDNA.Acid-labile characteristics were approved by the hemolysis capabilities of red blood cells and degradation behaviors of matrix polymers; release of pDNA polyplexes from microspheres was significantly accelerated after incubation in acid buffers. Presence of galactose moieties enhanced cellular uptake of microspheres and increased acid-lability due to hydrophilic grafts on acid-labile segments. There was no apparent cytotoxicity of blank microspheres; cytotoxicity of pDNA polyplexes was significantly decreased after encapsulation into and sustained release from microspheres. High transfection efficiency and a dose-dependent transfection were indicated for pDNA polyplex-loaded acid-labile microspheres when balancing with cytotoxicity.Integration of acid-lability, targeting effect into full biodegradable backbone represents an exciting approach to promote transfection efficiency through modulating release of pDNA polyplexes, targeting to antigen-presenting cells and intracellular delivery of pDNA.

Owing to its small size and high stability, the core of magnetic vortices has been proposed as a possible candidate for binary data storage. We have investigated the energetic aspect of the vortex core reversal in ferromagnetic thin-film elements by means of fully three-dimensional finite-element micromagnetic simulations. The simulations show that the reversal occurs once a well-defined threshold in the exchange energy density is reached. We establish the energetic origin of the core reversal by demonstrating that this threshold corresponds to the energy necessary for the production of a vortex-antivortex pair. The effect of the discretization size on the computed exchange energy of a magnetic singularity is discussed. Such a singularity is required for the core reversal process to unfold.

The effective manipulation of the orientation of a vortex core by spin-polarized currents introduces the technologically relevant possibility of addressing individual nanomagnets within large arrays. The vortex configuration, which minimizes the interactions between elements, in principle, allows for high integration densities. Using micromagnetic simulations, we find however that the polarity and vorticity of neighboring vortices can strongly modify the parameters necessary to trigger the core switch, increasing, for example, the switching currents as compared to an insolated disk. Such variations are attributed to the formation of charges during the vortex dynamics and can be interpreted using an analytical model based on the generalized Thiele equation. This model takes into account the dynamic dipolar interaction between neighboring vortices.

Lanthanum oxide (La2O3) films with good hemocompatibility and antibacterial properties have been fabricated using dual plasma deposition. X-ray photoelec- tron spectroscopy (XPS) shows that La exists in the þ3 oxi- dation state. The band gap of the materials is determined to be 3.6 eV. Activated partial thromboplastin time (APTT) and blood platelet adhesion tests were used to evaluate the blood compatibility. The bacteria, Staphylococcus aureus, were used in plate counting tests to determine the surface antibacterial properties. The APTT is a little longer than those of blood plasma and stainless steel (SS). Furthermore, the numbers of adhered, aggregated, and morphologically changed platelets are reduced compared with those on low- temperature isotropic carbon and SS. The antibacterial plate-counting test indicates that La2O3 has good antibacte- rial activity against S. aureus. These unique hemocompati- bility and antibacterial properties make La2O3 useful in many biomedical applications. 2008 Wiley Periodicals, Inc. J Biomed Mater Res 87A: 1027-1033, 2008

Current Induced Resistance Switching (CIS) was recently observed in thin tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. The CIS effect is here studied in TJs with two thin (20 \AA) non-magnetic (NM) Ta electrodes inserted above and below the insulating barrier. We observe resistance (R) switching for positive applied electrical current (flowing from the bottom to the top lead), characterized by a continuous resistance decrease and associated with current-driven displacement of metallic ions from the bottom electrode into the barrier (thin barrier state). For negative currents, displaced ions return into their initial positions in the electrode and the electrical resistance gradually increases (thick barrier state). We measured the temperature (T) dependence of the electrical resistance of both thin- and thick-barrier states ($R_b$ and R$_B$ respectively). Experiments showed a weaker R(T) variation when the tunnel junction is in the $R_b$ state, associated with a smaller tunnel contribution. By applying large enough electrical currents we induced large irreversible R-decreases in the studied TJs, associated with barrier degradation. We then monitored the evolution of the R(T) dependence for different stages of barrier degradation. In particular, we observed a smooth transition from tunnel- to metallic-dominated transport. The initial degradation-stages are related to irreversible barrier thickness decreases (without the formation of pinholes). Only for later barrier degradation stages do we have the appearance of metallic paths between the two electrodes that, however, do not lead to metallic dominated transport for small enough pinhole radius., Comment: 10 pages, 3 figures

We report on the switching of a magnetic vortex core in a sub-micron Permalloy disk, induced by a short current pulse applied in the film plane. Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque terms are used to investigate the current-driven magnetization dynamics. We predict that a core reversal can be triggered by current bursts a tenth of a nanosecond long. The vortex core reversal process is found to be the same as when an external field pulse is applied. The control of a vortex core's orientation using current pulses introduces the technologically relevant possibility to address individual nanomagnets within dense arrays., 3 pages, 3 figures

Laser-induced magnetization dynamics in Gd[Formula: see text]Fe[Formula: see text]Co[Formula: see text] (GdFeCo) film was investigated by time-resolved magneto-optical effect. After an ultrafast demagnetization and a magnetization recovery process, a second slower drop from several picoseconds (ps) to 200[Formula: see text]ps was observed. Previous report explained it as the demagnetization of Gd sublattice. However, when timescale extended up to 5 nanosecond (ns), we identified it as the part of an oscillated magnetization precession. It presents the change of magnetization orientation rather than the change of magnetization amplitude. Our results reveal that the low thermal diffusion coefficient of GdFeCo film plays an important role in the laser-induced magnetization dynamics of GdFeCo film.

The spin-torque induced magnetization precession dynamics are studied in a spin-valve with a tilted spin polarizer. Macrospin simulations demonstrate that the frequency of precession state depends both on the external DC current and the intrinsic parameters of devices such as the tilted angle of spin polarizer, the damping factor and saturation magnetization of the free layer. The dependence role of those parameters is characterized by phase diagrams. An analytical model is presented, which can successfully interpret the features of precession frequency.

In this paper, spin-dependent multiple reflection effect on spin-transfer torque (STT) has been theoretically and numerically studied in a spin valve nanopillar with a single or dual spin-polarizer. By using a scattering matrix method, we formulate an analytical expression of STT that contains the multiple interfacial reflection effect. It is found that the multiple reflections could enhance the STT efficiency and reduce the critical switching current. The STT efficiency depends on the spin polarization of both the free layer and polarizer. In the nanopillars with a dual spin polarizer, the multiple reflections would cause an asymmetric frequency dependence on the applied current, albeit exactly the same parameters are used in all three ferromagnetic layers, indicating that the frequency in the negative current varies much faster than that in the positive case.

In magnetic nanostructures one usually uses a magnetic field to commute between two resistance (R) states. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current, preferably of low intensity. Such Current Induced Switching (CIS) was recently observed in thin magnetic tunnel junctions, and attributed to electromigration of atoms into/out of the insulator. Here we study the Current Induced Switching, electrical resistance, and magnetoresistance of thin MnIr/CoFe/AlO$_x$/CoFe tunnel junctions. The CIS effect at room temperature amounts to 6.9% R-change between the high and low states and is attributed to nanostructural rearrangements of metallic ions in the electrode/barrier interfaces. After switching to the low R-state some electro-migrated ions return to their initial sites through two different energy channels. A low (high) energy barrier of $\sim$0.13 eV ($\sim$0.85 eV) was estimated. Ionic electromigration then occurs through two microscopic processes associated with different types of ions sites/defects. Measurements under an external magnetic field showed an additional intermediate R-state due to the simultaneous conjugation of the MR (magnetic) and CIS (structural) effects., 6 pages, 4 figures