Spin Chirality Fluctuation and Anomalous Hall Effect in Itinerant Ferromagnets

The anomalous Hall effect due to the spin chirality order and fluctuation is studied theoretically in a Kondo lattice model without the relativistic spin-orbit interaction. Even without the correlations of the localized spins, $\sigma_{xy}$ can emerge depending on the lattice structure and the spin anisotropy. We reveal the condition for this chirality-fluctuation driven mechanism for $\sigma_{xy}$. Our semiquantitative estimates for a pyrochlore oxide Nd$_2$Mo$_2$O$_7$ give a finite \sigma_{xy} \sim 10 \Ohm^{-1} \cm^{-1} together with a high resistivity \rho_{xx} \sim 10^{-4}-10^{-3} \Ohm \cm, in agreement with experiments.Comment: 5 pages, including 4 figure

Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2

Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature (T) dependence of the electronic structure in BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic transformation in Fermi surface (FS) shape across TN is observed, as expected by first-principles band calculations. Polarization-dependent ARPES and band calculations consistently indicate that the observed FSs at kz ~ pi in the low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading to the two-fold electronic structure. These results indicate that magneto-structural transition in BaFe2As2 accompanies orbital-dependent modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter

The osteogenic differentiation of rat bone marrow stromal cells cultured with dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles

There is an increasing interest in developing novel macromolecular vehicles for the intracellular and controlled delivery of bioactive molecules, since they can allow modulation of the cellular functions in a more effective manner ex vivo, and maintain the cellular phenotype in vivo upon re-implantation. The present study was designed to investigate the effect of combining novel dexamethasone-loaded carboxymethylchitosan/ poly(amidoamine) dendrimer (Dex-loaded CMCht/PAMAM) nanoparticles and, both HA and SPCL scaffolds (3D system) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells (RBMSCs) in vitro. A luminescent cell viability assay using RBMSCs was performed for screening cytotoxicity of the developed HA and SPCL scaffolds. Results corroborated previous ones which have demonstrated in vitro, the superior performance of the HA and SPCL scaffolds on supporting cells adhesion and proliferation. Furthermore, this work showed that RBMSCs seeded onto the surface of both HA and SPCL scaffolds differentiate into osteoblasts when cultured in the presence of 0.01 mg ml!1 Dexloaded CMCht/PAMAM dendrimer nanoparticles. In addition, results demonstrated that Dex-loaded CMCht/PAMAM dendrimer nanoparticles combined with the HA enhance osteogenesis by increasing ALP activity and mineralization of the extra-cellular matrix. The pre-incubation of stem cells with these kinds of nanoparticles allows the delivery of Dex inside the cells and directly influences their cellular fate, being a promising new tool to be used in cells and tissue engineering strategies.The authors thank the funds provided by Portuguese Foundation for Science and Technology (FCT) through POCTI and FEDER programmes including project ProteoLight (PTDC/FIS/68517/2006). This work was also carried out with the support of the European Union funded STREP Project HIPPOCRATES (NMP3-CF-2003-505758) and European NOE EXPERTISSUES (NMP3-CT-2004-500283). The funding provided by Canon Foundation in Europe is gratefully acknowledged

Ex vivo culturing of stromal cells with dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles promotes ectopic bone formation

Recently, our group has proposed a combinatorial strategy in tissue engineering principles employing carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles (CMCht/PAMAM) towards the intracellular release and regimented supply of dexamethasone (Dex) aimed at controlling stem cell osteogenic differentiation in the absence of typical osteogenic inducers, in vivo. In this work, we have investigated if the Dex-loaded CMCht/PAMAM dendrimer nanoparticles could play a crucial role in the regulation of osteogenesis, in vivo. Macroporous hydroxyapatite (HA) scaffolds were seeded with rat bone marrow stromal cells (RBMSCs), whose cells were expanded in MEM medium supplemented with 0.01 mg ml−1 Dexloaded CMCht/PAMAM dendrimer nanoparticles and implanted subcutaneously on the back of rats for 2 and 4 weeks. HA porous ceramics without RBMSCs and RBMSCs/HA scaffold constructs seeded with cells expanded in the presence and absence of 10−8 M Dex were used as controls. The effect of initial cell number seeded in the HA scaffolds on the bone-forming ability of the constructs was also investigated. Qualitative and quantitative new bone formation was evaluated in a non-destructive manner using micro-computed tomography analyses of the explants. Haematoxylin and Eosin stained implant sections were also used for the histomorphometrical analysis. Toluidine blue staining was carried out to investigate the synthesis of proteoglycan extracellular matrix. In addition, alkaline phosphatase and osteocalcin levels in the explants were also quanti!ed, since these markers denote osteogenic differentiation. At 4 weeks post-implantation results have shown that the novel Dex-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles may be bene!cial as an intracellular nanocarrier, supplying Dex in a regimented manner and promoting superior ectopic de novo bone formation.This study was supported by the Portuguese Foundation for Science and Technology (FCT) through POCTI and FEDER programmes (SFRH/BD/21786/2005) and by the Canon Foundation in Europe. We wish to thank P.B. Malafaya for the technical support during the micro-CT analyses, and to Materialise for providing the Mimics software. This work was also supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and European NoE EXPERTISSUES (NMP3-CT-2004-500283)

Dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles enhances bone formation in vivo

[Excerpt] Dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles, CMC/PAMAM-Dex were successfully synthesized to find applications as a controlled system of relevant molecules in Bone Tissue Engineering. These are aimed at modulatingtheproliferation anddifferentiationofstem cells,both invitro and in vivo. In previous work, we have demonstrated that CMC/ PAMAM-Dex nanoparticles are internalized with high efficiency by different cell types, namely osteoblastic-cells, SaOs-2 and rat bone marrow stromal cells, RBMSCs. The biocompatibility of HA and SPCL scaffolds was also assessed by means of seeding RBMSCs onto the materials and performing a luminescent cell viability assay, after 24 and 72hrs. [...]info:eu-repo/semantics/publishedVersio

In vivo study of dendron-like nanoparticles for stem cells tune-up : from nano to tissues

The control of stem cell differentiation to obtain osteoblasts in vivo is still regarded as a challenge in stem-cell-based and bone-tissue engineering strategies. Biodegradable dexamethasone-loaded dendron-like nanoparticles (NPs) of carboxymethylchitosan/poly(amidoamine) dendrimer have been proposed as intracellular drug-delivery systems of bioactive molecules. In this study, combination of nanotechnology, stem-cell engineering and tissue engineering is proposed in pre-programming the fate of rat bone marrow stromal cells (RBMSCs) towards osteoblasts cells and development of new bone tissue, in vivo. This work demonstrated that the developed NPs were able to be taken up by RBMSCs, and exhibited a noncytotoxic behavior in vitro. The performance of the developed dendronlike NP system for the intracellular delivery of dexamethasone was investigated by seeding the engineered RBMSCs onto starch-polycaprolactone scaffolds ex vivo, and implanting subcutaneously in the back of Fischer 344/N rats (Syngeneic), in the absence of the typical osteogenic supplements. Favorable results were observed in vivo, thus suggesting that stem cell “tune-up” strategy can open up a new regenerative strategy for bone-tissue engineering.The authors would like to thank the financial support from Portuguese Foundation for Science and Technology (FCT, project SmartCarbo, ref. PTDC/QUI/68804/2006), through POCTI and FEDER programs. The funding provided by Canon Foundation in Europe is gratefully acknowledged. This work was also carried out under the scope of the European NoE EXPERTISSUES (NMP3-CT-2004-500283) and HIPPOCRATES (NMP3-CT-2003-505758) projects

Anomalous Hall Effect and Skyrmion Number in Real- and Momentum-space

We study the anomalous Hall effect (AHE) for the double exchange model with the exchange coupling $|J_H|$ being smaller than the bandwidth $|t|$ for the purpose of clarifying the following unresolved and confusing issues: (i) the effect of the underlying lattice structure, (ii) the relation between AHE and the skyrmion number, (iii) the duality between real and momentum spaces, and (iv) the role of the disorder scatterings; which is more essential, $\sigma_H$ (Hall conductivity) or $\rho_H$ (Hall resistivity)? Starting from a generic expression for $\sigma_H$, we resolve all these issues and classify the regimes in the parameter space of $J_H \tau$ ($\tau$: elastic-scattering time), and $\lambda_{s}$ (length scale of spin texture). There are two distinct mechanisms of AHE; one is characterized by the real-space skyrmion-number, and the other by momentum-space skyrmion-density at the Fermi level, which work in different regimes of the parameter space.Comment: 4 pages, 1 figure, REVTe

Chirality driven anomalous Hall effect in weak coupling regime

Anomalous Hall effect arising from non-trivial spin configuration (chirality) is studied based on the $s$-$d$ model. Considering a weak coupling case, the interaction is treated perturbatively. Scattering by normal impurities is included. Chirality is shown to drive locally Hall current and leads to overall Hall effect if there is a finite uniform chirality. This contribution is independent of the conventional spin-orbit contribution and shows distinct low temperature behavior. In mesoscopic spin glasses, chirality-induced anomalous Hall effect is expected below the spin-glass transition temperature. Measurement of Hall coefficient would be useful in experimentally confirming the chirality ordering

Surface engineered carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles for intracellular targeting

Novel highly branched biodegradable macromolecular systems have been developed by grafting carboxymethylchitosan (CMCht) onto low generation poly(amidoamine) (PAMAM) dendrimers. Such structures organize into sphere-like nanoparticles that are proposed to be used as carriers to deliver bioactive molecules aimed at controlling the behavior of stem cells, namely their proliferation and differentiation. The nanoparticles did not exhibit significant cytotoxicity in the range of concentrations below 1 mg mL"1, and fluorescent probe labeled nanoparticles were found to be internalized with highly efficiency by both human osteoblast-like cells and rat bone marrow stromal cells, under fluorescence-activated cell sorting and fluorescence microscopy analyses. Dexamethasone (Dex) has been incorporated into CMCht/PAMAM dendrimer nanoparticles and release rates were determined by high performance liquid chromatography. Moreover, the biochemical data demonstrates that the Dex-loaded CMCht/PAMAM dendrimer nanoparticles promote the osteogenic differentiation of rat bone marrow stromal cells, in vitro. The nanoparticles exhibit interesting physicochemical and biological properties and have great potential to be used in fundamental cell biology studies as well as in a variety of biomedical applications, including tissue engineering and regenerative medicine