RESUMEN

Local thermal magnetization fluctuations in Li-doped MnTe are found to increase its thermopower α strongly at temperatures up to 900 K. Below the Néel temperature (T N ~ 307 K), MnTe is antiferromagnetic, and magnon drag contributes αmd to the thermopower, which scales as ~T 3. Magnon drag persists into the paramagnetic state up to >3 × T N because of long-lived, short-range antiferromagnet-like fluctuations (paramagnons) shown by neutron spectroscopy to exist in the paramagnetic state. The paramagnon lifetime is longer than the charge carrier-magnon interaction time; its spin-spin spatial correlation length is larger than the free-carrier effective Bohr radius and de Broglie wavelength. Thus, to itinerant carriers, paramagnons look like magnons and give a paramagnon-drag thermopower. This contribution results in an optimally doped material having a thermoelectric figure of merit ZT > 1 at T > ~900 K, the first material with a technologically meaningful thermoelectric energy conversion efficiency from a spin-caloritronic effect.

RESUMEN

The association structures formed by cationic liposomes and DNA (Deoxyribonucleic acid)-liposome have been effectively utilized as gene carriers in transfection assays. In this research study, cationic liposomes were prepared using a modified lipid film hydration method consisting of a lyophilization step for gene delivery applications. The obtained results demonstrated that the mean particle size had no significant change while the polydispersity (PDI) increased after lyophilization. The mean particle size slightly reduced after lyophilization (520±12nm to 464±25nm) while the PDI increased after lyophilization (0.094±0.017 to 0.220±0.004). In addition. The mean particle size of vesicles increases when DNA is incorporated to the liposomes (673±27nm). According to the Scanning Electron Microscopy (SEM) and transmission electron microscopy (TEM) images, the spherical shape of liposomes confirmed their successful preservation and reconstitution from the powder. It was found that liposomal formulation has enhanced transfection considerably compared to the naked DNA as negative control. Finally, liposomal formulation in this research had a better function than Lipofectamine® 2000 as a commercialized product because the cellular activity (cellular protein) was higher in the prepared lipoplex than Lipofectamine® 2000.

Asunto(s)

ADN , Técnicas de Transferencia de Gen , ADN/química , ADN/genética , ADN/farmacología , Células HEK293 , Humanos , Operón Lac , Liposomas

RESUMEN

It has been frequently reported that cell viability on stainless steels is improved by increasing their corrosion resistance. The question that arises is whether human cell viability is always directly related to corrosion resistance in these biostable alloys. In this work, the microstructure and in vitro corrosion behavior of a new class of medical-grade stainless steels were correlated with adult human mesenchymal stem cell viability. The samples were produced by a powder metallurgy route, consisting of mechanical alloying and liquid-phase sintering with a sintering aid of a eutectic Mn-Si alloy at 1050 °C for 30 and 60 min, leading to nanostructures. In accordance with transmission electron microscopic studies, the additive particles for the sintering time of 30 min were not completely melted. Electrochemical impedance spectroscopic experiments suggested the higher corrosion resistance for the sample sintered for 60 min; however, a better cell viability on the surface of the less corrosion-resistant sample was unexpectedly found. This behavior is explained by considering the higher ion release rate of the Mn-Si additive material, as preferred sites to corrosion attack based on scanning electron microscopic observations, which is advantageous to the cells in vitro. In conclusion, cell viability is not always directly related to corrosion resistance in stainless steels. Typically, the introduction of biodegradable and biocompatible phases to biostable alloys, which are conventionally anticipated to be corrosion-resistant, can be advantageous to human cell responses similar to biodegradable metals.

Asunto(s)

Ensayo de Materiales , Células Madre Mesenquimatosas/metabolismo , Acero Inoxidable/farmacología , Adulto , Supervivencia Celular/efectos de los fármacos , Corrosión , Femenino , Humanos , Masculino , Células Madre Mesenquimatosas/citología

RESUMEN

A new composition of gelatin/bioactive-glass/silver nanoparticle was synthesized and employed to prepare antibacterial macroporous scaffolds with potential applications in bone tissue engineering. A set of macroporous nanocomposite scaffolds were developed from an aqueous solution of gelatin by freeze-drying and crosslinking using genipin at ambient temperature. Silver nanoparticles were successfully synthesized in situ in gelatin solution by heat treatment reduction as a simple and "green" method in which gelatin acted as a natural reducing and stabilizing agent. The effect of the incorporation of the bioactive-glass and the silver nanoparticle concentration on the physicochemical properties of the scaffolds, such as the gel fraction, porosity, in vitro enzyme degradation, morphology, and swelling behavior was studied. Furthermore, the in vitro viability of human mesenchymal stem cells (hMSC) and the antibacterial activity against gram-negative Escherichia coli and gram-positive Staphylococcus aureus were tested on the scaffolds. It was found that upon the addition of silver nanoparticles the porosity, pore size, swelling, and antibacterial properties were enhanced. The silver nanoparticles increased the in vitro enzyme degradation in samples without bioactive-glass; however, the degradation was remarkably reduced by addition of bioactive-glass. In addition, formation of apatite particles, the main inorganic constituent of the bone, on the surface of the bioactive-glass containing scaffolds were confirmed after immersion in simulated body fluid (SBF). The viability of hMSC on the scaffold suggested that gelatin/bioactive-glass/nanosilver scaffolds can be used as an antibacterial scaffolds.

Asunto(s)

Implantes Absorbibles , Antiinfecciosos/administración & dosificación , Sustitutos de Huesos , Cerámica/química , Nanopartículas del Metal/química , Plata/administración & dosificación , Andamios del Tejido , Antiinfecciosos/efectos adversos , Antiinfecciosos/química , Fenómenos Fisiológicos Bacterianos/efectos de los fármacos , Líquidos Corporales/química , Sustitutos de Huesos/administración & dosificación , Sustitutos de Huesos/efectos adversos , Sustitutos de Huesos/química , Supervivencia Celular/efectos de los fármacos , Cerámica/efectos adversos , Diseño de Equipo , Análisis de Falla de Equipo , Gelatina/efectos adversos , Gelatina/química , Humanos , Ensayo de Materiales , Nanopartículas del Metal/efectos adversos , Nanopartículas del Metal/ultraestructura , Nanocápsulas/efectos adversos , Nanocápsulas/química , Nanocápsulas/ultraestructura , Plata/efectos adversos , Plata/química , Ingeniería de Tejidos/instrumentación

RESUMEN

In this paper, the biocompatibility of a medical-grade stainless steel coated with sol-gel derived, nanostructured inorganic ZrTiO4 and hybrid ZrTiO4-PMMA thin films is correlated with surface characteristics. The surfaces of the samples are characterized by atomic force microscopy, the sessile drop technique, and electrochemical corrosion experiments. The viability of adult human mesenchymal stem cells on the surfaces after one day of culture is also assessed quantitatively and morphologically. According to the results, both of the coatings improve the hydrophilicity, corrosion resistance, and thereby cytocompatibility of the substrate. Despite the higher corrosion protection by the hybrid coating, the sample coated with the inorganic thin film exhibits a better cell response, suggesting the domination of wettability. In summary, the ZrTiO4-based sol-gel films can be considered to improve the biocompatibility of metallic implants.

Asunto(s)

Materiales Biocompatibles Revestidos/síntesis química , Óxidos/farmacología , Polimetil Metacrilato/farmacología , Prótesis e Implantes , Acero Inoxidable/química , Titanio/farmacología , Circonio/farmacología , Adulto , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Materiales Biocompatibles Revestidos/química , Humanos , Ensayo de Materiales , Células Madre Mesenquimatosas/efectos de los fármacos , Células Madre Mesenquimatosas/fisiología , Equipo Ortopédico , Óxidos/química , Transición de Fase , Polimetil Metacrilato/química , Acero Inoxidable/farmacología , Propiedades de Superficie/efectos de los fármacos , Titanio/química , Circonio/química

RESUMEN

The mechanism for phonon scattering by nanostructures and by point defects in nanostructured silicon (Si) and the silicon germanium (Ge) alloy and their thermoelectric properties are investigated. We found that the thermal conductivity is reduced by a factor of 10 in nanostructured Si in comparison with bulk crystalline Si. However, nanosize interfaces are not as effective as point defects in scattering phonons with wavelengths shorter than 1 nm. We further found that a 5 at. % Ge replacing Si is very efficient in scattering phonons shorter than 1 nm, resulting in a further thermal conductivity reduction by a factor of 2, thereby leading to a thermoelectric figure of merit 0.95 for Si95Ge5, similar to that of large grained Si80Ge20 alloys.