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1.
Nanoscale ; 12(2): 572-583, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31803900

RESUMO

The heating ability upon application of an alternating magnetic field of a system of monodisperse and non-interacting superparamagnetic nanoparticles is described by Rosensweig's model within the linear response limits. But in real applications, nanoparticle systems are rarely monodisperse or non-interacting, and predicting their heating ability is challenging, since it requires considering single-particle, inter-particle and collective effects. Herein we give experimental evidence of a collective effect that invalidates the linear response limits in self-assembled anisotropic arrangements. This effect allows tuning Néel relaxation times and, in turn, blocking temperatures, by just varying the alternating magnetic field amplitude. The analysis of the source magnetic and magnetothermal data leads to the development of an empirical model describing the modified Néel relaxation times in terms of characteristic parameters, whose physical interpretation is discussed. As a result, the dependency of Néel relaxation time on the magnetic field amplitude is assigned to a strong interaction energy contribution created locally by the ordered anisotropic assemblies. The reduction of this energy upon application of higher magnetic fields is related to the loss of preferred orientation of the magnetic moment of nanoparticles within assemblies. Remarkably, this energy contribution does not depend on particle volume distribution, so it does not contribute to widening of the energy barrier distribution of the assemblies, avoiding this detrimental effect of magnetic interactions, and contributing to an excellent heating ability. This work thus provides an analytical framework to analyze or predict the magnetic behavior and heating ability of superparamagnetic nanoparticles displaying collective effects.

3.
ACS Nano ; 9(2): 1408-19, 2015 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-25658023

RESUMO

One current challenge of magnetic hyperthermia is achieving therapeutic effects with a minimal amount of nanoparticles, for which improved heating abilities are continuously pursued. However, it is demonstrated here that the performance of magnetite nanocubes in a colloidal solution is reduced by 84% when they are densely packed in three-dimensional arrangements similar to those found in cell vesicles after nanoparticle internalization. This result highlights the essential role played by the nanoparticle arrangement in heating performance, uncontrolled in applications. A strategy based on the elaboration of nano-objects able to confine nanocubes in a fixed arrangement is thus considered here to improve the level of control. The obtained specific absorption rate results show that nanoworms and nanospheres with fixed one- and two-dimensional nanocube arrangements, respectively, succeed in reducing the loss of heating power upon agglomeration, suggesting a change in the kind of nano-object to be used in magnetic hyperthermia.


Assuntos
Hipertermia Induzida/métodos , Fenômenos Magnéticos , Nanomedicina/métodos , Nanopartículas , Óxido Ferroso-Férrico/química , Ácido Láctico/química , Ácido Poliglicólico/química , Copolímero de Ácido Poliláctico e Ácido Poliglicólico , Dióxido de Silício/química
4.
Chemistry ; 20(26): 7956-61, 2014 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-24807735

RESUMO

Fe(II)(Metz)6](Fe(III)Br4)2 (Metz = 1-methyltetrazole) is one of the rare systems combining spin-crossover and long-range magnetic ordering. A joint neutron and X-ray diffraction and magnetometry study allows determining its collinear antiferromagnetic structure, and shows an increase of the Néel temperature from 2.4 K at ambient pressure, to 3.9 K at 0.95 GPa. Applied pressure also enables a full high-spin to low-spin switch at ambient temperature.

5.
Int J Hyperthermia ; 29(8): 739-51, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24001056

RESUMO

In magnetic hyperthermia, characterising the specific functionality of magnetic nanoparticle arrangements is essential to plan the therapies by simulating maximum achievable temperatures. This functionality, i.e. the heat power released upon application of an alternating magnetic field, is quantified by means of the specific absorption rate (SAR), also referred to as specific loss power (SLP). Many research groups are currently involved in the SAR/SLP determination of newly synthesised materials by several methods, either magnetic or calorimetric, some of which are affected by important and unquantifiable uncertainties that may turn measurements into rough estimates. This paper reviews all these methods, discussing in particular sources of uncertainties, as well as their possible minimisation. In general, magnetic methods, although accurate, do not operate in the conditions of magnetic hyperthermia. Calorimetric methods do, but the easiest to implement, the initial-slope method in isoperibol conditions, derives inaccuracies coming from the lack of matching between thermal models, experimental set-ups and measuring conditions, while the most accurate, the pulse-heating method in adiabatic conditions, requires more complex set-ups.


Assuntos
Hipertermia Induzida/métodos , Nanopartículas/uso terapêutico , Animais , Temperatura Alta , Humanos , Fenômenos Magnéticos
6.
Nanoscale ; 4(13): 3954-62, 2012 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-22653748

RESUMO

The heating and self-regulating abilities of La(1-x)Sr(x)MnO(3+Δ) ferromagnetic nanoparticles for magnetic fluid hyperthermia are studied. The samples, synthesized by the Glycine Nitrate Process, present non-agglomerated particles but are partially constituted by polycrystalline nanoparticles, displaying average crystallite diameters ranging from 21 to 31 nm. The strontium content of these nanoparticles, between 0.14 and 0.39, is associated with non-stoichiometry effects in the materials, and both govern their Curie temperatures (T(C)), which range between 13 and 86 °C, respectively. Heating experiments carried out on samples suspended in an aqueous agarose gel and with different alternating magnetic fields derive unexpected maximum temperatures that cannot be explained on the basis of static magnetization data. The measurement of the thermal dependence of the specific absorption rate (SAR) of nanopowders by adiabatic magnetothermia reveals the existence of a dissipation peak just below T(C), which is assigned to a Hopkinson peak. This thermal dependence of SAR, together with a simple thermal model that considers a linear approximation for the heat power losses, is crucial to clarify the behavior observed in heating experiments and also to discuss the possibilities of the samples as self-regulating hyperthermia mediators. This analysis emphasizes that, for the correct design of a self-regulating system, the heat power losses determined by the surrounding conditions must be taken into account as well as the heating capacity of the magnetic nanoparticles.


Assuntos
Compostos de Cálcio/química , Nanopartículas de Magnetita/química , Óxidos/química , Titânio/química , Campos Magnéticos , Polipropilenos/química , Temperatura
7.
Chem Commun (Camb) ; 48(61): 7604-6, 2012 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-22735620

RESUMO

The first tetrahaloferrate spin crossover compound, [Fe(Metz)(6)](FeBr(4))(2) (Metz = 1-methyltetrazole), is reported. The FeBr(4)(-) ions form ferromagnetically coupled 1D stacks and exhibit an antiferromagnetic order at 2.2 K, which coexists with the gradual spin crossover centred at 165 K.

8.
Emergencias (St. Vicenç dels Horts) ; 20(5): 335-342, sept.-oct. 2008. ilus
Artigo em Espanhol | IBECS | ID: ibc-67480

RESUMO

Como medio de mejora de la baja productividad investigadora de calidad en medicina de urgencias, se puede recurrir a la cooperación y al conocimiento de los sistemas de evaluación de los organismos financiadores. Con dicho propósito se presenta una descripción de los dos principales sistemas de evaluación empleados por los organismos financiado esa nivel nacional (FIS) y a nivel europeo (Programas de Cooperación en Salud del Séptimo Programa Marco). Las dimensiones seleccionadas para el análisis fueron: la metodología, el proceso y los criterios de evaluación, el peso del criterio y las características de los evaluadores. Existen diferencias tanto a nivel organizativo, objetivos, política, asignación de recursos, mecanismo de financiación, importancia otorgada a la actividad investigadora, organización de los procesos de investigación y gestión de la investigación, que dificultan la comparación en materia de investigación. Las limitaciones detectadas afectan, entre otras, a la falta de retorno a los evaluadores, la ausencia de confidencialidad sobre los equipos y al déficit de mecanismos de homogeneización de criterios entre evaluadores a lo largo del tiempo (AU)


The knowledge available in the evaluation systems that funding agencies set up to review applications can be taken advantage of to increase the amount of well-designed research in emergency medicine, improving the current situation of low productivity. To further that end, we describe the 2 main review systems used by the Spanish national funding agency and the European Seventh Framework Programme for health research. The dimensions analyzed were as follows: procedures, processes and evaluation criteria; criterion weighting; and characteristics of reviewers. The 2 systems differ in terms of general organization, objectives, policies, allocation of resources, funding mechanisms, importance placed on research productivity, organization of research processes and management. Comparison is therefore difficult. Limitations detected include the lack of feedback for reviewers, of blinding, and of mechanisms to guarantee that evaluation criteria are applied consistently by reviewers over time (AU)


Assuntos
Pesquisa/métodos , Pesquisa/organização & administração , Serviços Médicos de Emergência/métodos , Emergências/epidemiologia , Estudo de Avaliação , Avaliação de Processos e Resultados em Cuidados de Saúde/organização & administração , Avaliação de Processos e Resultados em Cuidados de Saúde , Projetos de Pesquisa/estatística & dados numéricos , Projetos de Pesquisa/tendências , Hospitais de Emergência/organização & administração , Hospitais de Emergência/estatística & dados numéricos
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