A concise review of nanomaterials for drug delivery and release

This review provides an updated vision about the recent developments in the field of drug vectorization using functional nanoparticles and other nanovectors. From a large number of these nanotechnology-based drug delivery systems that emerge nearly every week, only a tiny fraction reaches a pre-clinical or clinical phase study. In this report, we intend to provide contextual information about those nanocarriers and release methods that have shown the best outcomes at in vitro and in vivo experiments, highlighting those with proven therapeutic efficiency in humans. From silica-based porous nanoparticles to liposomes or polymeric nanoparticles, each one of these nanosystems has its advantages and drawbacks. We describe and discuss briefly those approaches that, in our criterion, have provided significant advancements over existing therapies at the in vivo level. This work also provides a general view of those commercially available nanovectors and their specific area of therapeutic action

The effect of the magnetically dead layer on the magnetization and the magnetic anisotropy of the dextran-coated magnetite nanoparticles

We present a study on the magnetic behavior of dextran-coated magnetite nanoparticles (DM NPs) with sizes between 3 and 19 nm, synthesized by hydrothermal-assisted co-precipitation method. The decrease of saturation magnetization (M-s) with decreasing particle size has been modeled by assuming the existence of a spin-disordered layer at the particle surface, which is magnetically dead. Based on this core-shell model and taking into account the weight contribution of non-magnetic coating layer (dextran) to the whole magnetization, the dead layer thickness (t) and saturation magnetization M-s of the magnetic cores in our samples were estimated to be t = 6.8 angstrom and M-s = 98.8 emu/g, respectively. The data of M-s were analyzed using a law of approach to saturation, indicating an increase in effective magnetic anisotropy (K-eff) with decreasing the particle size as expected from the increased surface/volume ratio in small MNPs. The obtained K-eff values were successfully modeled by including an extra contribution of dipolar interactions due to the formation of chain-like clusters of MNPs. The surface magnetic anisotropy (K-s) was estimated to be about K-s = 1.04x10(5) J/m(3). Our method provides a simple and accurate way to obtain the M-s core values in surface-disordered MNPs, a relevant parameter required for magnetic modeling in many applications. GRAPHICS]

Synthesis and characterization of nanoparticles of MFe2O4 (M=Fe, CO, Ni) for application in magnetic hyperthermia

Las nanopartículas magnéticas de óxido de hierro constituyen en la actualidad uno de los sistemas más prometedores dentro del campo de la biomedicina. Debido a las novedosas propiedades que presentan, su estudio se ha convertido en una actividad muy importante en la investigación de materiales magnéticos con carácter aplicativo. Por lo tanto, la motivación fundamental para la síntesis y estudio de coloides biocompatibles es el estudio de las propiedades magnéticas derivadas de las dimensiones nanométricas y la relación área superficial contra volumen existente. En el presente trabajo se ha estudiado la preparación de suspensiones coloidales de partículas de magnetita y ferritas de cobalto y níquel para aplicaciones biomédicas, abarcando tanto su síntesis como la caracterización de las propiedades. Para llevar a cabo la síntesis de las partículas se ha estudiado un método muy novedoso como es el de la descomposición térmica de precursores orgánicos de hierro en disolventes orgánicos y en presencia de surfactantes. Este método conduce a nanopartículas magnéticas monodispersas y muy cristalinas cuyo tamaño medio, forma y distribución pueden variar en función de parámetros experimentales como la naturaleza y concentración de los reactivos, además del control de la rampa de temperatura. Las propiedades estructurales de estas partículas son mejores que las obtenidas por métodos más convencionales como la coprecipitación o la pirolisis láser. Dado el carácter hidrófobo de las partículas sintetizadas, éstas no son aptas para su uso en biomedicina por lo que se ha estudiado la transferencia al medio acuoso, consiguiendo obtener suspensiones estables en agua menores de 100 nm. Las nanopartículas obtenidas se evaluaron in vitro como agentes de calentamiento para hipertermia magnética mediante la Absorción Específica de Potencia (SPA). Los valores obtenidos dependen tanto del tamaño de partícula como de la distribución de tamaños. El objetivo global está orientado al desarrollo de una nueva terapia de hipertermia magnética con aplicación en oncología

Estudio de la liberación remota de fármacos mediante campos magnéticos alternos en polímeros termosensibles

La liberación remota de fármacos por hipertermia magnética es una de las terapias experimentales más prometedoras en el campo de la biomedicina. Es posible emplear nanopartículas magnéticas como calentadores en un ferrogel constituido por el polímero termosensible PNIPAM y alginato. La aplicación de un campo magnético alterno sobre dicho ferrogel, en cuyo interior se introduce el fármaco a liberar, ocasiona calentamiento del sistema por hipertermia e induce la liberación del fármaco. En este trabajo se abordan la síntesis y caracterización experimental de nanopartículas magnéticas, y la realización de una prueba de concepto para este tipo de liberación

Long-term stability and reproducibility of magnetic colloids are key issues for steady values of specific power absorption over time

Virtually all clinical applications of magnetic nanoparticles (MNPs) require the formulation of biocompatible, water-based magnetic colloids. For magnetic hyperthermia, the requirements also include a high colloidal stability against precipitation and agglomeration of the constituent MNPs to maintain the heating efficiency of the ferrofluid in the long term. Agglomeration can change the heating efficiency by forming MNP clusters that modify the magnetic dipolar interactions between particles. Additionally, precipitation of the MNPs (i.e., the heating sources within the liquid) can change the measured heating rates of a colloid by altering the heat flow dynamics as the particles plunge to the precipitate. The specific power absorption (SPA) of single-domain MNPs depends critically on the average particle size and size distribution width and therefore first-rate reproducibility of different batches with respect to these parameters is also needed. We have studied the evolution of the SPA of highly reproducible and stable water-based colloids composed of polymer-coated Fe3O4 magnetic nanoparticles. By measuring the specific power absorption (SPA) values for 1 year as a function of field amplitude and frequency (H = 24 kA/m; 260 = f = 830 kHz), we have demonstrated that the SPA values of these samples can be reproduced in successive synthetic batches and stable for several months due to the in situ polymer coating that provides colloidal stability and keeps dipolar interactions negligible

Piconewton Mechanical Forces Promote Neurite Growth

Investigations over half a century have indicated that mechanical forces induce neurite growth, with neurites elongating at a rate of 0.1–0.3 μm h−1 pN−1 when mechanical force exceeds a threshold, with this being identified as 400–1000 pN for neurites of PC12 cells. In this article, we demonstrate that neurite elongation of PC12 cells proceeds at the same previously identified rate on application of mechanical tension of ∼1 pN, which is significantly lower than the force generated in vivo by axons and growth cones. This observation raises the possibility that mechanical tension may act as an endogenous signal used by neurons for promoting neurite elongation