Читать книгу Magnetic Nanoparticles in Human Health and Medicine - Группа авторов - Страница 46

Various preparation methods of magnetic clusters considered inorganic coatings for the stabilization of multistructures. The magnetic nanoparticles encapsulation within a silica sphere is one of the most followed approaches, as described and developed by Taboada et al. First, the nanoparticles were aggregated in a controlled manner by a sol‐gel method in a mixture of acetone and hexane. The magnetic clusters served as nucleation sites for the subsequent condensation of hydrolyzed tetramethoxy silane (TMOS), leading to the formation of the silica shell. The obtained structures had a diameter of approximately 100 nm, and the production of grams of magnetic clusters was demonstrated (Taboada et al. 2009). Also, Niu et al. chose the encapsulation into silica for the preparation of their nanocomposite (Niu et al. 2010). By using an oil‐in‐water approach, the hydrophobic magnetic nanoparticles were first incorporated into the copolymer micelles core composed of polystyrene₁₀₀‐block‐poly(acrylic acid)₁₆. Therefore, a silica layer was grown on top of the micelles by using 3‐mercaptopropyltrimethoxysilane (MPMTS) as priming molecule. Also, in that case, nanostructures with a final diameter smaller than 100 nm were fabricated.

Kralj and Makovec (2015) assessed the preparation of superparamagnetic nanostructures with highly anisotropic shapes, called nanochains. In this work, their group used some commercial nanoclusters, obtained through a nanoemulsion process and finally stabilized by a tuned silica shell. These nanostructures were formed by interaction between nanoclusters and a controlled magnetic field in presence of PVP molecules. By this way, the authors achieved the formation of small chains composed of different monomers, by tuning the field strength and exposure duration, the PVP concentration, and the stirring speed. The purpose of this clustering approach should lead to applications of the nanochains in the cancer treatment and in the ability to magnetically manipulate liquid and photonic crystals (Kralj and Makovec 2015).

Recently, Tregubov et al. used a metal‐organic framework as a substrate for the magnetic nanoclusters coating. The authors used the citrate‐capped iron oxide nanoparticles as starting material, obtained by autoclave and by using urea as precipitant. This magnetic core with a size of 80 nm and composed by several single magnetic domains was further coated by a matrix of iron(III) trimesate (also known as MIL‐100(Fe)) and synthesized by autoclaving the mixture of nanoparticles and metal precursor. Finally, a carboxymethyl dextran layer was grafted onto the surface of the system for achieving optimal colloidal stability. An advantage of such multilayered object was the assessed biocompatibility since the iron(III) trimesate can be readily degraded in physiological conditions because of the collapse of the framework in the presence of phosphates (Tregubov et al. 2018).