Luisa Ruiz-González

Revisiting silica based ordered mesoporous materials : medical applications

The bioactivity behaviour of SBA-15, MCM-48, MCM-41 mesoporous materials, is revisited in this paper. The influence of their different textural and structural properties on apatite formation is outlined and strategies to modify their kinetics are proven and discussed. On the basis of the experimental data showing the feasibility of control of the bioactivity kinetics on mesoporous materials, together with their controlled drug release abilities, new possibilities for tissue engineering developments are proposed.

The dissolution and biological effects of silver nanoparticles in biological media

Silver ions and silver nanoparticles have a well-known biological effect that typically occurs in biological or environmental media of complex composition. Silver nanoparticles release silver ions if oxidizing species like molecular oxygen or hydrogen peroxide are present. The presence of glucose as a model for reducing sugars has only a small effect on the dissolution rate. In the presence of chloride ions, precipitation of silver chloride nanoparticles occurs. At physiological salt concentrations, no precipitation of silver phosphate occurs as the precipitation of silver chloride always occurs first. If the surface of a silver nanoparticle is passivated by cysteine, the dissolution is quantitatively inhibited. Upon immersion of silver nanoparticles in pure water for 8 months, leading to about 50% dissolution, no change in the surface was observed by transmission electron microscopy. A model for the dissolution was derived from immersion and dissolution experiments in different media and from high-resolution transmission electron microscopy. A literature survey on the available data on the dissolution of silver nanoparticles showed that only qualitative trends can be identified as the nature of the nanoparticles and of the immersion medium are practically never comparable. The dissolution effects were confirmed by cell culture experiments (human mesenchymal stem cells and neutrophil granulocytes) where silver nanoparticles that were stored under argon had a clearly lower cytotoxicity than those stored under air. They also led to a less formation of reactive oxygen species (ROS). This underscores that silver ions are the toxic species.

Calcium phosphate nanoparticles as templates for nanocapsules prepared by the layer-by-layer technique

Uniform nanocapsules with typical diameters of 150–240 nm were prepared with calcium phosphate nanoparticles as a fully biocompatible core material by alternate coating with cationic (PAH) and anionic (PSS) polymers (layer-by-layer technique: LbL), followed by dissolution of the calcium phosphate core with hydrochloric acid by dialysis in the presence of ion exchangers. The nanocapsules were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and atomic force microscopy (AFM).

Mechanically Interlocked Single-Wall Carbon Nanotubes†

Extensive research has been devoted to the chemical manipulation of carbon nanotubes. The attachment of molecular fragments through covalent-bond formation produces kinetically stable products, but implies the saturation of some of the C-C double bonds of the nanotubes. Supramolecular modification maintains the structure of the SWNTs but yields labile species. Herein, we present a strategy for the synthesis of mechanically interlocked derivatives of SWNTs (MINTs). In the key rotaxane-forming step, we employed macrocycle precursors equipped with two π-extended tetrathiafulvalene SWNT recognition units and terminated with bisalkenes that were closed around the nanotubes through ring-closing metathesis (RCM). The mechanically interlocked nature of the derivatives was probed by analytical, spectroscopic, and microscopic techniques, as well as by appropriate control experiments. Individual macrocycles were observed by HR STEM to circumscribe the nanotubes.

Band gap opening in metallic single-walled carbon nanotubes by encapsulation of an organic salt

The encapsulation of viologen derivatives into metallic single-walled carbon nanotubes (SWNTs) results in the opening of a band gap, making the SWNTs semiconducting. Raman spectroscopy, thermogravimetric analysis, and aberration-corrected high-resolution transmission electron microscopy confirm the encapsulation process. Through the fabrication of field-effect transistor devices, the change of the electronic structure of the tubes from metallic to semiconducting upon the encapsulation is confirmed. The opening of a gap in the band structure of the tubes was not detected in supramolecular controls.

Revisiting the Role of Vacancies in Manganese Related Perovskites

Oxygen engineering is an important tool for on-demand tailoring of manganese related perovskites into opti- mized performances. Anionic vacancies can be induced in both doped and undoped manganites by means of topotactic re- duction processes under oxygen controlled atmosphere. This has given rise to the stabilization of new phases as a conse- quence of ordering of oxygen vacancies in which Mn 2+ appears due to the reducing process. Different reduction pathways are proposed for LaMnO3 and doped systems. FM interactions remain at the octahedral layers when vacancies are long- range ordered. The peculiar magnetic behaviour of new layered perovskite superstructures is discussed.