L. Ruiz

The influence of proteins on the dispersability and cell-biological activity of silver nanoparticles

Spherical silver nanoparticles with a diameter of 50 ± 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI–BSA mixture within a few hours, the particles remained well dispersed in RPMI–FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI–BSA and RPMI–FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins.

Calcium phosphate nanoparticles with adjustable dispersability and crystallinity

Approximately spherical calcium phosphate nanoparticles with a diameter of about 50 nm can be prepared by rapid precipitation from water and subsequent colloidal stabilization by coating with polymers (polyvinylpyrrolidone, PVP, and polyethyleneimine, PEI). If they are either washed with isopropanol followed by air-drying, or freeze-dried, they can be easily redispersed in polar organic solvents in colloidal form. High-resolution transmission electron microscopy (HRTEM) and electron diffraction showed that their internal crystallinity depends on the drying method: After freeze-drying, the particles remain amorphous whereas all other drying methods lead to nanocrystalline particles. TEM observations also suggest a disordered surface layer (with a thickness of about 5 nm) of the crystalline particles, consisting of hydroxyapatite and calcium oxide. The presence of calcium oxide was ascribed to a surface layer of calcium carbonate that was formed by precipitation in a hydrated surface layer from atmospheric carbon dioxide and then decarboxylated in the TEM. In conclusion, we show how calcium phosphate nanoparticles can be prepared with defined crystallinity and dispersability while their external size and shape are retained.

An injectable paste of calcium phosphate nanorods, functionalized with nucleic acids, for cell transfection and gene silencing

Calcium phosphate nanorods which are typically used as paste for bone substitution were functionalized by DNA or siRNA. The structure and morphology of the nanorods did not change by the functionalization as indicated by dynamic light scattering (DLS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). With a load of nucleic acids of about 2.7 wt%, the nanorods were used for transfection with HeLa and T24 cells, and for gene silencing with HeLa-EGFP cells. Removal of the water by filtration gave an injectable paste with a content of nucleic acids of about 2 wt%, and a water content of 43 wt%. This leads to a bioactive paste as hard-tissue regeneration material.

Perpendicular magnetic anisotropy in Co-Pt granular multilayers

Magnetization hysteresis curves have been measured on Co granular multilayers, (Al2O3/Co/Pt)N (N = 1 and 25), with the applied magnetic field parallel and perpendicular to the substrate plane. In all samples perpendicular magnetic anisotropy was observed. For Co particles with average diameter 3 nm, the coercive field at low temperature is μ0HC = 0.5 T. HC decreases for increasing temperature and disappears at ≈200 K. A soft magnetic component is also present in all samples up to the freezing temperature Tf = 365 K. Co and Pt XMCD measurements at the L2,3 edges were performed, yielding to the orbital mL and spin mS contributions to the total magnetic moment of the system. These results, in addition to XANES ones, indicate the presence of CoxPt1−x alloy. Particles conformed of CoPt alloy, embedded in Pt and coupled magnetically by dipolar or RKKY interaction, may explain the phenomenology observed in these systems.

Morphology and magnetic properties of W-capped Co nanoparticles

Co–W nanoparticles formed by sequential sputtering of Co on amorphous alumina substrate and subsequent W capping are studied by high resolution and by scanning transmission electron microscopies, and by superconducting quantum interference device magnetometry. The analysis is focused on W nominal thickness dependence. Results suggest the formation of amorphous Co–W alloy nanoparticles, whose magnetic moment per Co atom is systematically reduced as the nominal thickness of W capping layer increases. The Co–W nanoparticles show superparamagnetic behavior. The activation energy for moment reversal and the effective anisotropy are obtained.

Syntesis of Mesoporous Microparticles for Biomedical Applications

Towards the design of bioceramics with control over both macroscopic shape and mesoporosity, silica based mesoporous materials have been synthesized using evaporation-induced self-assembly method by two different routes: room temperature (RT) and aerosol-assisted synthesis (A-A). Two series varying surfactant/silica precursor ratio have been synthesized in order to check the mesopore ordering as a function of the structure directing agent amount in both preparation procedures. The A-A method leads to spherical microparticles, which exhibit mesopore ordering for a wider surfactant/silica range compared with room temperature method, which yield irregular shaped particles. Textural properties values show that for the same surfactant amount, aerosol-assisted method develops higher porosity values in the obtained silica microparticles.