Luca Bertinetti

Intrinsic magnetism and hyperthermia in bioactive Fe-doped hydroxyapatite

The use of magnetic activation has been proposed to answer the growing need for assisted bone and vascular remodeling during template/scaffold regeneration. With this in mind, a synthesis procedure was developed to prepare bioactive (Fe2+/Fe3+)-doped hydroxyapatite (Fe-HA), endowed with superparamagnetic-like properties. This new class of magnetic hydroxyapatites can be potentially employed to develop new magnetic ceramic scaffolds with enhanced regenerative properties for bone surgery; in addition, magnetic Fe-HA can find application in anticancer therapies, to replace the widely used magnetic iron oxide nanoparticles, whose long-term cytotoxicity was recently found to reach harmful levels. An extensive physicochemical, microstructural and magnetic characterization was performed on the obtained Fe-HA powders, and demonstrated that the simultaneous addition of Fe2+ and Fe3+ ions during apatite nucleation under controlled synthesis conditions induces intrinsic magnetization in the final product, minimizing the formation of magnetite as secondary phase. This result potentially opens new perspectives for biodevices aimed at bone regeneration and for anti-cancer therapies based on hyperthermia.

Surface Characteristics of Nanocrystalline Apatites: Effect of Mg Surface Enrichment on Morphology, Surface Hydration Species, and Cationic Environments

The incorporation of foreign ions, such as Mg2+, exhibiting a biological activity for bone regeneration is presently considered as a promising route for increasing the bioactivity of bone-engineering scaffolds. In this work, the morphology, structure, and surface hydration of biomimetic nanocrystalline apatites were investigated before and after surface exchange with such Mg2+ ions, by combining chemical alterations (ion exchange, H2O-D2O exchanges) and physical examinations (Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM)). HRTEM data suggested that the Mg2+/Ca2+ exchange process did not affect the morphology and surface topology of the apatite nanocrystals significantly, while a new phase, likely a hydrated calcium and/or magnesium phosphate, was formed in small amount for high Mg concentrations. Near-infrared (NIR) and medium-infrared (MIR) spectroscopies indicated that the samples enriched with Mg2+ were found to retain more water at their surface than the Mg-free sample, both at the level of H2O coordinated to cations and adsorbed in the form of multilayers. Additionally, the H-bonding network in defective subsurface layers was also noticeably modified, indicating that the Mg2+/Ca2+ exchange involved was not limited to the surface. This work is intended to widen the present knowledge on Mg-enriched calcium phosphate-based bioactive materials intended for bone repair applications.

On the hydrothermal stability of MCM-41 mesoporous silica nanoparticles and the preparation of luminescent materials

MCM-41 nanoparticles have recently attracted growing scientific interest for applications in biomedical and diagnostic fields, nevertheless their use is limited because of the low hydrothermal stability, rendering them not suitable for functionalisation (i.e. dye molecules loading, anchoring of luminescent guests, etc.) in aqueous media. In this work, nanosized MCM-41 was hydrothermally stabilised by properly adapting post-synthesis hydrothermal restructuring treatment already used for conventional MCM-41 material (particle size in the micron range). A significant improvement of the hydrothermal stability of nanosized MCM-41 was reached: the pore array of the stabilized MCM-41 was not significantly modified after hydrothermal treatment at 333 K, whereas under the same conditions the parent MCM-41 became partially amorphized. The hydrothermal stabilisation is due to pore wall restructuring occurring during post-synthesis modification, and an increase of hydrophobicity of the silica surface. The improved hydrothermal stability of nanosized MCM-41 rendered this solid suitable for dye impregnation in aqueous media and allowed the preparation of a luminescent fluorescein/MCM-41 nanocomposite material, which in aqueous suspension showed an emission efficiency 5 times higher than an equimolar fluorescein solution.

On the acidity of saponite materials: a combined HRTEM, FTIR, and solid-state NMR study.

Acid clays were prepared by exchanging a synthetic saponite in HCl solutions of different concentration (0.01 and 1M, respectively). A combined experimental approach (XRD, HRTEM, N2 physisorption, solid-state MAS NMR, and TGA) was used to investigate on the structural, morphological, and textural features of the samples treated under mild and strong acid conditions. FTIR spectroscopy of adsorbed probe molecules with different basicity (e.g., CO and NH3) was used to monitor the surface acid properties and acid site distribution. XRD and SS-MAS NMR indicated that the activation under mild acid conditions does not alter the clay structure, while a deep modification of the saponite framework occurred after ion exchange in 1 M HCl solution. The presence of porous amorphous silica phase after treatment under strong acid conditions was confirmed by TEM inspection augmented by SS-MAS NMR and FTIR spectroscopy. N2 and Ar physisorption measurements suggested that cavitation phenomena occurred in saponite structure. N2 physisorption confirmed that the porosity and surface area of the samples are strongly modified upon strong acid treatment. FTIR spectroscopy of adsorbed NH3 pointed out that the H-exchange in mild conditions increased the number of surface Brønsted acid sites. Conversely, these sites are significantly depleted after treatment under strong acid conditions. The use of CO as a FTIR probe molecule, which is applied for the first time to study synthetic acid clays, allowed to monitor distribution and strength of Brønsted acid sites, whose acidity is similar to that of strong acid zeolites. The Al-OH sites with medium acidity are also found in acid-activated saponites. The distribution of strong and medium acid sites is strictly dependent on the acid conditions adopted.

Biofunctionalization of anisotropic nanocrystalline semiconductor-magnetic heterostructures.

Asymmetric binary nanocrystals (BNCs) formed by a spherical γ-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications.

A Waste‐Derived Biosurfactant for the Preparation of Templated Silica Powders

A polymeric anionic biosurfactant isolated from urban bio-wastes was used as a template for fabricating silica powders of pore size ranging from 4 to 30 nm by the sol-gel reaction of tetraethylorthosilicate and 3-aminopropyltriethoxysilane at pH 5. The morphology of the synthesized silica powders was found to depend on the size and the conformation of the biosurfactant molecules or aggregates in solution. The use of waste-derived biosurfactants as templating agents reduces the fabrication costs and the environmental impact of mesoporous materials. At the same time, it encourages the upgrade of bio-wastes from a costly disposal matter to a source of chemicals and therefore, of revenue.

Surface Structure, Hydration and Cationic Sites of Nanohydroxyapatite

In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

Development of Multisubstituted Apatites for Bone Reconstruction

Hydroxyapatite powders characterized by substitutions of Mg2+, SiO4 4-, CO3 2- ions in biological like amounts, in the crystallographic site of calcium and phosphates, ions in biological like amounts, in the crystallographic site of calcium and phosphorus, were successfully prepared by synthesis in aqueous medium. The chemico-physical properties of the powders were investigated through several analytical techniques, among them: XRD, FTIR, TG-DTA, ICP-OES, HR-TEM. The entering of silicon in the HA structure progressively reduces its crystallinity, as also carbonate ions do. Silicate and carbonate ions can enter simultaneously into the HA structure, in biological-like amounts, although they compete for the occupation of the phosphate site. Solubility tests, carried out at physiological conditions, reveal an increased calcium release in the HA powders containing silicon compared to the silicon-free HA.

EXAFS and XANES structural characterization of bimetallic AuPd vapor derived catalysts

Using an innovative procedure known as metal vapor synthesis (MVS) to prepare bimetallic catalysts, starting from Au and Pd vapors, [AuPd] co-evaporated and [Au][Pd] separately evaporated bimetallic catalysts were achieved. After being tested, the catalytic activity and selectivity of the [AuPd] catalyst turned out to be higher than the [Au][Pd] ones. Using EXAFS spectroscopy it was shown that, in the [AuPd] samples, small bimetallic AuPd nanoparticles were present, having an Au rich core surrounded by an AuPd alloyed shell while in the [Au][Pd] sample there was the presence of monometallic Au and Pd nanoparticles showing some alloying only in the boundary regions. The EXAFS results were also qualitatively confirmed by the XANES spectra.

In vitro bio-mineralization process

The present work describes the development of biomimetic composites materials for bone tissue substitution and repair. At this purpose a biomimetic approach was used and apatitic phases were nucleated on macromolecular matrices like natural collagen, which act as template and induce peculiar physico-chemical features in the mineral phase.