Robocasting and Laser Micromachining of Sol-Gel Derived 3D Silica/Gelatin/ß-TCP Scaffolds for Bone Tissue Regeneration.

The design and synthesis of sol-gel silica-based hybrid materials and composites offer significant benefits to obtain innovative biomaterials with controlled porosity at the nanostructure level for applications in bone tissue engineering. In this work, the combination of robocasting with sol-gel ink of suitable viscosity prepared by mixing tetraethoxysilane (TEOS), gelatin and ß-tricalcium phosphate (ß-TCP) allowed for the manufacture of 3D scaffolds consisting of a 3D square mesh of interpenetrating rods, with macropore size of 354.0 ± 17.0 µm, without the use of chemical additives at room temperature. The silica/gelatin/ß-TCP system underwent irreversible gelation, and the resulting gels were also used to fabricate different 3D structures by means of an alternative scaffolding method, involving high-resolution laser micromachining by laser ablation. By this way, 3D scaffolds made of 2 mm thick rectangular prisms presenting a parallel macropore system drilled through the whole thickness and consisting of laser micromachined holes of 350.8 ± 16.6-micrometer diameter, whose centers were spaced 1312.0 ± 23.0 µm, were created. Both sol-gel based 3D scaffold configurations combined compressive strength in the range of 2-3 MPa and the biocompatibility of the hybrid material. In addition, the observed Si, Ca and P biodegradation provided a suitable microenvironment with significant focal adhesion development, maturation and also enhanced in vitro cell growth. In conclusion, this work successfully confirmed the feasibility of both strategies for the fabrication of new sol-gel-based hybrid scaffolds with osteoconductive properties.

Laser-Assisted Synthesis of Colloidal FeWx Oy and Fe/Fex Oy Nanoparticles in Water and Ethanol.

Homogeneous polycrystalline Fex Oy nanoparticles were generated by ablation of iron targets in water by nanosecond laser pulses at 532 nm. In ethanol, crystalline core-shell Fe/Fex Oy structures with size medians around 20 nm were produced. The ablation of FeWx Oy targets in water resulted in crystalline hollow shells and homogeneous FeWx Oy nanoparticles. In contrast, amorphous core-shell FeWx Oy nanoparticles with a median size of 17 nm were produced in ethanol. The size distribution of both the Fex Oy and the FeWx Oy particles showed a slight dependence on fluence and pulse number. This may be related to primary and secondary ablation and modification mechanisms.

Laser-Assisted Synthesis of Colloidal Ni/NiOx Core/Shell Nanoparticles in Water and Alcoholic Solvents.

The nanosecond-pulse laser-assisted generation of Ni/NiOx core/shell nanoparticles (NPs) in water and alcoholic fluids can yield colloidal solutions without surfactants. The size distribution can be controlled by the nature of the alcohol, the number of laser pulses and the laser fluence. The incubation of the nickel target ablation in liquid contact shows a dependence on the carbon number of the respective alcohol. The laser-generated NPs consist of crystalline nickel cores with face-centred cubic patterns and stacking fault defects surrounded by nickel oxide shells. The solvent butanol, in contrast to ethanol and isopropanol, yields a narrow, nearly unimodal, size distribution. The majority of NPs have low size distributions, with medians in the range of 10-20 nm. These can be related to a metal ablation plume interacting with a supercritical liquid that decelerates the ejected material in a low-density metal-water mixing region. NPs in the range above 30 nm result in a minority distribution tail that strongly depends on the fluid nature, the pulse number and the fluence. This coarse NP set may be correlated with the rupture of a superheated molten-metal layer into larger entities.

A new ex vivo method to evaluate the performance of candidate MRI contrast agents: a proof-of-concept study.

BACKGROUND: Magnetic resonance imaging (MRI) plays an important role in tumor detection/diagnosis. The use of exogenous contrast agents (CAs) helps to improve the discrimination between lesion and neighbouring tissue, but most of the currently available CAs are non-specific. Assessing the performance of new, selective CAs requires exhaustive assays and large amounts of material. Accordingly, in a preliminary screening of new CAs, it is important to choose candidate compounds with good potential for in vivo efficiency. This screening method should reproduce as close as possible the in vivo environment. In this sense, a fast and reliable method to select the best candidate CAs for in vivo studies would minimize time and investment cost, and would benefit the development of better CAs. RESULTS: The post-mortem ex vivo relative contrast enhancement (RCE) was evaluated as a method to screen different types of CAs, including paramagnetic and superparamagnetic agents. In detail, sugar/gadolinium-loaded gold nanoparticles (Gd-GNPs) and iron nanoparticles (SPIONs) were tested. Our results indicate that the post-mortem ex vivo RCE of evaluated CAs, did not correlate well with their respective in vitro relaxivities. The results obtained with different Gd-GNPs suggest that the linker length of the sugar conjugate could modulate the interactions with cellular receptors and therefore the relaxivity value. A paramagnetic CA (GNP (E_2)), which performed best among a series of Gd-GNPs, was evaluated both ex vivo and in vivo. The ex vivo RCE was slightly worst than gadoterate meglumine (201.9 ± 9.3% versus 237 ± 14%, respectively), while the in vivo RCE, measured at the time-to-maximum enhancement for both compounds, pointed to GNP E_2 being a better CA in vivo than gadoterate meglumine. This is suggested to be related to the nanoparticule characteristics of the evaluated GNP. CONCLUSION: We have developed a simple, cost-effective relatively high-throughput method for selecting CAs for in vivo experiments. This method requires approximately 800 times less quantity of material than the amount used for in vivo administrations.

Controlled formation of porous magnetic nanorods via a liquid/liquid solvothermal method.

Porous magnetic nanorods with sizes readily modulated and high water affinity are prepared via a water-in-oil/water solvothermal method.

Direct aerosol synthesis of carboxy-functionalized iron oxide colloids displaying reversible magnetic behavior.

A simple and rapid synthetic strategy for fabricating carboxy-functionalized iron oxide colloidal particles displaying reversible magnetic behavior is reported. The method is based on the pyrolysis of aerosols generated from ethanol/water solutions containing iron inorganic salts and mono- or polysaccharides. Essential to the success of the method are the use of hybrid (organo-inorganic) aerosols and the temperature of pyrolysis. The resulting material could be used in advanced biotechnological applications such as the magnetically assisted chemical separation of biocompounds.

Core-shell iron-iron oxide nanoparticles synthesized by laser-induced pyrolysis.

Passivated iron nanoparticles (10-30 nm) have been synthesized by laser pyrolysis of a mixture of iron pentacarbonyl and ethylene vapors followed by controlled oxidation. The nanoparticles show a well-constructed iron-iron oxide core-shell structure, in which the thickness and nature (structure similar to maghemite, gamma-Fe2O3) of the shell is found to be independent of the initial conditions. On the other hand, the composition of the core is found to change with the particle size from the alpha-Fe structure to a highly disordered Fe phase (probably containing C atoms in its structure). The dependence of the magnetic properties on the particle size, iron oxide fraction, and temperature was also investigated. In the case of smaller particles, the magnetic data indicate the existence at low temperature of a large exchange anisotropy field, the magnitude of which increases with decreasing temperature in correspondence with the freezing of magnetic moments in the oxide shell.

Fe-based nanoparticulate metallic alloys as contrast agents for magnetic resonance imaging.

Pharmaceutical grade magnetic colloidal dispersions have been prepared from iron alloys synthesized by laser pyrolysis. The colloids were obtained by simultaneous dispersion and coating of the particles with dextran in a strong alkaline solution. Both powders and dispersions have been analyzed in terms of microstructural characteristics, chemical composition and magnetic properties. The powders consist of uniform spherical nanoparticles (12 nm of diameter) showing a metallic core encapsulated into an iron-oxide shell. On the other hand, the colloidal dispersions consist of magnetic particles-aggregates with hydrodynamic sizes of approximately 75 nm. Magnetic resonance images of rats were taken after the intravenously administration of the Fe colloidal dispersions, and compared with those obtained using a commercial iron oxide magnetic resonance imaging contrast agent. The results showed a contrast improvement of 60% in the liver with respect to the commercial sample, which suggests that this product could be a suitable contrast agent for NMR imaging of liver and spleen.