Physicochemical regulation of TGF and VEGF delivery from mesoporous calcium phosphate bone substitutes.

AIM: Determination of the physicochemical parameters governing growth factors (GFs) adsorption and release from mesoporous calcium phosphate ceramics. MATERIALS & METHODS: Six mesoporous calcium phosphate ceramics prepared by soft and hard templating were loaded with two different physiological concentrations of TGF-ß1 or VEGF165 and their in vitro kinetics of adsorption/release were studied. RESULTS: This low GF loading promotes adsorption on the highest binding sites. The usually encountered detrimental burst release is thus considerably reduced for samples prepared by hard-templating method. CONCLUSION: Our findings highlight that the strong affinity of GFs with the ceramic surfaces, demonstrated by a slow GFs release, is enhanced by the large surface area, confinement into mesopores of ceramics and high difference of surface charge between ceramic surfaces and GFs.

Realistic molecular model of kerogen's nanostructure.

Despite kerogen's importance as the organic backbone for hydrocarbon production from source rocks such as gas shale, the interplay between kerogen's chemistry, morphology and mechanics remains unexplored. As the environmental impact of shale gas rises, identifying functional relations between its geochemical, transport, elastic and fracture properties from realistic molecular models of kerogens becomes all the more important. Here, by using a hybrid experimental-simulation method, we propose a panel of realistic molecular models of mature and immature kerogens that provide a detailed picture of kerogen's nanostructure without considering the presence of clays and other minerals in shales. We probe the models' strengths and limitations, and show that they predict essential features amenable to experimental validation, including pore distribution, vibrational density of states and stiffness. We also show that kerogen's maturation, which manifests itself as an increase in the sp(2)/sp(3) hybridization ratio, entails a crossover from plastic-to-brittle rupture mechanisms.

Hydrogen sorption properties of Pd-Co nanoalloys embedded into mesoporous carbons.

Pd90Co10 and Pd75Co25 nanoalloys embedded into mesoporous carbon hosts have been prepared by two synthetic methods: direct and indirect. The average nanoparticles size can be tuned by both the temperature during thermal treatment and the chemical composition: the higher the treatment temperature and the richer the Pd composition, the larger the nanoparticle size. Twofold size- and composition-dependence of the hydrogen sorption properties at room temperature are evidenced. The Co substitution in Pd nanoalloys increases the equilibrium pressure at room temperature relative to nanosized Pd. The hydrogen sorption capacity decreases by Co substitution in Pd, as also demonstrated by SQS + DFT calculations.

In vitro and in vivo evaluation of the inflammatory potential of various nanoporous hydroxyapatite biomaterials.

AIM: To discriminate the most important physicochemical parameters for bone reconstruction, the inflammatory potential of seven nanoporous hydroxyapatite powders synthesized by hard or soft templating was evaluated both in vitro and in vivo. MATERIALS & METHODS: After physical and chemical characterization of the powders, we studied the production of inflammatory mediators by human primary monocytes after 4 and 24 h in contact with powders, and the host response after 2 weeks implantation in a mouse critical size defect model. RESULTS: In vitro results highlighted increases in the secretion of TNF-α, IL-1, -8, -10 and proMMP-2 and -9 and decreases in the secretion of IL-6 only for powders prepared by hard templating. In vivo observations confirmed an extensive inflammatory tissue reaction and a strong resorption for the most inflammatory powder in vitro. CONCLUSION: These findings highlight that the most critical physicochemical parameters for these nanoporous hydroxyapatite are, the crystallinity that controls dissolution potential, the specific surface area and the size and shape of crystallites.

Characterization of carbon surface chemistry by combined temperature programmed desorption with in situ X-ray photoelectron spectrometry and temperature programmed desorption with mass spectrometry analysis.

The analysis of the surface chemistry of carbon materials is of prime importance in numerous applications, but it is still a challenge to identify and quantify the surface functional groups which are present on a given carbon. Temperature programmed desorption with mass spectrometry analysis (TPD-MS) and X-ray photoelectron spectroscopy with an in situ heating device (TPD-XPS) were combined in order to improve the characterization of carbon surface chemistry. TPD-MS analysis allowed the quantitative analysis of the released gases as a function of temperature, while the use of a TPD device inside the XPS setup enabled the determination of the functional groups that remain on the surface at the same temperatures. TPD-MS results were then used to add constraints on the deconvolution of the O1s envelope of the XPS spectra. Furthermore, a better knowledge of the evolution of oxygen functional groups with temperature during a thermal treatment could be obtained. Hence, we show here that the combination of these two methods allows to increase the reliability of the analysis of the surface chemistry of carbon materials.

Microporous carbon adsorbents with high CO2 capacities for industrial applications.

In this study we attempt to investigate the potential use of two zeolite template carbon (ZTC), EMT-ZTC and FAU-ZTC, to capture CO(2) at room temperature. We report their high pressure CO(2) adsorption isotherms (273 K) that show for FAU-ZTC the highest carbon capture capacity among published carbonaceous materials and competitive data with the best organic and inorganic adsorbing frameworks ever-known (zeolites and mesoporous silicas, COFs and MOFs). The importance of these results is discussed in light of mitigation of CO(2) emissions. In addition to these new experimental CO(2) adsorption data, we also present new insight into the adsorption process of the two structures by Monte Carlo simulations: we propose that two separate effects are responsible for the apparent similarity of the adsorption behaviour of the two structures: (i) pore blocking occurring on EMT-ZTC, and (ii) the change of the carbon polarizability due to the extreme curvature of FAU-ZTC.

Synthesis of small metallic Mg-based nanoparticles confined in porous carbon materials for hydrogen sorption.

MgH2, Mg-Ni-H and Mg-Fe-H nanoparticles inserted into ordered mesoporous carbon templates have been synthesized by decomposition of organometallic precursors under hydrogen atmosphere and mild temperature conditions. The hydrogen desorption properties of the MgH2 nanoparticles are studied by thermo-desorption spectroscopy. The particle size distribution of MgH2, as determined by TEM, is crucial for understanding the desorption properties. The desorption kinetics are significantly improved by downsizing the particle size below 10 nm. Isothermal absorption/desorption cycling of the MgH2 nanoparticles shows a stable capacity over 13 cycles. The absorption kinetics are unchanged though the desorption kinetics are slower on cycling.

Influence of surface chemistry on the adsorption of oxygenated hydrocarbons on activated carbons.

The objective of this work was to study the adsorption of different oxygenated hydrocarbons (methanol, ethanol, 1 and 2-butanol, methyl acetate) on activated carbons from organic mixtures with cyclohexane. Three activated carbons prepared by thermal and chemical treatments of a commercial carbon were employed for this purpose. Their textural properties were found to be similar, whereas their surface chemistries were modified, as shown by temperature-programmed desorption coupled to mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms were obtained by depletion method, and the analysis of adsorbed species was evaluated by TPD-MS to obtain new insight into the interactions between the different hydrocarbons and the carbon surface. Ethanol leads to a high-energy interaction between its hydroxyl function and the oxygenated surface groups and also to a lower energy interaction between the aliphatic part of the molecule and the carbon material. The desorption activation energy for this hydrophilic interaction is high (50 to 105 kJ/mol), and it is related to the nature of the carbon surface groups. The relative importance of these two interactions depend on the size of the alcohol/methanol is similar to ethanol, whereas butanols lead to more dispersive interactions. Methyl-acetate cannot undergo this kind of strong interaction and behaves like cyclohexane, having desorption activation energies ranging between 25 and 45 kJ/mol no matter the molecule and the carbon surface chemistry.

Size-dependent hydrogen sorption in ultrasmall Pd clusters embedded in a mesoporous carbon template.

Hydrogen sorption properties of ultrasmall Pd nanoparticles (2.5 nm) embedded in a mesoporous carbon template have been determined and compared to those of the bulk system. Downsizing the Pd particle size introduces significant modifications of the hydrogen sorption properties. The total amount of stored hydrogen is decreased compared to bulk Pd. The hydrogenation of Pd nanoparticles induces a phase transformation from fcc to icosahedral structure, as proven by in situ XRD and EXAFS measurements. This phase transition is not encountered in bulk because the 5-fold symmetry is nontranslational. The kinetics of desorption from hydrogenated Pd nanoparticles is faster than that of bulk, as demonstrated by TDS investigations. Moreover, the presence of Pd nanoparticles embedded in CT strongly affects the desorption from physisorbed hydrogen, which occurs at higher temperature in the hybrid material compared to the pristine carbon template.

Carbon and SiC macroscopic beads from ion-exchange resin templates.

A method for preparing carbon and SiC macroscopic beads using ion-exchange resins as a macrotemplate that determines the macroshape and the pore structure of the product materials is reported. First, silicates are ion-exchanged into the resins to prevent the resin from collapsing during subsequent carbonization and allow them to be used as precursors for SiC formation. SiC is prepared via carbothermal reduction of carbon/silica composite beads obtained upon carbonization of the resin/silicate in an inert atmosphere. Finally, silica is removed by HF etching. Very high-surface area (1670-2026 m2 g-1) micro- or micro-/mesoporous carbon beads and relatively high-surface area (35-63 m2 g-1) macro- and meso-/macroporous SiC beads were prepared by the described method. The pore structure and the macroshape of the particles were controlled by the type of ion-exchange resins employed, gel or macroreticular.