Design and Performance of an Adsorption Bed with Activated Carbons for Biogas Purification.

Organic waste can be efficiently converted into energy using highly efficient energy systems, such as SOFCs coupled to the anaerobic digestion process. SOFC systems fed by biogenous fuels, such as biogas or syngas, suffer long-term stability due to trace compound impacts. It follows that, a mandatory gas cleaning section is needed to remove these pollutants at lower concentrations. This work investigates the adsorption mechanism for micro-contaminant removal through experimental results achieved using solid sorbents. Samples of different sorbent materials were analyzed in the laboratory to determine their performances in terms of sulfur (mainly hydrogen sulfide) and siloxanes (mainly D4-Octamethylcyclotetrasiloxane) adsorption capacities. The analysis shows that the chemical composition of the samples influences the adsorption of H2S (i.e., presence of calcium, iron, copper), while the effect of their textural properties mainly influences the adsorption of siloxane compounds, such as D4. A quantitative analysis was performed considering the influence of gas velocity on adsorption capacity. By increasing the biogas velocity (+45% and +89%), there was an indirect correlation with the H2S adsorption capacity (-27% and -44%). This identified an aspect related to the residence time required to be able to remove and retain the trace compound. The results obtained and summarized were used to develop a strategy for the removal of trace compounds in large-scale plants, e.g., for water purification.

Biomimetic and mesoporous nano-hydroxyapatite for bone tissue application: a short review.

In the last decades, many research groups have experimented the synthesis of hydroxyapatite (HA) for bone tissue application obtaining products with different shapes and dimensions. This review aims to summarise and critically analyse the most used methods to prepare physiologic-like nano-HA, in the form of plates or rods, similar to the HA present in the human bones. Moreover, mesoporous HA has gained increasing interest in the biomedical field due its pecualiar structural features, such as high surface area and accessible mesoporous volume, which is known to confer enhanced biological behaviour and the possibility to act as nanocarriers of functional agents for bone-related therapies. For this reason, more recent studies related to the synthesis of mesoporous HA, with physiological-like morphology, are also considered in this review. Since a wide class of surfactant molecules plays an essential role both in the shape and size control of HA crystals and in the formation of mesoporosity, a section devoted to the mechanisms of action of several surfactants is also provided.

Osteoporosis-related variations of trabecular bone properties of proximal human humeral heads at different scale lengths.

Osteoporosis (OP) is a skeletal disorder responsible for the weakening of the bone structure and, consequently, for an increased fracture risk in the elderly population. In the past, bone mineral density (BMD) variation was considered the best OP indicator, but recently the focus has shifted toward the variation of microstructural bone parameters. This work is based on the characterisation of 8-mm cylindrical biopsies harvested from proximal humeral heads belonging to healthy and osteoporotic patients, in order to assess the OP-related variations of bone properties at different scale lengths. In particular, bone biopsies underwent micro-computed tomography analysis to study the most relevant features of bone architecture and extrapolate the tissue mineral density (TMD) value of bone trabeculae. Compression tests and nanoindentations were performed to investigate the macro- and micromechanical properties of bone biopsies, respectively. In addition, XRD analyses were performed to obtain the mean hydroxyapatite (HA) crystallite size, while Raman spectroscopy investigated the collagen secondary structure. Thermogravimetric analysis was performed to evaluate the ratio between organic and inorganic phases. From the obtained results, OP samples showed a more anisotropic and less interconnected structure responsible for reduced compression strength. From this, it can be supposed that OP caused an alteration of bone structure that led to inferior macroscopic mechanical properties. Furthermore, OP samples possessed higher TMD and bigger HA crystals that are correlated to an increase of the hardness value obtained by means of nanoindentation. This less controlled HA crystal growth is probably due to an alteration of the organic matrix structure, as revealed by the increase of the random coil contribution in the Raman spectra of the OP bone. This higher crystal content led to an increase in trabecular density and hardness. In conclusion, the obtained data showed that OP affects bone properties at different scale lengths causing an alteration of its morphological, structural and mechanical features.

The Incorporation of Strontium to Improve Bone-Regeneration Ability of Mesoporous Bioactive Glasses.

Over the recent years, mesoporous bioactive glasses (MBGs) gained interest as bone regeneration systems, due to their excellent bioactivity and ability to release therapeutic molecules. In order to improve the bone regeneration ability of MBGs, the incorporation of Sr2+ ions, due to its recognized pro-osteogenenic potential, represents a very promising strategy. In this study, MBGs based on the SiO2⁻CaO system and containing different percentages (2 and 4 mol %) of strontium were prepared by two synthesis methods, in the form of microspheres and nanoparticles. Sr-containing MBGs were characterized by FE-SEM, XRD and N2 adsorption/desorption analysis. The in vitro bioactivity in SBF resulted excellent. The assessment of fibroblast cell (line L929) viability showed that Sr-containing MBGs were biocompatible both in form of micro- and nanoparticles. The osteogenic response of osteoblast-like SAOS-2 cells was investigated by analysing the expression of GAPDH, COL1a1, RANKL, SPARC, OPG and ALPL genes, as cell differentiation markers. The results indicate that the incorporation of Sr into MBG is beneficial for bone regeneration as promotes a pro-osteogenic effect, paving the way to the design of advanced devices enabled by these nanocarriers also in combination with drug release, for the treatment of bone pathologies, particularly in patients with osteoporosis.

Bioactive Glass-Ceramic Foam Scaffolds from 'Inorganic Gel Casting' and Sinter-Crystallization.

Highly porous bioactive glass-ceramic scaffolds were effectively fabricated by an inorganic gel casting technique, based on alkali activation and gelification, followed by viscous flow sintering. Glass powders, already known to yield a bioactive sintered glass-ceramic (CEL2) were dispersed in an alkaline solution, with partial dissolution of glass powders. The obtained glass suspensions underwent progressive hardening, by curing at low temperature (40 °C), owing to the formation of a C-S-H (calcium silicate hydrate) gel. As successful direct foaming was achieved by vigorous mechanical stirring of gelified suspensions, comprising also a surfactant. The developed cellular structures were later heat-treated at 900-1000 °C, to form CEL2 glass-ceramic foams, featuring an abundant total porosity (from 60% to 80%) and well-interconnected macro- and micro-sized cells. The developed foams possessed a compressive strength from 2.5 to 5 MPa, which is in the range of human trabecular bone strength. Therefore, CEL2 glass-ceramics can be proposed for bone substitutions.