Bioactive glasses synthesized by the sol-gel technique possess many of the qualities associated with an ideal scaffold material for a bone graft substitute. In view of the potential clinical applications, we performed a detailed in vitro study of the biological reactivity of synthesized 58S bioactive glass containing-zinc, in terms of osteoblast morphology, proliferation, and deposition of a mineralized extracellular matrix (ECM). Human Sarcoma Osteoblast (SAOS-2) cells were used to i) assess cytotoxicity by lactate dehydrogenase (LDH) release and ii) evaluate the deposition of a calcified extracellular matrix by ELISA assay and quantitative RT-PCR (qRT-PCR). In comparison with pure silica and 58S, the 58S-Zn0.4 bioglass showed a significant increase in cellular proliferation and deposition of ECM components such as decorin, fibronectin, osteocalcin, osteonectin, osteopontin, type-I and -III collagens. Calcium deposition was significantly higher than on pure silica and 58S samples. Also Alkaline phosphatase (ALP) activity and its protein content was higher with respect to pure silica and 58S. qRT-PCR analysis revealed the up-regulation of type-I collagen, bone sialoprotein and osteopontin genes. All together these results demonstrate the cytocompatibility of 58S-Zn0.4 bioglass and its capability to promote osteoblast differentiation.

We report experimental results on the time decay of photoluminescence at 4.2 eV in Ge-doped silica. This optical emission is assigned to a singlet-singlet transition between electronic states localized on an oxygen deficiency nearby a Ge atom and its radiative decay rate is in competition with an intersystem crossing mechanism that populates an excited triplet state. We investigate the dependence of the lifetime of this photoluminescence on the temperature, in the 6 -295 K range, and on the excitation energy, in the ultraviolet and vacuum ultraviolet region. The mean value of the decay time decreases on increasing the temperature, in agreement with the phonon-assisted nature of the intersystem crossing process whose activation energy is estimated ϳ90 meV. In particular, at temperatures higher than 145 K, the time decay of the 4.2 eV emission deviates from a single exponential law and depends on the excitation energy, suggesting the presence of a distribution of intersystem crossing rates. These features are ascribed to the structural heterogeneity of vitreous matrix embedding the optical active point defects.

Acid-doped polybenzimidazole (PBI) membranes are considered as one of the most attractive alternatives to Nafion in polymer fuel cells (PEMFCs). [1][2][3] At present, however, their use at temperatures below $160 8C is impeded by the leaching of the free phosphoric acid from the membrane in presence of liquid water, which causes a drop in conductivity of many orders of magnitude during fuel cell operation. To overcome this problem, we investigated the suitability of silica derivatized with imidazole-based functionalities as fillers able to improve the acid retention capability of the membrane. We show that even small amounts ($10 wt %) of filler increase the permanent proton conductivity of the PBI composite membranes by a factor >10 3 in comparison with that of unfilled PBI. The preparation of PBI composite membranes with basic functionalities is a promising way to make possible their use in PEMFCs operating around 120 8C, that is, the temperature required for automotive applications. During the last ten years, polybenzimidazole-based separators have been widely investigated for what concerns polymer synthesis and casting process, [4] membrane thermal stability, [5]

This project used retinal pigment epithelial (RPE) cells to investigate the effects of up- and down-regulation of cathepsin D expression on the processing of cathepsin D and on the normal phagocytic and digestive function of these cells. RPE cells were transfected with a pHbetaApr-1-neo vector construct carrying the full-length sequence of the translated region of human cathepsin D in sense and antisense directions. Transfected cells were characterized for the presence and expression of the transgene by PCR amplification using transgene-specific primers. Total aspartic proteinase activity present in transformed RPE cells was measured by an enzyme assay using haemoglobin as substrate. Flow cytometry was used to quantify phagocytosis of fluorescein isothiocyanate-labelled rod outer segments (ROS), and lysosomal digestion of ROS was monitored by immunofluorescence. A 435 bp fragment was present in RPE cells carrying the cathepsin D transgene in sense and antisense orientations after PCR amplification. Expression of both 52 kDa procathepsin D and 34 kDa active cathepsin D was significantly up-regulated in sense cathepsin D-transfected RPE cells and down-regulated in RPE cells transfected with antisense cathepsin D. No other forms of cathepsin D were detected in the transfected cells, suggesting that, if pseudo-cathepsin D exists in RPE cells in vivo, it requires the presence of unknown specific regulatory elements. The up- and down-regulation of cathepsin D expression was further confirmed by enzyme assay. Transfected cells retained their phagocytosing ability after ROS challenge and maintained their ability to process ROS. The processing of ROS was significantly slower in RPE cells transfected with antisense than control vector or in sense-cathepsin D-transfected cells. These results demonstrate that cathepsin D is a major proteolytic enzyme participating in the lysosomal digestion of photoreceptor outer segments.

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Bioactive glasses and glass-ceramics of the system SiO 2 -P 2 O 5 -CaO with and without zinc were synthesized by sol-gel with the aim to address the influence of both the chemical composition and the microstructure on the growth of hydroxycarbonate apatite (HCA) following soaking in simulated body fluid (SBF). In the standard compositions 58S, 70S, and 80S the silica precursor was also partially replaced with a nanoscale silica powder (HiSil) in order to separate the contributions of porosity and composition. The combined use of XRPD, N 2 absorption measurements, and SEM allowed us to establish quantitative correlations among the above-mentioned quantities. We found that the HCA formation rate increases with the silica content and that an important role is played by the specific surface area of the samples. Notably, the addition of even small quantities (0.4 wt %) of ZnO at the expenses of both CaO and P 2 O 5 in the 58S glass leads to the increase, with respect to the 58S sample, of both the HCA formation rate and the HCA content after 8 days of treatment in SBF. A preliminary result revealed that sample with 0.4 wt % ZnO displayed good in vitro biocompatibility as shown by LDH assay.

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