|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Sintesi, caratterizzazione e valutazione della attività enzyme-like di vetri potenzialmente bioattivi contenenti Ce3+/Ce4+|
|Titolo in inglese||Ce3+/Ce4+-containing potential bioactive glasses: synthesis, characterization, and evaluation of enzyme-like activity|
|Settore scientifico disciplinare||CHIM/03 - CHIMICA GENERALE E INORGANICA|
|Corso di studi||MODELS AND METHODS FOR MATERIAL AND ENVIRONMENTAL SCIENCES|
|Data inizio appello||2017-04-06|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
In questo lavoro di tesi sono stati sintetizzati per fusione vetri bioattivi drogati con ossido di cerio, i vetri sono stati poi testati per verificare se sono in grado di agire come antiossidanti al pari delle nanoparticelle di ceria. I risultati ottenuti dall’immersione dei vari campioni in soluzioni di acqua ossigenata a concentrazioni diverse per tempi crescenti ha dimostrato che i vetri testati sono efficaci nell’aumentare la degradazione di H2O2, mimando l’attività dell’enzima catalase, che degrada H2O2 in H2O e O2.
Ce-containing bioactive glasses synthesized via melting were tested to verify if they are able to act as antioxidant as nanoceria does. The results obtained from the immersion of the samples in different H2O2 solutions for increasing times demonstrate that the tested glasses are successful in increasing the rate of decomposition of H2O2, mimicking the activity of the enzyme catalase, that degrades H2O2 into H2O and O2. At first, we doped and tested a phospho-silicate glass with a starting composition that is well known to be bioactive: the 45S5 Bioglass®. The catalase mimic activity tests revealed that the antioxidant properties of the Ce-containing glasses are related to the concentration of CeO2; in addition, during the tests in H2O2+SBF we noticed that when the soaking was performed in a PO43- rich environment the degradation rate slows down. Since the CeONPs show the same problem when placed in a phosphate environment, we wondered if even the PO43- present in the glass matrix could affect the catalytic response of the glasses. To verify this hypothesis, a PO43--free composition was doped with cerium and tested for catalase mimic activity. The results highlight that the phosphate-free glasses causes a better response, thus the enzyme-like activity of the glasses depends from both the content of cerium and the chemical composition of the starting glass. Unluckily, the Ce-doped glasses obtained by melting showed a low bioactivity in terms of hydroxyl-apatite formation during bioactivity tests in SBF. Mesoporous bioactive glasses (MBG) synthesized via sol-gel & EISA process show a greater bioactivity compared to the melted glasses. Thus, we synthesized MBG samples doped with cerium. The aim was to obtain a glass with antioxidant properties, able to retain the bioactivity even when doped. The MBG_5.3 glass appeared to be the most satisfying sample. In seven days, it is able to disrupt a large amount of hydrogen peroxide, and IR and XRD analyses performed after bioactivity tests show presence of hydroxyl-apatite on the surface of the sample after two weeks. After the confirmation that the synthesized glasses are able to act as catalase mimic materials, and that this ability is dependent on the kind of glass, and on the content of cerium, we wonder if they are able to mimic also the activity of the superoxide dismutase (SOD), that is to degrade superoxide into oxygen and hydrogen peroxide. The SOD mimic activity tests confirm that the synthesized samples are able to act also as SOD mimic material. We performed the XPS analysis over the tested glasses before and after treatment in H2O2 to verify if there is a change in the Ce3+/Ce4+ ratio, and if this change affects the enzyme-like behaviour of the glasses. The analysis show that the degradation is higher when the ratio Ce3+/Ce4+ has a certain value that depends on the soaking solution. This behaviour is consistent with the one of the CeONPs, in particular glasses with low Ce3+/Ce4+ ratio show high catalase mimetic activity. Finally, we started to perform the cytocompatibility tests on pre-osteoblastic MC3T3-E1 cells. The preliminary data collected highlight that the cerium in the glasses appears to be helpful for the cells: the viability of the cells in contact with the doped glasses is higher than the viability of the cells in contact with the undoped ones. The results collected are satisfactory and encourage continuing the study on the systems presented above.