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The aim of this paper was to synthesize and characterize polymeric scaffolds of Chitosan/Xanthan/Hydroxyapatite-Graphene Oxide nanocomposite associated with mesenchymal stem cells for regenerative dentistry application. The chitosan-xanthan gum (CX) complex was associated with Hydroxyapatite-Graphene Oxide (HA-GO) nanocomposite with different Graphene Oxides (GO) concentration (0.5 wt%; 1.0 wt%; 1.5 wt%). The scaffolds characterizations were performed by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and contact angle. The mechanical properties were assessed by compressive strength. The in vitro bioactivity and the in vitro cytotoxicity test (MTT test) were analyzed as well. The data was submitted to the Normality and Homogeneity tests. In vitro Indirect Cytotoxicity assay data was statistically analyzed by ANOVA two-way, followed by Tukey’s test (α = 0.05). Compressive strength and contact angle data were statistically analyzed by one-way ANOVA, followed by Tukey’s test (α = 0.05). XRD showed the presence of Hydroxyapatite (HA) peaks in the structures CXHA, CXHAGO 0.5%,1.0% and 1.5%. FT-IR showed amino and carboxylic bands characteristic of CX. Raman spectroscopy analysis evidenced a high quality of the GO. In the TGA it was observed the mass loss associated with the CX degradation by depolymerization. SEM analysis showed pores in the scaffolds, in addition to HA incorporated and adhered to the polymer. Contact angle test showed that scaffolds have a hydrophilic characteristic, with the CX group the highest contact angle and CXHA the lowest ( p < 0.05). 1.0 wt% GO significantly increased the compressive strength compared to other compositions. In the bioactivity test, the apatite crystals precipitation on the scaffold surface was observed. MTT test showed high cell viability in CXHAGO 1.0% and CXHAGO 1.5% scaffold. CXHAGO scaffolds are promising for regenerative dentistry application because they have morphological characteristics, mechanical and biological properties favorable for the regeneration process.

Multiphasic calcium phosphate powders were synthesized by the acidic route, using lactic acid as a chelating agent that allows the production of a stable and rich solution of calcium and phosphate ions at room temperature. After pH adjusting, without varying the concentrations of precursor solution, XRD and FTIR analyses showed different CaP phases before and after heat treatment at 1000 °C. At pH 5, brushite plate-like particles were produced, while at higher pH levels (7 to 12) nano-hydroxyapatite particles were formed. After the calcination process, partial and total decomposition of hydroxyapatite in the β-TCP phase was explained by XRF analysis due to the calcium-deficient hydroxyapatite of synthesized samples at pH 7 and 10. This work presents an important method to synthesize any desired CaP phase compositions by varying the pH level and subsequently performing heat treatment, which has a direct effect on morphology, crystallinity, and formation of different CaP powders.

Resumo Este trabalho objetivou produzir nanocompósitos de hidroxiapatita (HA) com óxido de grafeno (GO), a fim de investigar a interação entre tais materiais. Os nanocompósitos de hidroxiapatita-grafeno foram produzidos com adição de 0,5%, 1,0% e 1,5% em peso de GO à HA. Para avaliar a interação físico-química entre as superfícies destes materiais, foram realizadas análises de espectroscopia Raman e espectroscopia no infravermelho por transformada de Fourier (FTIR). A análise por Raman indicou que a adição de GO não afetou a banda característica da HA, sendo observadas as bandas D e G do óxido de grafeno. Além disso, o aumento da adição de GO levou a uma variação das intensidades das bandas D e G e nos valores de deslocamento no espectro Raman. Estes resultados sugerem uma possível transformação estrutural da HA-GO. Os resultados de FTIR indicaram que o aumento da adição do GO levou à ampliação da banda associada à água adsorvida, dada a natureza higroscópica do óxido de grafeno. A ausência da banda relacionada ao grupo carbonila do GO indicou a influência das nanopartículas de HA em sua superfície. Palavras-chave: Hidroxiapatita; Grafeno; Óxido de grafeno; Nanocompósitos.

A collection of Al-SBA-15 mesoporous catalysts (Si/Al = 13–174) was investigated to overcome typical accessibility constraints of microporous solids. 27Al MAS NMR confirmed the existence of tetrahedrally coordinated Al in the catalyst’s framework, and the fraction of such species increased as the Si/Al ratio decreased. Brønsted acidity followed the same pattern found using n-propylamine thermodecomposition. Mesoporous catalysts with lower Si/Al ratios exhibited a higher affinity to water as quantitatively determined using water adsorption experiments. Those surface properties were correlated to the catalytic performance on oleic acid esterification. The introduction of Al into the SBA-15 framework significantly improved esterification activity, leading to conversions ranging from 70 to 93%. This was explained by the acidity engendered upon Si substitution by Al. However, a turning point from which activity started dropping was registered and it was proposed to be associated with catalyst hydrophilicity. The balance between acidity and hydrophilicity was unveiled to be of paramount importance to accomplish the best catalytic efficiency and uppermost biofuel yield. Catalyst activity was also assessed for the esterification of stearic and linoleic acids. Higher conversion rates were accomplished with unsaturated fatty acids (oleic acid > linoleic acid > stearic acid) due to the higher reactivity of the carboxylic acid moieties as a consequence of the polarity of the double bonds in the carbon chain.

Resumo Este trabalho teve como objetivo produzir óxido de grafeno (GO) pelo método de Hummers modificado, controlando o tamanho das folhas de GO pelo processo de ultrassom. O processo foi executado utilizando um banho ultrassônico com o tempo determinado de 2 e 6 horas. Para caracterização física e avaliação morfológica das folhas de GO produzidas, foram realizadas análises espectroscopia Raman e microscopia eletrônica de varredura (MEV), respectivamente.