Hugo R. Fernandes

Production and characterisation of glass ceramic foams from recycled raw materials

Abstract Glass foams were produced exclusively from industrial residues, namely from sheet glass cullet and fly ashes from thermal power plant as the main components, and from burned wastes of silicon carbide (SiC) abrasive papers. The experimental results showed that homogenous microstructures of large pores could be obtained by adding an optimum amount (1 wt-%) of a commercial SiC powder (SiCC) after sintering at 950°C. The SiCC was then replaced by equivalent amounts of SiC abrasive paper ashes of different grain sizes. The SiC containing foams led to apparent density and compressive strength values of about 0⋅18–0⋅35 g cm–3 and 0⋅9–1⋅8 MPa. Good correlations between compressive strength, apparent density and microstructure (pore size, strut thickness and internal porosity) were observed.

Bioglass implant-coating interactions in synthetic physiological fluids with varying degrees of biomimicry

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid–implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials’ structure-dissolution behavior. This will contribute to “upgrade” our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic–organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials.

Glass structure and crystallization of Al and B containing glasses belonging to the Li2O–SiO2 system

The aim of the present work is to investigate the effect of substituting B2O3 for Al2O3 in a non-stoichiometric lithium disilicate (Li2Si2O5, LS2) glass composition belonging to the system Li2O–K2O–Al2O3–SiO2. Addition of equimolar amounts of K2O and Al2O3 to binary lithium silicate glass compositions improves chemical resistance, sintering behaviour and mechanical properties of the glass-ceramics produced from sintered glass powder compacts. However, in bulk (monolithic) glasses Al2O3 addition hinders bulk nucleation. It also suppresses crystallization of LS2 and promotes formation of a meta-stable crystalline phase called lithium metasilicate (Li2SiO3, LS). The results showed that B substitution resulted in the depolymerisation of the glass network increasing the percentage of NBOs leading to decreasing viscosity, molar volumes, oxygen densities and glass transition temperatures. The simultaneous addition of Al and B into the glass composition resulted in decreased liquid–liquid phase segregation (LLPS) and lower crystal nucleation tendency when compared to Al pure or B pure compositions. Further, Al rich glasses featured lithium metasilicate crystallization at initial stages and then transformed into LS2 at higher temperatures, while with B addition glasses crystallize directly into LS2.

Role of manganese on the structure, crystallization and sintering of non-stoichiometric lithium disilicate glasses

The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O–K2O–Al2O3–SiO2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength (Δo) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts.

Preparation of Mullite Whiskers from Kaolinite Using CuSO4 as Fluxing Agent

Mullite whiskers were produced by firing of kaolin at 1400o-1550oC. CuSO4 was used as fluxing agent. Before firing, spray drying and baking with flour and leaven were employed to give free space to the powders. The influence of preparation parameters and firing temperature on the crystalline structure and phase transformations during the entire process was determined. The results showed that there was a beneficial effect of both the incorporation of CuSO4 and the given free space on the formation of mullite whiskers. There was no evidence for the effect of firing temperature on the aspect ratio and morphology of the whiskers within the investigated range.

Synthesis and bioactivity assessment of high silica content quaternary glasses with Ca:P ratios of 1.5 and 1.67, made by a rapid sol-gel process

Sol-gel glasses in quaternary silica-sodium-calcium-phosphorous systems have been synthesized using a rotary evaporator for rapid drying without ageing. This novel fast drying method drastically decreases the total drying and ageing time from several weeks to only 1 hour, thus overcoming a serious drawback in sol-gel preparation procedures for bioglasses. This work investigates the bioactivity behavior of two glasses synthesized by this fast method, with Ca:P ratios of 1.5, and 1.67. X-ray diffraction (XRD), Inductive coupled plasma, Fourier-transform infrared, and Raman spectroscopy were used to confirm the bioactivity of the synthesized powders. MAS-NMR was also used to assess the degree of silica polymerization. The composition with a higher Ca:P = 1.67 ratio showed better bioactivity in comparison to the one with Ca:P = 1.5, which exhibited little bio-response with up to 4 weeks of immersion in SBF (simulated body fluid). It was also found that an orbital agitation rate of 120 rpm favors the interfacial bio-mineralization reactions, promoting the formation of a crystalline hydroxyapatite (HAp) layer at the surface of the (Ca:P = 1.67) composition after 2 weeks immersion in SBF.

Osteogenic capacity of alkali‐free bioactive glasses. In vitro studies

The high alkali content bioactive glasses commonly used to regenerate bone in dental, orthopedic, and maxillofacial surgeries induce some cytotoxicity in surrounding tissues. The present study aims the ability of some alkali-free bioactive glasses compositions, recently developed by our research group, to stimulate human mesenchymal stem cells (hMSCs) differentiation into osteoblasts in comparison to 45S5 Bioglass® . The obtained results demonstrated that alkali-free bioactive glasses possess higher stimulating towards differentiation of hMSCs in comparison to the control 45S5 Bioglass® . The von Kossa assay demonstrated that all bioactive glasses studied were able to induce the appearance of calcium deposits even when the cells were cultured in DMEM, proving that these biomaterials per se induce hMSCs cell differentiation. It was also observed that in both cell culture medium used (DMEM, and osteogenesis differentiation medium) alkali-free bioactive glasses clearly induced the appearance of more calcium deposits than the 45S5 Bioglass® , indicating their greater ability to induce cell differentiation. In summary, these results indicate that alkali-free bioactive glasses are a safe and valid alternative to 45S5 Bioglass® .

Synthesis and Characterization of Synthetic F-Mica Containing Glass-Ceramics in the System SiO 2 ·Al 2 O 3 ·B 2 O 3 ·CaO·MgO·Li 2 O·(K,Na) 2 O·F

Ions of Li, Na, K, and B were incorporated in Ca-mica, CaMg 3 Al 2 Si 2 O 1 0 F 2 . The crystallization process and the properties of the resulting glass-ceramics were experimentally determined, and the role of the anions and cations is discussed. According to the results, Li, K, and Na ions strongly affected the formation of the crystalline phases. Until 900 °C, pargasite and F-cannilloite amphiboles and KLi-mica were predominately crystallized. The two amphiboles are dissociated, yielding stable forsterite at 900 °C and Ca-mica and spinel at 950 °C. KLi-mica showed remarkable stability and growth within the investigated temperature range, until 1000 °C. The optimum crystallization temperature for the investigated glass-ceramics is between 800 °C and 900 °C. The produced glass-ceramics exhibited capability for easy bulk crystallization, high whiteness, translucency, and mechanical and chemical properties suitable for several applications.