NUCLEATION AND GROWTH BEHAVIOR OF TELLURITE-BASED GLASSES SUITABLE FOR MID-INFRARED APPLICATIONS

Optical fibers transmitting in the 2-5 μm mid-infrared (MIR) spectral region are highly desirable for a variety of military and civilian applications including super-continuum generation, infrared countermeasures (IRCM), and MIR laser sources. These new applications in the mid-infrared require novel optical materials that transmit in this window and can be fabricated into fiber. As tellurite glasses are known to have good transparency in the (NIR) region, tellurite-based glasses are the material of choice for this study due to their high linear and nonlinear refractive index, their low glass transition temperature and the ability to form them into optical fiber. This dissertation summarizes findings on tellurite-based glasses with the composition (90-x)TeO2-10Bi2O3-xZnO with x = 15, 17.5, 20 and 25 that were processed and characterized for their potential application as novel optical fibers. Different techniques were deployed for characterization purposes, which include primarily linear refractive index measurements, structural characterization using Raman spectroscopy, and nucleation and growth behaviors, among others. The viscosity of the glasses was measured using a beam bending and parallel plate viscometers. The kinetics of crystallization of the bulk glasses and fiber with x =20 were studied using a differential scanning analyzer (DTA), a hot stage XRD and an optical microscope. The influence of compositional variation on the physical, thermal and optical properties of the glasses in the TeO2-Bi2O3-ZnO family was established. The parameters such as the thermal properties, activation energy for crystallization, Johnson-Mehl-Avrami exponent, or nucleation and growth domains and rates were determined and were found to depend on the glass composition. We correlated the composition-dependent variation of these parameters to the structure of the glasses via Raman spectroscopy. Key physical, thermal, structural and optical differences were observed and quantified between bulk glasses and their corresponding core and core-clad fibers. Also reported are the processing and characterization of modified tellurite-based glass in the TeO2-Bi2O3-ZnO glass family and efforts to reduce their absorption loss due to residual hydroxyl (OH) content. We discuss the impact of this OH reduction in the tellurite network on the physical, thermal and structural properties as well as nucleation and growth behavior of bulk glass and fiber

Glass and Glass-Ceramic Scaffolds: Manufacturing Methods and the Impact of Crystallization on In-Vitro Dissolution

Synthetic biomaterials mimicking bone morphology have expanded at a tremendous rate. Among all, one stands out: bioactive glass. Bioactive glasses opened the door to a new genre of research into materials able to promote the regeneration of functioning bone tissue. However, despite their ability to promote cell attachment, proliferation and differentiation, these materials are mainly used as granules. However to promote loaded and sustained bone repair, a 3D structure, with open and highly interconnected pores, is desirable. 3D scaffolds are generally produced into green bodies via various techniques. The particles are then bound together via sintering. However, the highly disrupted silica network of the typical bioactive glasses composition leads to crystallization. Therefore, sintering of the most commonly used bioactive glass compositions (i.e. 45S5 and S53P4) leads to partly to fully crystallize bodies. The impact of crystallization on bioactivity still leads to large debate among the scientific community. Does crystallization reduce or suppress the materials bioactivity? Within this chapter, the processing routes for scaffold manufacture are presented, as well as an introduction to the thermal processing of glasses to form glass and glass-ceramics and the consequent effect on bioactivity is discussed

In vitro cytocompatibility of antibacterial silver and copper-doped bioactive glasses

Fighting the formation of bacterial biofilm and simultaneously providing a bioactive environment for bone regeneration during the treatment of orthopedic infections is one of the greatest challenges in surgery. Moreover, the major global threat of rapidly increasing antimicrobial resistance calls for non-antibiotic alternatives. Bioactive glasses doped with antibacterial metal ions silver (Ag), or copper (Cu), offer a potential solution. However, an added challenge is the cytocompatibility of these antimicrobial biomaterials, which could be compromised due to the possible cytotoxic effect of the dopants. This work evaluates the cytocompatibility of two bioactive glasses, SBA2 and SBA3, either doped with Ag- (Ag-SBA2) or Cu-ions (Cu-SBA3) via ion-exchange process. The viability, proliferation, and morphology of human adipose stem cells (hASCs) were evaluated using different culture conditions: i) direct culture on glass discs, with and without pre-incubation, and ii) in medium containing glass dissolution byproducts. The release kinetics of the doped ions was evaluated in α-MEM and during cell culture. Moreover, the effect of protein adsorption on the cell response was studied by introducing a layer of fibronectin on the glass discs before direct culture with hASCs. Ag-SBA2 and Cu-SBA3 both initially inhibited the hASC viability in direct cell culture. However, cells remain viable with healthy morphology when cultured directly on pre-treated discs, or indirectly with the glass dissolution byproducts. This suggests that the cytotoxicity effect seems to arise from the contact toxicity between the cells and the material surface. Fibronectin adsorption significantly improved the cytocompatibility of Ag-SBA2, while Cu-SBA3 requires further optimization. To conclude, Ag-SBA2, through its contact toxicity, has the potential for treating early infection, without compromising long-term cytocompatibility and bioactivity. However, further optimization of the Cu-SBA3 glass is needed due to its cytotoxicity towards hASCs.Peer reviewe

Effect of the addition of Al2O3, TiO2 and ZnO on the thermal, structural and luminescence properties of Er3+-doped phosphate glasses

Er-doped phosphate glasses were fabricated by melt-quenching technique. The changes in their thermal, structural and luminescence properties with the addition of Al2O3, TiO2 or ZnO were studied. Physical and thermal properties were investigated through density measurement and differential thermal analysis. Structural characterization was performed using the Raman and Infrared spectroscopy. In order to study the influence of the composition on the luminescence properties of the glasses, the refractive index, the luminescence spectra and the lifetime values were measured. The results show that with the addition of Al2O3 and TiO2 the phosphate network becomes more connected increasing the glass transition temperature, whereas the addition of ZnO does not show significant changes in the optical, thermal and structural properties but it leads to a larger emission cross-section at 1540 nm as compared to the other glasses. As the site of the Er3+ is not strongly affected by the change in the glass composition, we think that the emission properties of the glasses depend on the glass structure connectivity, which has an impact on the Er3+ ions solubility.Comment: 32 pages, 9 figures, 1 tabl

Functionalization of a chemically treated Ti6Al4V-ELI alloy with nisin for antibacterial purposes

This research aims to define a protocol for nisin adsorption onto Ti6Al4V- Extra Low Interstitial content (ELI) alloy to reduce the risk of peri-implant infections. The substrate is, first, etched to get a nanotextured surface with a high density of acidic hydroxyl groups and then functionalized with the antimicrobial peptide nisin. Nisin adsorption is performed at different pH values, in the range of 5–7. The nisin release in inorganic solutions mimicking physiological or pro-inflammatory conditions is tested. The surfaces are characterized by profilometry, SEM/EDS, contact angle and surface free energy measurements, zeta potential titrations, DLS, XPS, and UV–visible spectroscopy. Effective surface adsorption was achieved and maximized at pH 6. The coated surface has high surface energy suitable for tissue integration and it releases nisin in a time longer than 1 day. As a confirmation of the antibacterial properties due to the nisin adsorption, specimens were incubated with Staphylococcus aureus, whose metabolic activity was reduced by ≈ 70% in comparison to the untreated control, and the number of viable adhered colonies was ≈ 6 times reduced. In conclusion, coupling of nisin to a chemically treated titanium surface is promising for a bioactive and antibacterial surface for tissue integration

Bioactive glass–ceramics containing fluorapatite, xonotlite, cuspidine and wollastonite form apatite faster than their corresponding glasses

Crystallisation of bioactive glasses has been claimed to negatively affect the ion release from bioactive glasses. Here, we compare ion release and mineralisation in Tris–HCl buffer solution for a series of glass–ceramics and their parent glasses in the system SiO2–CaO–P2O5–CaF2. Time-resolved X-ray diffraction analysis of glass–ceramic degradation, including quantification of crystal fractions by full pattern refinement, show that the glass–ceramics precipitated apatite faster than the corresponding glasses, in agreement with faster ion release from the glass–ceramics. Imaging by transmission electron microscopy and X-ray nano-computed tomography suggest that this accelerated degradation may be caused by the presence of nano-sized channels along the internal crystal/glassy matrix interfaces. In addition, the presence of crystalline fluorapatite in the glass–ceramics facilitated apatite nucleation and crystallisation during immersion. These results suggest that the popular view of bioactive glass crystallisation being a disadvantage for degradation, apatite formation and, subsequently, bioactivity may depend on the actual system study and, thus, has to be reconsidered

Mechanical Properties of Robocast Glass Scaffolds Assessed through Micro-CT-Based Finite Element Models

In this study, the mechanical properties of two classes of robocast glass scaffolds are obtained through Computed micro-Tomography (micro-CT) based Finite Element Modeling (FEM) with the specific purpose to explicitly account for the geometrical defects introduced during manufacturing. Both classes demonstrate a fiber distribution along two perpendicular directions on parallel layers with a (Formula presented.) tilting between two adjacent layers. The crack pattern identified upon compression loading is consistent with that found in experimental studies available in literature. The finite element models have demonstrated that the effect of imperfections on elastic and strength properties may be substantial, depending on the specific type of defect identified in the scaffolds. In particular, micro-porosity, fiber length interruption and fiber detaching were found as key factors. The micro-pores act as stress concentrators promoting fracture initiation and propagation, while fiber detachment reduces the scaffold properties substantially along the direction perpendicular to the fiber plane.publishedVersionPeer reviewe

Novel borosilicate bioactive scaffolds with persistent luminescence

Persistent luminescent amorphous borosilicate scaffolds were successfully prepared, for the first time, with a porosity of >70% using the burn-off technique. The persistent luminescence was obtained by adding the SrAl2O4:Eu2+,Dy3+ microparticles: i) in the glass melt or ii) in the glass crushed into powder prior to the sintering. The scaffolds prepared by adding the microparticles in the glass melt exhibits lower persistent luminescence and a slower reaction rate in simulated body fluid than the scaffolds prepared by adding the microparticles in the glass powder due to the release of strontium from the microparticles into the glass during the glass melting.</p