Development of Zirconia based phosphors for application in lighting and as luminescent bioprobes

The strong progress evidenced in photonic and optoelectronic areas, accompanied by an exponential development in the nanoscience and nanotechnology, gave rise to an increasing demand for efficient luminescent materials with more and more exigent characteristics. In this field, wide band gap hosts doped with lanthanide ions represent a class of luminescent materials with a strong technological importance. Within wide band gap material, zirconia owns a combination of physical and chemical properties that potentiate it as an excellent host for the aforementioned ions, envisaging its use in different areas, including in lighting and optical sensors applications, such as pressure sensors and biosensors. Following the demand for outstanding luminescent materials, there is also a request for fast, economic and an easy scale-up process for their production. Regarding these demands, laser floating zone, solution combustion synthesis and pulsed laser ablation in liquid techniques are explored in this thesis for the production of single crystals, nanopowders and nanoparticles of lanthanides doped zirconia based hosts. Simultaneously, a detailed study of the morphological, structural and optical properties of the produced materials is made. The luminescent characteristics of zirconia and yttria stabilized zirconia (YSZ) doped with different lanthanide ions (Ce3+ (4f1), Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8), Dy3+ (4f9), Er3+ (4f11), Tm3+ (4f12), Yb3+ (4f13)) and co-doped with Er3+,Yb3+ and Tm3+,Yb3+ are analysed. Besides the Stokes luminescence, the anti- Stokes emission upon infrared excitation (upconversion and black body radiation) is also analysed and discussed. The comparison of the luminescence characteristics in materials with different dimensions allowed to analyse the effect of size in the luminescent properties of the dopant lanthanide ions. The potentialities of application of the produced luminescent materials in solid state light, biosensors and pressure sensors are explored taking into account their studied characteristics.

Coating bioattivi su zirconia per applicazioni in campo biomedicale: stato dell'arte e prospettive

I materiali bioceramici, in base alla loro capacità d’interazione con l’osso e i tessuti del corpo umano, possono essere classificati in bioinerti e bioattivi. I materiali bioinerti, una volta impiantati, formano uno strato fibroso, non aderente, all’interfaccia con l’osso. Tale strato è una forma naturale di protezione che l’organismo adotta per isolare il materiale che viene, inizialmente, percepito come estraneo. Al contrario, i materiali bioattivi, una volta impiantati, mostrano una risposta biologica immediata, creando un legame attivo con l’osso e i tessuti nel quale vengono impiantati, favorendo e velocizzando la guarigione. La zirconia è un materiale ceramico altamente biocompatibile, definito come bioinerte per la sua scarsa capacità d’integrazione con l’osso ed i tessuti dell’organismo umano. Questa sua particolarità può, nel lungo termine, comprometterne la funzione fino ad arrivare, in alcuni casi, al totale malfunzionamento dell’impianto. Negli ultimi anni, diversi studi sono stati condotti con lo scopo di aumentare la capacità di biointegrazione della zirconia ed alcuni brevetti sono stati depositati. L’obiettivo del presente lavoro è quello di condurre un’analisi bibliografica ed una ricerca brevettuale sul tema dei coating bioattivi su zirconia per impianti dentali ed ortopedici. La necessità di condurre questo studio deriva dalla crescente richiesta di utilizzo della zirconia, in particolare, nel settore dentale. La zirconia rappresenta, infatti, ad oggi, il migliore candidato per la sostituzione dei metalli negli impianti dentali. Le buone proprietà meccaniche, l’eccellente biocompatibilità e l’aspetto estetico molto simile a quello dei denti naturali, rendono questo materiale particolarmente adatto a questo genere di applicazioni. La possibilità di rendere la sua superficie bioattiva rappresenta un importante miglioramento delle prestazioni in termini di biointegrazione, durabilità, sicurezza ed affidabilità.

Estudio comparativo de la resistencia a la fractura de pilares de zirconia totalmente cerámicos y con base de titanio, en conexión externa e interna

Tesis inédita presentada en la Universidad Europea de Madrid. Facultad de Ciencias Biomédicas. Programa de Doctorado en Odontología Avanzada

Ceramic-veneered zirconia frameworks in full-arch implant rehabilitations: A 6-month to 5-year retrospective cohort study

Purpose: This was a retrospective cohort study designed to evaluate the clinical performance of ceramicveneered zirconia frameworks. Materials and Methods: Patients were recruited according to defined inclusion criteria. All patients were checked every 4 months from the time of definitive rehabilitation. At the end of 2013, all patients were rescheduled and rechecked for study purposes. The restorative procedures assessment was performed by previously established methods. The primary outcomes were the survival and success rates of the prosthesis. Descriptive statistics were used for the patient's demographics, implant distribution, and occurrence of complications. To study the survival and success of the prostheses, a Cox Regression analysis was used with a model constructed in a forward conditional stepwise mode. Predictive variables were included in the model, and adjusted survival curves were obtained for each outcome. Results: From 2008 to 2013, 75 patients were rehabilitated with 92 implant-supported, screw-retained, full-arch ceramic-veneered zirconia framework rehabilitations. The range of follow-up was between 6 months and 5 years. From the 92 full implant-supported screw-retained full-arch rehabilitations, Cox regression analysis indicated that within a 5-year time frame, the probability of framework fracture, major chipping, minor chipping, or any of the former combined to occur was 17.6%, 46.5%, 69.2%, and 90.5%, respectively. Conclusion: Results suggest zirconia as a suitable material for framework structure in implant-supported, full-arch rehabilitations. However, it experiences a high incidence of technical complications, mainly due to ceramic chipping. Further clinical studies should aim to ascertain the effects of clinical features and manufacturing procedures on the survival rates of these prostheses. © 2016 by Quintessence Publishing Co Inc.

Design and characterization of polymorphs and co-crystals of organic molecular semiconductors

In the last decades, organic semiconductors have attracted attention due to their possible employment in solution-processed optoelectronic and electronic devices. One of the advantages of solution processing is the possibility to process into flexible substrates at low cost. Organic molecular materials tend to form polymorphs, which can exhibit very different properties. In most cases, the control of the crystal structure is decisive to maximize the performance of the final device. Although organic electronics have progressed a lot, n-type organic semiconductors still lag behind p-type, presenting challenges such as air instability and poor solubility. NDI derivatives are promising candidates for applications in organic electronics due to their characteristics. Recently, the structure-properties relationship and the polymorphism of these molecules have gained attention. In the first part of this thesis, NDI-C6 thermal behavior was extensively explored which revealed two different behaviors depending on the annealing process. This study allowed to define the stability ranking of the NDI-C6 bulk forms and to determine the crystal structure of Form γ at 54°C. Additionally, the polymorphic and thermal behavior of thin films of NDI-C6 was also explored. It was possible to isolate pure Form α, Form β, Form γ and a new metastable Form ε. It was also possible to determine the stability ranking of the phases in thin films. OFETs were fabricated having different polymorphs as active layer, unfortunately the performance was not ideal. During the second part of this thesis, core-chlorinated NDIs with fluoroalkyl chains were studied. Initially, the focus was on the polymorphism of CF3-NDI that revealed a solvate form with a very interesting molecular arrangement suggesting the possibility to form charge transfer co-crystals. In the last part of the thesis, the synthesis and characterization of CT co-crystal with different NDI derivatives, and acceptor and as donor BTBT and ditBu-BTBT were explored.

Study and characterization of polymorphs of BTBT derivatives and their application in organic electronics

The perquisites of organic semiconductors (OSCs) in the field of organic electronics have attracted much attention due to the advantages like cost-effectiveness, solution processibility, etc. A key property in OSCs is charge carrier mobility, which depends on molecular packing, as even the slightest changes in the packing of OSC can significantly impact the mobility. Organic molecules are constructed by weak interactions, which makes the OSCs prone to adopt multiple packing arrangements, thus giving rise to polymorphism. Therefore, polymorph screening in bulk and thin films is crucial for material development. This thesis aims to present a systematic study of polymorphism of [1]benzothieno[3,2-b]benzothiophene (BTBT) derivatives functionalized with different side chains. The role of peripheral side chains has been studied since they can promote different packing arrangements. The bulk polymorph screening of OSCs was approached with conventional solution mediated recrystallization experiments like evaporation, slurry maturation, anti-solvent precipitation, etc. Each of the polymorphs were inspected for their relative stability and the kinetics of transformation was evaluated. Polymorphism in thin films was also investigated for selected OSCs. Non-equilibrium methods like, thermal gradient and solution shearing were employed to examine the nucleation, crystal growth and morphology in controlled crystallization conditions. After careful analysis of crystal phases in bulk and thin films, OFETs have been fabricated by optimizing the manufacturing conditions and the hole mobility values were extracted. The charge transport property of the OSCs tested for OFETs was supported by the ionization potential and transfer integrals calculation. An attempt to correlate the solid-state structure to electronic properties was carried out. For some of the molecules, mechanical properties have been also investigated, as the response to mechanical stress is highly susceptible to packing arrangements and the intermolecular interaction energy contributions. Additionally, collaborative research was carried out by solving and analysing the crystal structures of six oligorylene molecules.

Effect Of Platform Connection And Abutment Material On Stress Distribution In Single Anterior Implant-supported Restorations: A Nonlinear 3-dimensional Finite Element Analysis.

Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance. The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method. Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4×13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts. The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material. The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.

Biofilm And Saliva Affect The Biomechanical Behavior Of Dental Implants.

Friction coefficient (FC) was quantified between titanium-titanium (Ti-Ti) and titanium-zirconia (Ti-Zr), materials commonly used as abutment and implants, in the presence of a multispecies biofilm (Bf) or salivary pellicle (Pel). Furthermore, FC was used as a parameter to evaluate the biomechanical behavior of a single implant-supported restoration. Interface between Ti-Ti and Ti-Zr without Pel or Bf was used as control (Ctrl). FC was recorded using tribometer and analyzed by two-way Anova and Tukey test (p<0.05). Data were transposed to a finite element model of a dental implant-supported restoration. Models were obtained varying abutment material (Ti and Zr) and FCs recorded (Bf, Pel, and Ctrl). Maximum and shear stress were calculated for bone and equivalent von Misses for prosthetic components. Data were analyzed using two-way ANOVA (p<0.05) and percentage of contribution for each condition (material and FC) was calculated. FC significant differences were observed between Ti-Ti and Ti-Zr for Ctrl and Bf groups, with lower values for Ti-Zr (p<0.05). Within each material group, Ti-Ti differed between all treatments (p<0.05) and for Ti-Zr, only Pel showed higher values compared with Ctrl and Bf (p<0.05). FC contributed to 89.83% (p<0.05) of the stress in the screw, decreasing the stress when the FC was lower. FC resulted in an increase of 59.78% of maximum stress in cortical bone (p=0.05). It can be concluded that the shift of the FC due to the presence of Pel or Bf is able to jeopardize the biomechanical behavior of a single implant-supported restoration.

Effect of culture medium on biocalcification by Pseudomonas Putida, Lysinibacillus Sphaericus and Bacillus Subtilis

The objective of this study is to investigate the efficiency of calcium carbonate bioprecipitation by Lysinibacillus sphaericus, Bacillus subtilis and Pseudomonas putida, obtained from the Coleção de Culturas do Instituto Nacional de Controle de Qualidade em Saúde (INCQS), as a first step in determining their potential to protect building materials against water uptake. Two culture media were studied: modified B4 containing calcium acetate and 295 with calcium chloride. Calcium consumption in the two media after incubation with and without the bacterial inoculum was determined by atomic absorption analysis. Modified B4 gave the best results and in this medium Pseudomonas putida INQCS 113 produced the highest calcium carbonate precipitation, followed by Lysinibacillus sphaericus INQCS 414; the lowest precipitation was produced by Bacillus subtilis INQCS 328. In this culture medium XRD analysis showed that Pseudomonas putida and Bacillus subtilis precipitated calcite and vaterite polymorphs while Lysinibacillus sphaericus produced only vaterite. The shape and size of the crystals were affected by culture medium, bacterial strain and culture conditions, static or shaken. In conclusion, of the three strains Pseudomonas putida INQCS 113 in modified B4 medium gave the best results precipitating 96% of the calcium, this strain thus has good potential for use on building materials.

Crystallite size-dependent phases in nanocrystalline ZrO(2)-Sc(2)O(3)

ZrO(2)-10, 12 and 14 mol% Sc(2)O(3) nanopowders were prepared by using a nitrate-lysine gel-combustion synthesis. These materials were studied by synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy after calcination at different temperatures from 650 to 1200 degrees C, which led to samples with different average crystallite sizes, up to about 100 nm. The results from SXPD and Raman analyses indicate that, depending on Sc(2)O(3) content, the metastable t ''-form of the tetragonal phase or the cubic phase are fully retained at room temperature in nanocrystalline powders, provided an average crystallite sizes lower than similar to 30 nm. By contrast, powders with larger average crystallite sizes exhibit the stable rhombohedral, beta and gamma, phases and do not retain or very partially retain the metastable t '' and cubic ones.