Juliana Marchi

Analysis in vitro of the cytotoxicity of potential implant materials. I: Zirconia-titania sintered ceramics

Zirconia (ZrO2) is a bioinert, strong, and tough ceramic, while titania (TiO2) is bioactive but has poor mechanical properties. It is expected that ZrO2-TiO2 mixed ceramics incorporate the individual properties of both ceramics, so that this material would exhibit better biological properties. Thus, the objective of this study was to compare the biocompatibility properties of ZrO2-TiO2 mixed ceramics. Sintered ceramics pellets, obtained from powders of TiO2, ZrO2, and three different ZrO2-TiO2 mixed oxides were used. Roughnesses, X-ray diffraction, microstructure through SEM, hardness, and DRIFT characterizations were performed. For biocompatibility analysis cultured FMM1 fibroblasts were plated on the top of disks and counted in SEM micrographs 1 and 2 days later. Data were compared by ANOVA complemented by Tukeys test. All samples presented high densities and similar microstructure. The H2O content in the mixed ceramics was more evident than in pure ceramics. The number of fibroblasts attached to the disks increased significantly independently of the experimental group. The cell growth on the top of the ZrO2-TiO2 samples was similar and significantly higher than those of TiO2 and ZrO2 samples. Our in vitro experiments showed that the ZrO2-TiO2 sintered ceramics are biocompatible allowing faster cell growth than pure oxides ceramics. The improvement of hardness is proportional to the ZrO2 content. Thus, the ZrO2-TiO2 sintered ceramics could be considered as potential implant material.

Physico-chemical characterization of zirconia-titania composites coated with an apatite layer for dental implants.

OBJECTIVES To investigate the crystalline phases, morphological features and functional groups on the surface of sintered Y:TZP/TiO2 composite ceramics before and after the application of a biomimetic bone-like apatite layer. The effect of TiO2 content on the composites characteristics was also evaluated. METHODS Samples of Y:TZP containing 0-30mol% TiO2 were synthesized by co-precipitation, followed by filtration, drying and calcination. The powders were uniaxially pressed and sintered at 1500°C/1h. To obtain biomimetic coatings the samples were exposed to sodium silicate solution and then to a concentrated simulated body fluid solution. The surfaces, before and after coating, were characterized by diffuse reflectance infrared Fourier transformed spectroscopy, X-ray diffraction analysis and scanning electron microscopy. RESULTS The surfaces of all Y:TZP/TiO2 samples were covered with a dense and uniform calcium phosphate layer with a globular microstructure. This layer was crystalline for specimens with 30% of TiO2 and amorphous for specimens with 0 and 10% of TiO2. Chemical analysis indicated that this layer was composed of type A carbonate apatite. Among the materials tested, the composite with 10% of TiO2 showed the best overall chemical and physical features, such as higher density and more cohesive amorphous apatite layer. SIGNIFICANCE Y-TZP-based materials obtained in the present investigation by means of the successful association of a calcium phosphate biomimetic layer with small amounts TiO2 should be further explored as an option for ceramic dental implants with improved bioactivity.

Hydroxyapatite coating on silicon nitride surfaces using the biomimetic method

Silicon nitride based ceramics are promising candidates for biomedical applications due to their chemical and dimensional stability associated to suitable mechanical strength and relatively high fracture toughness. However, the bioinert characteristics of these ceramics limit their application to situations where the formation of chemical bonds between the material and the tissue are not essential. A way to broaden the application field of these ceramics in medicine is promoting their bioactivity by means of a hydroxyapatite coating. Therefore, in this paper, samples of silicon nitride were coated with apatite using the biomimetic method. The treated silicon nitride surface was characterized by diffuse reflectance infrared Fourier transformed, X ray diffraction and scanning electron microscopy. The results showed that a layer of hydroxyapatite could be deposited by this method on silicon nitride samples surface.

Cell response of calcium phosphate based ceramics, a bone substitute material

The aim of this study was to characterize calcium phosphate ceramics with different Ca/P ratios and evaluate cell response of these materials for use as a bone substitute. Bioceramics consisting of mixtures of hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) powders in different proportions were pressed and sintered. The physical and chemical properties of these bioceramics were then characterized. Characterization of the biological properties of these materials was based on analysis of cell response using cultured fibroblasts. The number of cells attached to the samples was counted from SEM images of samples exposed to cell culture solution for different periods. These data were compared by analysis of variance (ANOVA) complemented by the Tukeys test. The TCP sample had higher surface roughness and lower density. The adherence and growth of FMM1 cells on samples from all groups was studied. Even though the different calcium based ceramics exhibited properties which made them suitable as bone substitutes, those with higher levels of β-TCP revealed improved cell growth on their surfaces. These observations indicated two-phase calcium phosphate based materials with a β-TCP surface layer to be a promising bone substitute.

Influence of additive system (Al2O3-RE2O3 , RE = Y, La, Nd, Dy, Yb) on microstructure and mechanical properties of silicon nitride-based ceramics

Silicon nitride based ceramics have been widely used as structural ceramics, due mainly to their thermo-mechanical properties such as high density, high thermal shock resistance, corrosion resistance and chemical stability. The aim of this study was to determine the influence of rare earth and aluminum oxide additions as sintering aids on densification, microstructure and mechanical properties of silicon nitride. Silicon nitride mixtures with 91 wt. (%) Si3N4 and 9% wt. (%) additives were prepared and sintered. The density, microstructure and mechanical properties of the sintered specimens of these mixtures were determined. In most specimens, scanning electron microscopic examination and X ray diffraction analysis revealed elongated grains of β-Si3N4 with aspect ratio of about 2.0 and dispersed in a glassy phase. The density of the sintered specimens was higher than 94% of the theoretical density (td) and specimens with La2O3 and Al2O3 additions exhibited the highest value. The results of this investigation indicate that the rare earth ion size influences densification of silicon nitride, but this correlation was not observed in specimens containing two different rare earth oxides. The hardness values varied in direct proportion to the density of the specimens and the fracture toughness values were influenced by the composition of the intergranular glassy phase.

Dilatometric studies of (SiO2-RE2O3-Al2O3) silicon carbide ceramics

Silicon carbide is an important structural ceramic and finds applications as abrasives, as a refractory and in automotive engine components. This material can attain high densities during liquid phase sintering if suitable additives are used. Silicon carbides containing silica, alumina and rare earth oxides have suitable characteristics to promote liquid phase sintering. In this paper, the sintering behavior of silicon carbide ceramics with additives based on the (SiO2-RE2O3-Al2O3) system (RE = Y, Dy) has been studied. Samples with different compositions and containing 90 vol.% SiC were sintered in a dilatometer at 1950 °C/1h and in a graphite resistance furnace from 1500 °C/1h up to 1950 °C/1h. The shrinkage behavior as a function of rare earth oxide used and additive composition was also studied. The sintered materials were characterized by density and weight loss measurements. The crystalline phases were identified by X-ray diffraction analysis. The sintering kinetics of these materials can be related to the formation of secondary crystalline phases.

Bioactive glass plus laser phototherapy as promise candidates for dentine hypersensitivity treatment

Treatments for dentine hypersensitivity (DH) may produce positive effects, though do not have lasting results. We investigated the reparative potential of stem cells derived from deciduous teeth (SHEDs) in response to components delivered from substances used in the treatment of the DH, associated or not to laser phototherapy (LPT), to stimulate dentine formation. SHEDs were submitted to substances delivered from a laboratorial P-rich bioactive glass [57SiO2 -26CaO-17P2 O5 (wt %)] or a commercially available desensitizer (Gluma® Desensitizer), associated (or not) to LPT (InGAlP diode laser, 660 nm, 0.028 cm2 , 20 mW, 5 J/cm2 , 7 s, contact mode). Biomaterial characterization was performed by X-ray diffraction, scanning electron microscopy and the particle size was evaluated by dynamic light scattering. SHEDs proliferation and differentiation were analyzed by MTT and Alizarin Red staining, respectively. The conditioned media used in these tests were evaluated regarding their pH and the ionic concentration changes due to ions leached from the bioactive glass (BG). BG majority presented a non-crystalline solid structure and mixed particle sizes characterized by the agglomeration of nanoparticles. Cultures treated with BG alone or in association to LPT showed improved cell growth in relation to Gluma® (p < 0.05). Gluma® was cytotoxic in all tested conditions, regardless irradiated or not. BG associated to LPT induced intense mineral matrix formation. In conclusion, BG releases ionic dissolution products able to promote SHEDs differentiation. BG associated to LPT improves SHEDs proliferation and differentiation in vitro, and may be a promise therapeutic approach for the DH treatment.

Mechanical Characterization of Tricalcium Phosphate Ceramics Doped with Magnesium

In this work, the mechanical properties of magnesium doped tricalcium phosphate ceramics, considered a bioceramic for bone repair applications, were studied. Pure β-TCP and β-TCP doped with 2.25 mol% of Mg powders were synthesized through neutralization, freeze dried, uniaxially pressed and sintered at 1200°C/1h. The mechanical properties were evaluated through four points flexural and compression strength tests, fracture toughness and Youngs Modulus. After the flexural strength test, the fractures surface and their homogeneity were characterized by scanning electron microscopy. It was verified that Mg addition into β-TCP structure lead higher linear shrinkage, followed by higher residual stress, decreasing the mechanical properties compared to pure β-TCP ceramics. However, this behavior does not hinder the use of such bioceramics as bone substitutive materials, mainly in the sites that do not require high mechanical solicitations.

Biocompatible Glasses for Cancer Treatment

Treatment of cancer is an old issue in the history of medicine. Millions cases are reported every year, as well as millions of cancer-related deaths are also registered. The development of new technologies is changing this scenario, and new cancer treatment techniques have been included in the clinical routine. Among these techniques, hyperthermia and brachytherapy have an interesting prominence. Hyperthermia has been suggested as an auxiliary therapy for cancer treatment, while brachytherapy offers the opportunity of delivering high dose beta radiation emission into the cancerous tissue. In this chapter, we pointed out the use of biocompatible glasses (please consult the Editor’s note in order to clarify the usage of the terms bioglass, bioactive glass and biocompatible glasses) for cancer treatment by either hyperthermia or brachytherapy. A quick review about hyperthermia is provided, and the main compositions of biocompatible glasses used in hyperthermia are discussed regarding their magnetic and biological properties. In addition, few glasses with suitable radiological properties with potential application in prostate cancer and liver cancer are reviewed, as well as new possible glasses composition are considered from the point of view of Monte Carlo and molecular dynamics simulations.

Sol-Gel Synthesis of Amorphous Silica Nanoparticles: Study of the Process Parameters Influence on Structure and Particle Size Distribution

The synthesis of silica particles at the nanoscale through the sol-gel method is of great interest due to their potential use in industrial applications. The Stöber method is the most used method for the silica nanoparticles production using ammonia as a catalyst. This work studied the sol-gel synthesis of amorphous silica nanoparticles described by Stöber, in order to evaluate the influence of the variation of the process parameters (molar ratio water/TEOS = 25 and 55, reagent feed rate = 0.6 mL/min and 18 mL/min, pH = 12 and 9 and reaction time of 0, 5, 30, 60 and 120 minutes) on the particle size distribution and structural functional groups. The particle size distribution was analyzed by dynamic light scattering (DLS) and the structural functional groups was analyzed by infrared spectroscopy through Fourier transform (FTIR). The molar ratio water/TEOS influenced the functional groups presents and the time influenced the particle diameter distribution. It was not possible to identify the influence of the feed rate and pH in the results. The particle diameters found were between 200-500nm. This result may be occurred due to mass diffusion and/or nanoparticles aggregation.