Ipek Akin

Oxygen-loss in A-site deficient Sr0.85La0.10TiO3 perovskite

The electrical properties of Sr1−3xLa2xTiO3 ceramics (x = 0.05, LST) change dramatically with sintering temperature and atmosphere. Ceramics sintered at 1200 °C in both O2 and N2 exhibit near intrinsic band-type conduction with bulk conductivity ∼10−7 S cm−1 at 500 °C and activation energy for conduction, Ea of ∼1.6–1.8 eV. LST ceramics sintered at 1450 °C in O2 exhibit much higher bulk conductivity (>10−4 S cm−1 at −50 °C) with an Ea ∼ 0.16 eV. For LST ceramics sintered at 1450 °C in N2, the bulk conductivity was too high to be measured by impedance spectroscopy even at 10 K. In addition, electrical heterogeneity is observed in LST pellets sintered at 1450 °C under both O2 and N2 where pellet outer surfaces are more resistive than the inner regions of the ceramic. The defect chemistry of Sr0.85La0.10TiO3 perovskite is discussed based on chemical doping and oxygen-loss mechanisms and we highlight the importance of A-site vacancies on the oxygen-loss mechanism in La-doped ST-based ceramics.

Spark plasma sintered Al2O3–YSZ–TiO2 composites: Processing, characterization and in vivo evaluation

Al2O3 and Al2O3-YSZ composites containing 3 and 5 wt.% TiO2 were prepared by spark plasma sintering at temperatures of 1350-1400°C for 300s under a pressure of 40 MPa. The grain growth of alumina was suppressed by the addition of YSZ. Al2O3-YSZ composites showed higher hardness than monolithic Al2O3. There was not a considerable difference in hardness values for Al2O3-YSZ composites containing 10 and 20 vol.% YSZ and the addition of TiO2 decreased the hardness of the composites. The fracture toughness of Al2O3 increased from 2.8 MPa·m(1/2) to 4.3 MPa·m(1/2) with the addition of 10vol.% YSZ, further addition resulted in higher fracture toughness values. The fracture toughness values were increased with TiO2 addition and the highest value of fracture toughness, 5.3 MPa·m(1/2), was achieved with the addition of 20 vol.% YSZ and 5 wt.% TiO2. Preliminary in vivo tests demonstrated the biocompatibility and osseointegration of the composites after 6 week post-implantation in femur of Wistar rats.

Effect of CeO2 Addition on In Vitro Bioactivity Properties of K-Mica-Fluorapatite Based Glass Ceramics

The aim of this study is to investigate the crystallization behavior and in-vitro bioactivity character of glass ceramics having 3:7 weight ratio of fluorapatite (Ca10(PO4)6F2) to potassium mica (K2Mg3AlSi3O10F2) as a function of cerium oxide addition, and compare the morphology of hydroxycarbonate apatite (HCA) layer formation depending on cerium oxide addition.

Titania versus Ceria Alumina/Zirconia Composites: Structural Aspects and Biological Tolerance

The aim of our study is to compare the structural and biological tolerance of novel Al2O3/3Y-TZP composites with ceria respectively titania addition (5 wt%). Scanning electron microscopy, X-ray diffraction, infrared spectroscopy and XPS results are reported for structural characteristics and surface modifications upon different fluoride treatments. The biocompatibility of the samples was evaluated using an animal model (rabbit). The explants were analyzed at a specific period (6 weeks).The sections of implanted bone area were subjected to histological evaluation. Upon correlating the structural properties and in vivo evaluation, we concluded that the addition of both TiO2 and CeO2 to Al2O3/3Y-TZP implies similar properties and satisfactory biological tolerance. With respect to the surface treatment, qualitative and quantitative results show that the alumina/zirconia with titania addition are more sensitive to fluoride treatment.

Correlation between Structural Properties and In Vivo Biocompatibility of Alumina/Zirconia Bioceramics

The aim of our study is the characterization and comparison of structural properties of two novel alumina/zirconia ceramics prepared by Spark Plasma Sintering and biocompatibility evaluation by using an animal model (Wistar rats). SEM, XRD and FTIR spectroscopic results are reported for structural characteristics. In vivo tests demonstrated the biocompatibility and osseointegration of the composites by complementary SEM and histological analysis of the defects in rat femur respectively the connective tissue.

Improving the Bioactivity and Biocompatibility of Acrylic Cements by Collagen Coating

Polymer-ceramic composites based on polymethyl methacrylate are widely used in orthopaedics as suture materials and fixation devices due to their biocompatibility and ability to support bony growth (osteoconductive) and also bone bioactive (to form a calcium phosphate layer on its surface). The aim of this study is to compare the microstructure, bioactivity and biocompatibility of new acrylic cement containing silver and collagen coated, with a comercial one, by in vitro study in simulated body fluid. In order to evaluate the properties of the surface layer, SEM microscopy and ATR-FTIR spectroscopy are used. The results indicates that both silver content and the presence of collagen layer favourise the mineralisation process at the surface.

Investigation of the microstructure and oxidation properties of NbB2-SiC-GNP composites

M solvothermal process was used to synthesize anatase TiO2 nanocrystallines for the application of dyesensitized solar cells (DSSCs). The morphologies and sizes of TiO2 could be simply controlled by using different kinds of alcohols where no additives were needed. By using isopropanol (IPA) as solvent, TiO2 in size of 20-30 nm with dominant {001}/{010} facets was obtained; whereas ultrafine anatase TiO2 of about 5 nm with dominant {101}-facet was obtained using octanol (OCT). To investigate the influences of TiO2 on the photovoltaic performances of DSSCs, three different pastes were fabricated using IPA, OCT and mixed IPA/OCT as photoanodes. The results revealed that the requirements of TiO2 photoanodes used at one sun and room light conditions were quite different. OCT showed the highest power conversion efficiency (PCE) up to 9.58% under one sun irradiation because of its high specific surface area that provided high dye-loading capacity. However, the great amount of grain boundaries appeared in OCT became disadvantageous at room light condition. On the other hand, IPA/OCT combined the features of IPA and OCT that was optimal for room light harvesting and its PCE reached 12.46% under 200 lux T5 lamp irradiation. The photovoltaic properties of three different photoanodes in correlation with their band structures, electronic transport behaviors and light harvesting efficiency in different lighting conditions will be carefully discussed in this presentation.G the increasing interest for the biomaterials in medical and engineering field, the objective of this talk is the theoretical and experimental analysis of the biomaterials in order to define experimental procedures and mathematical models suitable for their mechanical characterization. The biomaterials exhibit a rheological behavior intermediate between that of purely elastic materials and that of the purely viscous materials and therefore are called viscoelastic ones. In the past the “classical” models as Maxwell and Kelvin-Voigt have been used to capture viscoelastic phenomena. However, these models are not consistent to model the viscoelastic behavior of real materials, since the Maxwell type can capture the relaxation tests only and the Kelvin-Voigt the creep tests. A more realistic description of creep and/or relaxation is given by a power law function with real order exponent. As soon as we assume a power law function for creep, the constitutive law relating deformation and stress is ruled by a Riemann-Liouville fractional integral with order equal to that of the power law. In this regard, recent studies have been stressed that the most suitable model for capturing the viscoelastic behavior is the spring-pot, characterized by a fractional constitutive law. Based on the aforementioned considerations, it is apparent that the need of theoretical as well as experimental development and exploration of materials with novel physical characteristics. For instance, if the giant grass Arundo donax (AD) has to be characterized; then, attention is devoted on searching a proper model for characterizing the behavior of giant reeds. To aim at this, firstly, meticulous experimental tests have been performed in the Laboratory of structural materials of University of Palermo. Further a novel aspect of using an advanced Euler-Bernoulli model to fit experimental data of bending tests will be introduced.M devices represent an emerging technology with a great potential in analytical life sciences. In particular lab-on-a-chip concerning genomic applications has attracted great interest; in such systems there is often the need to provide an efficient DNA amplification by PCR (polymerase chain reaction). Nowadays, polymers are the materials of choice for the fabrication of micro devices for genomic applications. For prototyping and small-scale production, soft lithographyA family of multiple-step techniques based on molding the thermally curable elastomer polydimethylsiloxane (PDMS) is the current gold standard. However, the commercial and common thermally curable PDMS shows some drawbacks that limit its applicability in biotechnology, such as the difficulty in controlling and modifying the surface chemistry and in tuning the physical and mechanical properties of the material. An appealing alternative to thermally curable PDMS prototyping is the use of specially designed UV curable polymers, as photopolymerization is a very fast reaction that leads to the synthesis of highly cross-linked networks in few seconds at room temperature. Moreover, this technique can be applied to a wide variety of photocurable polymers, allowing to select and tune the desired physico-chemical properties of the final device. In the present work, we introduce the use of a class of photocurable siloxane polymers for the fabrication of microfluidic devices for biomedical applications (i.e., PCR). New multifunctional acrylic oligomers are synthesized (Figure 1a) and then photo cross linked. Moreover, copolymerization is used as strategy to optimize the photopolymer properties. The polymers and copolymers synthesized are suitable for bio microfluidics: they are PCR compatible (Figure 1b), highly resistant to temperature and various solvents, transparent, dimensionally stable and essentially non-permeable to water vapor. Therefore, these materials are used to fabricate microfluidic devices (Figure 1c), in which PCR is successfully conducted as proof of principle.

Production and Characterization of Hydroxyapatite-Zirconia Composites

Abstract Hydroxyapatite (HA) ceramics are used extensively in different medical applications, such as biomaterial for repair or replacement of bone tissues since it resembles mineral component of bone and teeth. However, HA exhibits low fracture toughness due to its lack of strength and brittleness, thereby providing an obstacle to its application in implants that must withstand to high loads. In this study, HA was synthesized from human teeth by using a single calcinations method. Hydroxyapatite powders were mixed with different amounts of zirconia. The composites were sintered at different temperatures and characterized in terms of mechanical properties and the optimum sintering temperature was determined for good mechanical properties.

In-Vitro Bioactivity Characterization of Sodium-Potassium Mica and Fluorapatite Containing Glass Ceramics

The aim of this study is to find out the crystallization behaviour and in-vitro bioactivity character of machinable glass ceramics having different ratios of Na/K mica and apatite phases, to ascertain the best machinable composition. In order to investigate the bioactivity behavior of the samples the simulated body fluid (SBF) was prepared. Samples were removed from the solution after 1 hour, 1 day, 1, 2, 3 and 4 weeks. FEG-SEM was used to characterize the morphology of precipitation HCA layer on the surface depending on time. Molecular bonding characterization of HCA layers were carried out by using Fourier Transform Infrared Spectroscopy (FTIR) technique. The thin film X-ray diffraction (TF-XRD) analysis was used to characterize the variation of chemical composition on precipitated layer by time. Optimum results were obtained by the composition, containing 70wt% Na/K mica and 30wt% fluorapatite which had an average mica size of 3-4 microns.

In Vitro Bioactivity Characterization of K-Mica-Fluorapatite Based Glass Ceramics Containing Varying Amount of TiO2 Addition

The purpose of this study is to investigate the crystallization behavior and in-vitro bioactivity character of glass ceramics having 3:7 weight ratio of flourapatite (Ca5(PO4)3F) to potassium mica (K2Mg3AlSi3O10F2) as a function of titania addition, and compare the morphology of hydroxycarbonateapatite (HCA) layer formation depending on titania addition on ceramic composition. It is observed from microstructural investigations that there is no morphology change occurred on precipitated HCA layer depending on nucleating agent in glass-ceramics. TF-XRD analysis indicates that after precipitation of initial particulates, crystallization proceeds and crystallization of precipitated HCA phase increases by increasing the time. It is observed that Ca, P ion variation in solution has two stage in terms of precipitation’ first stage represents formation of amorphous HCA and the second stage is related with crystallization. FTIR analysis strongly supports TF-XRD analysis as well.