Key Engineering Materials Vol. 587

Abstract: The aim of the present study is to measure the optical properties of dental materials, color and translucency, as well as their radiopacity using digital images. To do this, an original software application implementing two functions has been developed. Determining the radiopacity amount of certain areas of the materials is achieved by interpolating the values of ten aluminum plates used as reference. The study of this property is achieved by interpreting the statistical results and graphs displayed. The translucency value was calculated as the difference of the CIELab color system values for two digital images representing the same material on white and black background, respectively. In order to evaluate the color changes of the biomaterials, the samples were immersed in coffee, wine and orange juice. The application has been tested on several experimental materials based on bioceramics, dental composites and giomers, and the results are similar to the ones obtained using other evaluation methods.

Abstract: The present study concerns the production and characterization of porous hydroxyapatite/niobo-phosphate glass ceramics to be used for bone repair. The scaffolds were produced by hydrothermal deposition of monetite on polyurethane sponge substrates, further converted to hydroxyapatite in an alkali solution. After heat treatment, elimination of the organic sponge provides a three-dimensional (3D) structure. Niobo-phosphate glasses were added to the heat treated struts and the scaffolds were sintered. The porous bodies were characterized by field-emission gun scanning electron microscope (FEG-SEM) with energy-dispersive X-ray spectroscopy (EDS).

Abstract: The influence of the grain size of alumina and zirconia ceramics on the spreading and adhesion of MG63 cell lines was investigated. Single-component ceramics and layered composite ceramics were prepared by electrophoretic deposition, uniaxial pressing and sintering. The grain size of zirconia was 100 nm to 2.7 μm and that of alumina was 0.5 μm to 1.5 μm. Subsequently, sample surfaces were polished and thermally etched. Biological tests of adhesion (0.5 to 8 h) were used to evaluate the influence of grain size on biological response. The highest cell spreading was obtained for ZrO₂ ceramics with an average grain size of 100 and 120 nm. The cell selection was observed on layered ZrO₂/Al₂O₃ composites. The cells predominantly adhered to ZrO₂ layers. The results showed a positive influence of nanostructured ceramic surfaces on biological behaviour of MG63 cells.

Abstract: Various kinds of materials have been found to bond to living bone and some of them are clinically used as important bone substitutes. However, they can not be used under load-bearing conditions, since their fracture toughness are not so high as that of human cortical bone. All of them are based on calcium phosphate or silicate. The present authors recently showed that even Ti metal and its alloys having high fracture toughness can show bone-bonding bioactivity, if they are subjected to simple chemical and heat treatments to form some kind of titanium oxide or titanates on their surfaces. They can show not only bone-bonding property, but also novel functions such as osteoinduction, release of antibacterial or bone-growth promoting ions etc.

Abstract: Hydroxyapatite (HA), one of the calcium phosphate compounds, is the most widely used bioceramic. HA materials have a common usage in bone repairing due to its ability to accelerate the bone growth around the implant. HA is a biocompatible material and used in production of various kinds of prosthesis, repairing the cracked or broken bones and coating of metallic biomaterials. This study covers production and characterization of composite materials made of commercial synthetic hydroxyapatite (CSHA) with commercial inert glass, magnesium oxide and niobium (V) oxide additions (5 and 10 wt%), seperately. These additives used as reinforcement materials to improve the mechanical properties of CSHA based composites. The composites were subjected to sintering at different temperatures between 1000oC and 1300oC, then microstructures and mechanical properties of CSHA composites were investigated. The physical and mechanical properties were determined by measuring density, compression strength and Vickers microhardness (HV). Structural characterization was carried out with X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies. In all composites, density values and mechanical properties increased with increasing sintering temperature. CSHA composite with 5 wt% CIG addition showed highest physical and mechanical properties among all CSHA composites produced in this study.

Abstract: Functional ceramic nanopowders with emphasis on biomedical applications were engineered by gas-phase condensation using the CO₂ laser vaporization (LAVA) technique. Europium doped strontium aluminate nanoparticles (NP) were prepared from a SrO/α-Al₂O₃/Eu₂O₃ powder mixture. Excited with ultraviolet radiation (UV), the as-prepared amorphous NP revealed red photoluminescence emission. After annealing in reductive atmosphere crystalline SrAl₂O₄:Eu²⁺ nanopowder was obtained showing strong green emission at UV excitation. Ferrimagnetic iron oxide (Fe_xO_y) nanopowders were prepared starting from α-Fe₂O₃ powder. In oxygen-free condensation atmosphere γ-Fe₂O₃ NP were obtained. Oxygen as condensation gas yielded γ-and ε-Fe₂O₃ NP. Superparamagnetic NP were prepared starting from α-Fe₂O₃/SiO₂ mixtures. Depending on the mixing ratio γ-Fe₂O₃ nanocrystallites embedded in a SiO₂ glass matrix or γ-Fe₂O₃-SiO₂ Janus NP were obtained. These NP provide a reactive SiO₂ interface for subsequent functionalizing. The co-vaporization of α-Al₂O₃ as the main proportion and t-ZrO₂ yielded zirconia-toughened-alumina NP. Reinforcing effects of Al₂O₃-ZrO₂ dispersion ceramics will be increased using NP with an intraparticle dispersion of these phases. Future applications of the LAVA prepared NP include biological fluorescence labeling, and drug targeting, magnetic resonance imaging, and hyperthermic cancer therapy, as well as sintering of load bearing ceramic implants, respectively.

Abstract: When pH or temperature of simulated body fluid (SBF) is raised, fine particles of calcium phosphate are precipitated. We found that this fine particle actively induces hydroxyapatite from body fluid or SBF and named the particle Apatite Nucleus (AN). In this study, we attached AN on the surface of γ-Fe₂O₃ nanoparticles and soaked them in SBF. By this treatment, hydroxyapatite was induced from AN and covered the whole surface of the γ-Fe₂O₃ nanoparticles, then hydroxyapatite microcapsule encapsulated γ-Fe₂O₃ was fabricated. We dispersed the microcapsules in urease solution, and collected the microcapsules by neodymium magnet. It was indicated that the urease was adsorbed to the hydroxyapatite microcapsules and collected by the magnetism of γ-Fe₂O₃ successfully.

Abstract: Micropores were formed on the surface of polylactic acid (PLA) plate by doubled sandblasting process using alumina particles with 14.0 μm for average particle size as first process, then using the particles with 3.0 μm for average particle size as second process. Apatite Nucleus (AN) was precipitated in the pores. By these treatments, bioactive AN precipitated PLA was fabricated. Bioactivity of the AN precipitated PLA was examined by soaking in SBF and it was observed that hydroxyapatite was induced on the surface of the PLA within 1 d. High adhesive strength of hydroxyapatite layer was achieved due to a mechanical interlocking effect between hydroxyapatite formed in the micropores and the PLA plate.

Abstract: nclusion of zinc in apatites is not completely understood due to complexes in solution preventing the incorporation or the inclusion of defects. Some work has shown zinc addition by alternative synthesis routes, but the level of incorporation has not been reassessed. This work uses a newly developed approach whereby zinc is included in an amorphous phase and subsequently crystallized. Different phosphate reactants (ammonium, sodium or potassium phosphates) were mixed together with calcium salts (calcium nitrate or calcium acetate) and the pH level adjusted (with ammonia or KOH) to investigate the ease of forming an amorphous phase and the inclusion of zinc. X-ray diffraction revealed that all reactants showed a tendency to form an amorphous phase, supporting the requirement of a high pH to prevent crystallization. X-ray fluorescence showed higher inclusion in the absence of ammonia. Potassium phosphate led to the highest zinc incorporation, accompanied by simultaneous inclusion of potassium. Crystallization at 700 °C indicated that zinc levels close to 20% replacement of calcium were the highest possible before the onset of tricalcium phosphate formation. FTIR-DRIFT showed a change in bonding conditions at higher zinc concentrations. This work shows the importance of reactants for including zinc, the larger zinc inclusion accompanied by potassium and zinc levels that can maintain the apatite structure.

Abstract: Composite materials based on collagen matrix could have the different properties in the case of reinforcement with different bioceramics. Not just the chemical composition of bioceramics used as reinforcement component have an influence on the composite properties, but also the microstructural aspects of bioceramics such as morphology, grain size and shape, homogeneity and distribution. We present in this paper the effect of the bioceramics type (TCP, hydroxyapatite) and ratio on the composite material structure and the biodegradation properties of some collagen based composites obtaining using the freeze-drying process. Also, we measure the porosity before made the biodegradation test using collagenase as medium and immersion in simulated body fluid in order to see the bioactivity properties.