Key Engineering Materials Vols. 396-398

Abstract: An hydrated putty was prepared by mixing submicron particles, rounded particles and granules of Biphasic Calcium Phosphate (BCP) ceramics composed of HA and β-TCP phases. The material filled entirely critical sized defects in the femoral epiphysis of NZW rabbits. After 3, 6 and 12 weeks, histology revealed that submicron particles were rapidly degraded by multinucleated TRAP-positive cells. This osteoclastic resorption stimulated bone ingrowth while the large BCP particles served as scaffold supporting bone healing by osteoconduction.

Abstract: In the present work, mechanical properties of a stoichiometric hydroxyapatite (HA), synthesized by hydrothermal method, with 1.66 Ca/P molar ratio are investigated as a function of the processing parameters. Cylindrical samples were processed by uniaxial compacting, followed by sintering, aiming to obtain high density HA samples. Density values were obtained by the geometric method and SEM images were taken from HA samples in order to characterize their topography and to determine the grain size for each set of samples. Vickers micro-hardness was measured for each set of samples. Compressive strength of cylindrical samples with 2.0 mean diameter/height ratio was measured reporting load to failure divided by the cross-sectional area of the samples. Vickers micro-hardness and compaction strength values of the samples were found to be in agreement with the relative density and grain size values.

Abstract: The aim of this work is the synthesis of α-tricalcium phosphate by solution combustion synthesis using urea as combustible in the stoichiometric ratio and with excess of combustible. The salts Ca(O3)2.4H2O and (H4)2HPO4 were used as reaction precursors with Ca/P ratio of 1.5. The pH adjustment was made adding nitric acid. A porous foam composed by β-tricalcium phosphate, hydroxyapatite and α or β-dicalcium pyrophosphate were obtained as reaction product. X-ray diffraction was used to identify the phases. The obtainment of α-TCP was possible after a heat treatment where the material was held at 1250°C for 15 hours followed by quenching. Smaller particle size was obtained when four times the stoichiometric ratio of combustible was used in the reaction. α-TCP samples were immersed in SBF in order to verify the biocompatibility.

Abstract: X-ray amorphous tricalcium-phosphate nanoparticles (ATCP) produced by flame spray synthesis were heat-treated at temperatures between 500 and 1000 °C and analyzed in situ by X-ray powder diffraction. The main phase occurring after crystallisation at 525 °C was α-TCP, minor phases were identified as β-TCP and hydroxyapatite. More elevated temperatures induced crystallite growth and the transformation of α-TCP into β-TCP. Above 900 °C no α-TCP was traceable anymore. α’-TCP was not observed in the experiment. This study shows that nanoparticulate α-TCP can be obtained by thermal treatment of an amorphous TCP nanoparticle in a temperature range where sintering effects such as particle growth and densification are moderate or nearly negligible.

Abstract: he preparation of different pore diameter and thickness nanoporous alumina membranes by two-step anodic oxidation, and the corrosion resistance and mechanical properties of the alumina membrane were investigated. In order to show the infection of pore diameter and thickness on these properties, the dynamic polarization and nano indentation method were mentioned, at the same time hemolytic test was performed for testing biocompatibility of the membrane.

Abstract: Several CAD/CAM systems are available to dental prosthesis laboratories which can be used to fabricate all-ceramic copings and frameworks. The use of these systems presents low demand, due principally the high blocks ceramics cost used for theses systems. Usually, these ceramic blocks are sintered at high temperatures, between 1450 and 15500C, resulting in micrometric ZrO2 microstructure. A considerable innovation in these ceramics systems used in CAD/CAM applications was introduced by the use of nanometric-tetragonal ZrO2 blocks, which are sintered at low sintering temperatures resulting in nanometric grains morphology and improved mechanical properties. The purpose of the present work is to characterize the mechanical properties of nanoparticled zirconium oxide blocks comparing with commercial micrometric ceramic parts. XRD patterns showed that the blocks have only the tetragonal-ZrO2 as crystalline phase. The tetragonal-monoclinic transformation phase was responsible for the excellent mechanical properties. Nanometric blocks presented hardness of 13GPa, fracture toughness of 11MPam1/2 , bending strength of 1020MPa and Weibull modulus, m=14, while micrometric ZrO2 blocks similar hardness, fracture toughness 8.5MPam1/2, bending strength of 850MPa and Weibull modulus of 10.

Abstract: The aim of this study was to investigate the sol gel synthesis of HA/FA nanoparticles and the possible formation of TCP phase or unstoichiometric calcium deficient hydroxyapatite (CDHA) from the precursors with a Ca/P ratio of 1.62. In order to prepare the sol, the solutions of Triethyl phosphite, ammonium fluoride and calcium nitrate in ethanol were used respectively as P, F and Ca precursors. The crystallinity, particle and crystallite size, powder morphology, chemical structure and phase analysis were investigated by SEM, XRD, FT-IR and Zeta sizer experiment. A multiphase compound containing hydroxyapatite (HA) and fluoroapatite (FA) nanoparticles and calcium deficient hudroxyapatite (CDHA) agglomerates was obtained. The size of the crystallites estimated from XRD patterns using Scherrer equation and the crystallinity of HA phase were about 5 nm and 66% respectively. The zeta sizer experiments for the dispersed particles in its own conditions showed an average size of 98 nm.

Abstract: B-type carbonate apatite samples were synthesized by wet chemical method and characterized by X-ray Fluorescence Spectrometry, X-ray Diffraction, Fourier Transformed Infrared Spectroscopy and High Resolution Transmission Electron Microscopy. The XRD and FTIR analysis confirmed the presence of one B-type carbonate apatite phase and the HRTEM images revealed the coexistence of amorphous and polycrystalline regions in the order of 2nm with the carbonate apatite structure. Second phases or precursors were not discovered.

Abstract: The bioceramics nanostructured have made important characteristics in biomedical applications, especially the calcium phosphate ceramics. The aim of this work is synthesis and characterization of calcium phosphate and nanocomposites powders, the method of dissolution of CaO in liquid medium, precipitation and formation of bone calcium phosphate matrix, and nanocomposites by adding the solution of phosphoric acid (H3PO4). The nanocomposites powders were synthesized using as strengthening silica gel nanometer (20nm) at concentrations of 1%, 2%, 3% and 5% by volume and subjected to heat treatment to 900°C for 2 hours, seeking obtained HA (Hydroxyapatite). Later the bone matrix of calcium phosphate and nanocomposites powders were subjected from process attrition milling for 2 hours, by way of comparison. The studies characterizations were conducted through the technique of X-ray diffraction, scanning electron microscopy (SEM) and dilatometric test.

Abstract: In the last decades many investigations have been oriented toward the development of nanostructured biomaterials such as calcium phosphate ceramics, particularly those composed of stoicheiometric hydroxyapatite (Ca10(PO4)6(OH)2) and a-and β- tricalcium phosphate (Ca3(PO4)2), which present chemical and crystallographic similarities with hard tissues (bones and teeth). Because of these characteristics, these materials can be used for reconstitution and regeneration of bone tissues. The odontological and biomedical applications are still limited due to their brittle behaviour. This study was focused in the synthesis and characterization of a bone matrix of calcium phosphate (β-TCP) and hydroxyapatite (HAP-101 e HAp-201). The results presented here are related to the morphological characterization of nanostructured powders from scanning electron microscopy viewpoint. X-ray diffraction was used to identifier the present phases in the powders and the infrared spectrometry (FTIR) was used to analyse OH bonds from hydroxyapatite and PO4 from calcium phosphates.