F. Miculescu, A. Maidaniuc, S.I. Voicu, M. Miculescu, D. Batalu
University Politehnica from Bucharest, Romania
pp. 31 - 34
Keywords: bovine bone-derived materials, thermal processing, ceramic particle processing and optimization
In this abstract we propose the strategies optimization for obtaining ceramic materials derived from natural sources for solid free-form fabrication, used for bone substitution. The selected method, thermal processing, is simple (due to the similarities between the raw material and the bone), economic (it is based on parameters control of some traditional processing methods), environmental safe (the raw material comes from other production processes) and biological hazards free (if the heat treatment is performed at high temperatures). The main objectives are the assessment of the changes induced by the thermal processing control of bovine bone tissue and the complex evaluation of the obtained products. For this study, bovine bone was selected as raw material. The heat treatment parameters setup was made following a preliminary study in which results on thermogravimetric analysis (TGA) and the DSC in air and argon atmosphere, were obtained. Ceramic materials derived from natural sources were produced by heat treatments at temperatures between 1000 and 1200°C, by varying the heat treatment environment and cooling conditions. The influence of the heat treatment parameters variations was evaluated in terms of morphology (by scanning electron microscopy - SEM) and composition (by Fourier Transform Infrared Spectroscopy - FT-IR). The processing of materials derived from bovine bone continued with grinding of the products previously obtained and with their size sorting, in order to assess the characteristics of obtained powders by the particle size. The processing method permitted the obtaining of different batches of material with different particle sizes, compositions and structures. The application of heat treatment at temperatures above 1000°C induced the apparition of hydroxyapatite crystals with granular morphology, embedded in a porous architecture. Increasing the temperature at 1100-1200°C, the porosity is reduced due to a microstructure densification process. The transformation of hydroxyapatite in β-TCP was not observed in TGA-DSC analysis made in air atmosphere, the differences being assigned to the chemical composition of bone that influence the transformation of the biological hydroxyapatite into β-TCP. Obtaining of products with tuned phasic composition was accelerated by bone heat processing in argon atmosphere. Partial conversion of the hydroxyapatite into β-TCP was identified in the 850 - 1200°C temperature range with a exothermic peak near 1000°C. The beginning of a new thermal event can be identified starting from 1200°C, suggesting the conversion of β-TCP into alpha-tricalcium phosphate (α-TCP) (which theoretically occurs at temperatures above 1125°C). However the change of cooling conditions influences the characteristics of the bovine bone treated at high temperatures. The FT-IR analysis shows characteristic peaks with low intensities for the samples rapidly cooled in water, regardless of the heat treatment temperature. The microstructure densification is accentuated when cooling in frozen water.