Browsing by Author "Martins, G"
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- Effect of the calcination temperature on the composition and microstructure of hydroxyapatite derived from human and animal bonePublication . Figueiredo, M; Fernandes, A; Martins, G; Freitas, J; Judas, F; Figueiredo, HThe present work focus the study of cortical bone samples of different origins (human and animal) subjected to different calcination temperatures (600, 900 and 1200 °C) with regard to their chemical and structural properties. For that, not only standard techniques such as thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used but also mercury intrusion porosimetry. The latter technique was applied to evaluate the effects of the temperature on the microstructure of the calcined samples regarding porosity and pore size distribution. Although marked alterations in structure and mineralogy of the bone samples on heating were detected, these alterations were similar for each specimen. At 600 °C the organic component was removed and a carbonate apatite was obtained. At 900 °C, carbonate was no longer detected and traces of CaO were found at 1200 °C. Crystallinity degree and crystallite size progressively increased with the calcination temperature, contrary to porosity that strongly decreased at elevated temperatures. In fact, relatively to the control samples, a significant increase in porosity was found in samples calcined at 600 °C (reaching values around 50%). At higher temperatures, a dramatic decrease was observed, reaching, at 1200 °C, values comparable to those of the non-calcined bone
- Evaluating structural differences in cortical bone tissue after demineralization and calcinationPublication . Martins, G; Freitas, J; Judas, F; Trindade, B; Figueiredo, HAlthough the best results in bone grafting have been achieved with autogeneuos bone tissue, allografts and xenografts have been widely used either in mineralized, demineralized, or calcined forms. Demineralized bone has been proven to stimulate new bone formation by exposing, proteins and growth factors necessary for osteoinduction. On the other hand, calcined bone offers a natural architectural mineralized matrix, not present in synthetic apatite materials, as well as an excellent source of calcium. Despite the extensive use and importance of these materials, systematic works regarding their characterization are relatively scarce.
- Influence of hydrochloric acid concentration on the demineralization of cortical bonePublication . Figueiredo, M; Cunha, S; Martins, G; Freitas, J; Judas, F; Figueiredo, GAlthough demineralized bone matrix has been considered a successful grafting material, combining both osteoconductive and osteoinductive properties, conflicting results have been published in the literature regarding its bone-inducing abilities. This may be a consequence of following different demineralization procedures that naturally result in products with different properties. The present work examines the evaluation of the demineralization process of similar samples of human cortical bone using three different concentrations of hydrochloric acid solutions (0.6 M, 1.2 M and 2.4 M). Sample calcium content was determined (by Atomic Absorption Spectroscopy) at various immersion times, allowing the construction of the corresponding kinetic profiles. Phase and chemical composition were enabled by X-Ray Diffraction Spectroscopy and Fourier Transform Infrared Analysis, respectively. Structural modifications were followed by Light and Scanning Electron Microscopy and quantified by mercury porosimetry (in terms of porosity and pore size distribution). As expected, increasing the acid concentration led to an increase in the demineralization rate, but not in a proportional way. However, one of the most significant effects of the acid concentration was found on the sample structural features. In fact, a considerable increment in porosity was detected for the sample subjected to the highest hydrochloric acid concentration. Microscopic observations demonstrated that despite the structural deformation resultant from demineralization, the basic microstructure was preserved.
- Physicochemical characterization of biomaterials commonly used in dentistry as bone substitutes--comparison with human bonePublication . Figueiredo, M; Henriques, J; Martins, G; Guerra, F; Judas, F; Figueiredo, HThe present work focuses on the physicochemical characterization of selected mineral-based biomaterials that are frequently used in dental applications. The selected materials are commercially available as granules from different biological origins: bovine, porcine, and coralline. Natural and calcined human bone were used for comparison purposes. Besides a classical rationalization of chemical composition and crystallinity, a major emphasis was placed on the measurement of various morphostructural properties such as particle size, porosity, density, and specific surface area. Such properties are crucial to acquiring a full interpretation of the in vivo performance. The studied samples exhibited distinct particle sizes (between 200 and 1000 microm) and shapes. Mercury intrusion revealed not only that the total sample porosity varied considerably (33% for OsteoBiol, 50% for PepGen P-15, and 60% for BioOss) but also that a significant percentage of that porosity corresponded to submicron pores. Biocoral was not analyzed by this technique as it possesses larger pores than those of the porosimeter upper limit. The density values determined for the calcined samples were close to the theoretical values of hydroxyapatite. However, the values for the collagenated samples were lower, in accordance with their lower mineral content. The specific surface areas ranged from less than 1 m(2)/g (Biocoral) up to 60 m(2)/g (BioOss). The chemical and phase composition of most of the samples, the exception being Biocoral (aragonite), were hydroxyapatite based. Nonetheless, the samples exhibited different organic material content as a consequence of the distinct heat treatments that each had received.