Abstract The aim of this work was to use the Washburn capillary rise method to evaluate changes in surface energy promoted by the insertion of CuO in a 58S glass and its implication in bioactivity. The presence of CuO decreased the surface wettability by decreasing the Lewis acid-base component γSAB and increasing the Lifshitz-van der Waals component γSLW. The insertion of CuO also diminished the value of the electron donor parameter γS-; i.e., the number of negative groups. This was accompanied by a nonuniform apatite formation on the surface, likely because the presence of CuO-rich regions with lower electron donor values impaired the adsorption of Ca2+, preventing uniform apatite precipitation. Therefore, surface energy was extremely sensitive to small physical and chemical changes in the glass structure and the behavior of the electron donor parameter could be used as an adequate probe to predict glass bioactivity.

Ionic trace elements such as Mg2+, Mn2+ and Sr2+ are very difficult to stabilize in the hydroxyapatite lattice, and they can induce phase transformations when subjected to thermal treatments. The effects of the ions themselves are often confused with the effects of the newly formed phases. Therefore, the objective of this work was to evaluate the effects of the ions isolated from the effects caused by the inherent phase transformations observed in these systems. WDXRF, XRD, FTIR and biological assays using mouse preosteoblastic cells (MC3T3-E1) showed the Mg2+ ions can stimulate cell differentiation even when segregated from the HA structure in the form of MgO. However, the presence of MgO considerably retards cell proliferation. At the same time, Mn2+ ions are able to increase cell proliferation and induce the production of high levels of ALP, regardless of whether they are inserted into the HA structure or segregated in the form of Mn3O4. Finally, the presence of Sr2+ in the HA lattice does not appear to directly affect cell behavior, since both the proliferation and production of ALP are comparable to those observed in the nondoped HA sample.

Bioceramics synthesized in laboratories must undergo biological tests that consider the final format and all the processing steps involved in the production of the final device. However, in many cases, the synthesized materials are characterized in formats very different from those that will ultimately be implanted into the body. Once living cells are directly cultured on surfaces, a mismatch between bulk and surface microstructural characterizations often leads to the misinterpretation of biological responses. Therefore, our objective in this work was to determine whether and at what level significant microstructural changes can occur between the surface and the bulk of hydroxyapatite pellets produced by uniaxial pressing followed by calcination. Our results showed that the as-synthesized hydroxyapatite crystals had a preferential orientation along the [0 0 1] direction. The calcination process followed by grain growth inhibited this texture feature. However, on the pellet surfaces, the initial orientation was preserved. At the same time, crystallite growth was inhibited, and the cell unit volume of the crystals on the surface was significantly lower than that of the crystals in the bulk. These results demonstrated that the crystallographic features on the surface of hydroxyapatite pellets can be completely different from those observed for the bulk.

The objective of this study was to evaluate how silver can be inserted into hydroxyapatite (HA) via two distinct processes: co-doping with CO32- via precipitation in an aqueous medium and immersion of preformed HA crystals into Ag+ solutions. It was concluded that although Ag+ and Ca2+ have different radii, the accommodation of Ag+ ions in the Ca2+ sites of the hydroxyapatite lattice can be explained by the models proposed for inserting monovalent ions such as Na+. In this case, because Ag+ ions are larger than Ca2+ ions and have a different charge, the Ag+ ions are stabilized in the HA structure by co-substitution with CO32- ions in both the A- and B-type sites. This simultaneous insertion of Ag+ and CO32- appears to thermally stabilize the HA phase because no phase transformation is observed after calcination. In addition, the doping of HA with Ag+ ions can clearly occur via two routes: co-precipitation in the presence of these ions or diffusion in preformed hydroxyapatite crystals. This result appears to indicate the possibility of doping HA with Ag+ using less complex routes at ambient temperature and with prefabricated implants or biomaterials, which reduces the costs of producing devices with antibacterial effects.