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    Co-doped hydroxyapatites as potential materials for biomedical applications
    (Elsevier Science Bv, 2019) Yilmaz, Bengi; Alshemary, Ammar Z.; Evis, Zafer
    Hydroxyapatite (HA) is a synthetic biomaterial resembling the composition of mammalian hard tissue and thus, it is widely employed as a bone graft material, hard tissue engineering scaffold and coating layer for metallic substrates. Biological apatite is non-stoichiometric in nature. It is composed of small crystals and characterized by poor crystallinity and relatively high solubility with respect to stoichiometric HA. Chemical compositions of these crystals consist of Ca, P and trace amounts of various ions, such as Mg2+, Zn2+, Sr2+, Ag+, Cl- and F- which are more prominent as dopants or adsorbed on the crystal surface. However, these ions play an important role in the metabolism of hard tissues. Synthetic HA is a stoichiometric material with a Ca/P ratio of 1.67, which lacks the presence of valuable trace ions regularly present in natural hard tissue. Thus, the structure of synthetic HA is partially incorporated by these ions to mimic the chemical composition of the biological apatite structure. Ionic substitutions have been planned as a tool to enhance the biological role of HA based materials. As single dopant frameworks have indicated great outcomes, it makes sense that various dopants can be utilized to further build the valuable impacts of each, within the constraints of the material stability of HA. This review is focused on co-ionic substitutions in HA system and their combined effects on related biomedical characteristics.
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    Strontium and fluorine co-doped biphasic calcium phosphate: characterization and in vitro cytocompatibility analysis
    (Iop Publishing Ltd, 2017) Pourreza, Elmira; Alshemary, Ammar Z.; Yilmaz, Bengi; Rad, Reza Moonesi; Tezcaner, Aysen; Evis, Zafer
    Strontium (Sr2+) and fluoride (F-) ions are known to play an important role in bone and tooth metabolism. In this work, we prepare biphasic calcium phosphate (BCP) bioceramics co-doped with different fractions of Sr2+ and F- ions to investigate the impact of dopant on the crystal structure and biological properties of BCP bioceramics. The materials were successfully synthesized using a wet precipitation method, followed by sintering at 1100 degrees C for 1 h. The sintered materials were characterized using x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). XRD analysis revealed that the BCP bioceramics were composed of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), along with calcium oxide (CaO) as impurity. Furthermore, the percentage of beta-TCP tended to increase with an increase in the Sr2+ ion concentration. The lattice parameters of HA phase expanded along with incorporation of Sr2+ and F- ions. The morphology of the yielding materials demonstrated that the incorporation of Sr2+ and F- ions caused a decrease in the grain size. The Vickers hardness (HV) test showed that hardness values increased with increasing Sr2+ concentrations. In vitro cell culture tests were performed with human osteogenic sarcoma (Saos-2) cell line. Saos-2 cells attached and proliferated faster on Sr/F-BCP materials compared to pure BCP, showing that Sr/F-BCP materials were cytocompatible.
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    Synthesis and sintering of B, Sr, Mg multi-doped hydroxyapatites: Structural, mechanical and biological characterization
    (Elsevier, 2021) Yedekci, Busra; Tezcaner, Aysen; Alshemary, Ammar Z.; Yilmaz, Bengi; Demir, Teyfik; Evis, Zafer
    Hydroxyapatite (HA, Ca-10(PO4)(6)(OH)(2)) is the main constituent mineral of bone and teeth in mammals. Due to its outstanding biocompatibility and osteoconductive capabilities, it is preferred for bone repair and replacement. Owing to high potential to have excellent biological properties, ternary ions-doped HAs have just begun to be investigated in the biomedical field and preparing multi-doped HAs is a fairly new approach. Boron (B, BO33-), strontium (Sr, Sr2+) and magnesium (Mg, Mg2+) provide a beneficial effect on bone growth, bone strength, biocompatibility and positively affect bone microstructure. The motivation of this study is taking advantages of the potential of the combine effects of these bivalent ions. In this study, 8 different compositions of BO33- , Sr2+, Mg2+ multi-doped HAs were synthesized by microwave irradiation method to investigate the structural, mechanical and biological features of bone substitutes. This is the first time we report the effect of boron, strontium and magnesium ions multi-doping on the structure of HA and its biological properties. Samples were sintered at 700, 900 and 1100 degrees C. The effect of varying ion contents and sintering temperature on structural and biological properties of the multi-doped samples was investigated. B, Sr and Mg ions were successfully doped into the HA structure according to X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analyses. A biphasic structure was obtained with increasing amount of ion-doping. Increasing the sintering temperature affected the crystallinity and the density of the samples gradually. Vicker's microhardness and diametral strength of the samples increased at high sintering temperatures. B-Sr-Mg multi-doped HA promoted osteoblast-like Saos-2 cell proliferation, and as the sintering temperatures of the samples increased, the osteogenic differentiation level of the cultured cells also increased. Overall, results showed that the biological properties of HA were improved with the doping of Sr, Mg and B ions, and for bone implant applications samples sintered at 1100 degrees C were suggested to have potential as a biomaterial.