Insert Figure 2.5 Characterization In this step, hydroxyapatite nanoparticle samples were selected for characterization. For x-ray diffraction and FTIR all hydroxyapatite nanoparticles samples obtained according to 2 3 factorial designs were characterized. However, for TEM analysis the samples H2-EN, H2-C-EN, H5, H5-C, H8-EN, H8-C-EN, H9-EN, and H9-C-EN were characterized. The choice of these samples is result of 2 3 design that showed that the chosen variables did not affect the crystallite size of hydroxyapatite (Table ).