Possibilities of Mechanochemical Synthesis of Apatites with Different Ca/P Ratios

Abstract

Apatite is widely used in medicine as a biomaterial for bone tissue restoration. Properties of apatite depend on its composition, including the Ca/P ratio. This paper shows what range of Ca/P ratio can be attained in apatite by the mechanochemical method of synthesis, providing fast formation of a single-phase product. The synthesis was carried out from a reaction mixture of CaHPO4 and CaO at different Ca/P ratios in the range of 1.17–2.10. The products were studied by PXRD, FTIR and NMR spectroscopy, HRTEM, and STA. In mixtures with a low initial Ca/P ratio (1.17–1.48), directly in the mill, the formation of calcium orthophosphate with whitlockite structure containing an HPO42− group and structural water is shown for the first time. This phosphate has structure similar to that of whitlockites of hydrothermal origin and differs from high-temperature β-tricalcium phosphate that has composition Ca3(PO4)3. A series of samples of apatite was obtained with varied composition, which depends on the initial Ca/P ratio. At Ca/P < 1.67, the formation of two types of calcium-deficient apatite was documented. At Ca/P > 1.67, the existence of two types of calcium-rich apatite is confirmed.

Hydrolytic Degradation and Bioactivity of Electrospun PCL-Mg-NPs Fibrous Mats

“…ePCL+ MgO 10 wt% presented a Ca/P ratio of 1.17, which can be reconducted to the formation of two possible products, namely dicalcium phosphate or Brushite with the chemical formula CaHPO 4 and the β-form of tricalcium phosphate Ca 3 (PO 4 ) 2 [ 47 , 48 ].…”

“…In fact, all the samples showed new signals due to the degradation process: one broad peak at 3400 cm −1 related to the -OH stretching vibrations, and another signal around 1630 cm −1 that can be attributed to the carboxyl groups formed after the degradation [ 32 ]. Furthermore, after 28 days, the signals related to the growth of calcium apatite can be seen: in particular, two new sharp peaks at 596 cm −1 and 660 cm −1 that can be attributed to the bending vibrations of PO 4 3− and another signal at 909 cm −1 of the HPO 4 2− group [ 48 ]. Another relevant signal appeared at 1628 cm −1 that is attributed to hydroxyl liberation mode, and another peak at 1550 cm −1 is indicative of the vibrations of CO 3 2− [ 50 , 51 ].…”

Hydroxyapatite Double Substituted with Zinc and Silicate Ions: Possibility of Mechanochemical Synthesis and In Vitro Properties

“…It is possible that at x = 2, there is more water than is involved in the hydroxide formation. Water molecules present in the reaction mixture can be both sorbed by the surface of the particles and incorporated into the HA crystal lattice [ 21 , 22 ]. According to Table 1 , at x = 2, apatite with composition Ca 8.0 Zn 2.0 (PO 4 ) 4.0 (SiO 4 ) 2.0 should crystallize.…”

“…Although the XRD data indicated the presence of a large amount of an amorphous phase in the 2.0-ZnSi-HA sample, HRTEM showed that all particles were crystalline. This discrepancy can be explained by the fact that amorphous calcium phosphates are prone to crystallization under an electron beam due to intensive heating during HRTEM measurements [ 22 ]. Figure 6 shows that the distribution of the elements in the particles of 2.0-ZnSi-HA was uniform.…”

Effect of calcination on physicochemical and biological properties of ion-modified nanohydroxyapatite for bone tissue engineering applications

“…On the other hand, better bioactivity can be achieved when the ratio < 1.67 [8,9]. Hydroxyapatite can also be carbonated, and depending on the position of the carbonate group in the structure, various types of HAP can be distinguished, namely, HAP type A, with substituted hydroxide ions, HAP type B, with substituted phosphate ions, and a mixed AB type [10]. However, numerous scienti c studies prove that HAP type B is essential for bone regeneration because it is similar to biological apatite [11].…”