Structure of biomimetic apatite grown on hydroxyapatite (HA)

Nanocrystalline hydroxyapatite (HA) is the bone mineral phase in vertebrate animals. When bones suffer illness or injuries, natural hydroxyapatite reconstructs and remodels its structure. It has been demonstrated that synthetic hydroxyapatite materials emulate bone properties and enhance bone-bonding ability through a biomimetic apatite coating, obtained when bioactive materials are immersed in a physiological-like media. In this research, the biomimetic apatite structure deposited in three synthetic hydroxyapatites (HAs: HA_MS, HA_UB, and HA_UT), after being immersed in a simulated body fluid (SBF), is studied. The synthetic HAs are obtained by co-precipitation, using three different stirring methods: magnetic stirring (HA_MS), ultrasonic bath (HA_UB), and ultrasonic tip (HA_UT). The synthetic HAs are characterized by X-Ray Diffraction (X-RD), High-Resolution Scanning Electron Microscopy (HR-SEM), Energy Dispersive X-ray (EDX) microanalysis and Transmission Electron Microscopy (TEM) before and after SBF assays. The crystal sizes of synthetic HAs are 12.567 nm, 15.188 nm, and 17.903 nm for HA_MS, HA_UB, and HA_UT, respectively. Additionally, HAs have values between 0.940 and 0.942 nm for a-cell parameter, and values between 0.688 and 0.689 nm for c-cell parameter. After 28 days of immersion in Simulated Body Fluid (SBF), the materials show poor crystalline-fine films of biomimetic apatite covering their surfaces. These biomimetic apatite films have values between 0.946 and 0.969 nm for the a-cell parameter and values between 0.698 and 0.710 nm for the c-cell parameter. Hence, crystallinity, crystal size, and morphology of synthetic HAs are dependent on the stirring method used during the synthesis process, which affects the structural characteristics of the biomimetic apatite layers deposited on the synthetic HAs surfaces.