Synthesis and characterisation of nanophase hydroxyapatite co-substituted with strontium and zinc

Abstract

In order to develop new bioactive calcium phosphate (CaP) materials to repair bone defects, it is important to ensure these materials more closely mimic the non-stoichiometric nature of biological hydroxyapatite (HA). Typically, biological HA combines various CaP phases with different impurity ions, which substitute within the HA lattice, including strontium (Sr 2+), zinc (Zn 2+), magnesium (Mg 2+), carbonate (CO 3 2-) and fluoride (F-), but to name a few. In addition to this biological HA have dimensions in the nanometre (nm) range, usually 60 nm in length by 5-20 nm wide. Both the effects of ion substitution and the nano-size crystals are seen as important factors for enhancing their potential biofunctionality. The driving hypothesis was to successfully synthesise nanoscale hydroxyapatite (nHA), co-substituted with strontium (Sr 2+) and zinc (Zn 2+) ions in varying concentrations using an aqueous precipitation method and to understand their chemical and physical properties. The materials were characterised using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) techniques. The FTIR, XRD and XPS results confirmed that the nHA was successfully co-substituted with Sr 2+ and Zn 2+ , replacing Ca 2+ within the nHA lattice at varying concentrations. The FTIR results confirmed that all of the samples were carbonated, with a significant loss of hydroxylation as a consequence of the incorporation of Sr 2+ and Zn 2+ into the nHA lattice. The TEM results showed that each sample produced was nano-sized, with the Sr/Zn-10% nHA having the smallest sized crystals approximately 17.6 ± 3.3 nm long and 10.2 ± 1.4 nm wide. None of the materials synthesised here in this study contained any other impurity CaP phases. Therefore, this study has shown that co-substituted nHA can be prepared, and that the degree of substitution (and the substituting ion) can have a profound effect on the attendant materials' properties.

Sintering of magnesium‐strontium doped hydroxyapatite nanocrystals: Towards the production of 3D biomimetic bone scaffolds

“…Substitution of Sr 2+ ions at Ca 2+ sites in HA lattice is well reported (Frasnelli et al, 2017;Lowry et al, 2018;Šupovà, 2015;Terra et al, 2009). Substitution of Sr 2+ ions at Ca 2+ sites in HA lattice is well reported (Frasnelli et al, 2017;Lowry et al, 2018;Šupovà, 2015;Terra et al, 2009).…”

“…Another essential element in bone structure is Sr. Substitution of Sr 2+ ions at Ca 2+ sites in HA lattice is well reported (Frasnelli et al, 2017;Lowry et al, 2018;Šupovà, 2015;Terra et al, 2009). It exhibits a bone-seeking behavior and replaces Ca in the osteoblast activity.…”

Double Substituted Carbonated Hydroxyapatite for Stone Consolidation

“…), B-CHAp (by replacing the OH -), or AB-CHAp can be obtained. In some application, osteoinductivity and antimicrobial properties can be obtained by the insertion into the structure of metallic ions, like Sr 2+ and Zn 2+ , by replacing Ca 2+ from CHAp [5,9,10].…”

Multisubstituted hydroxyapatite powders and coatings: The influence of the codoping on the hydroxyapatite performances

“…Dual ionic substitutions can be considered as a promising strategy to improve the physicochemical and biological properties of HAp. Mostly, both of the two considered vicarious ions are cations, whereas in some cases the anion/anion and anion/cation combinations were investigated. As expected, HAp gets different physico‐chemical properties and biological performances on the basis of the vicarious ions kinds and amounts.…”

“…Lowry et al also synthesised Sr 2+ /Zn 2+ co‐substituted nHAp (Sr/Zn‐2.5%nHAp, Sr/Zn‐5%nHAp and Sr/Zn‐10%nHAp) by wet precipitation, comparing them with undoped nano‐hydroxyapatite and monosubstituted HAp (Sr‐substituted nHAp [Sr10%nHAp] and Zn‐substituted nHAp [Zn10%nHAp]). The obtained powders were composed of carbonated hydroxyapatite with a significant loss of hydroxylation as a consequence of Sr/Zn co‐doping.…”