Synthesis and characterization of Sr and Mg-doped hydroxyapatite by a simple precipitation method

Abstract

This study presents the preparation of pure, Sr and Mg-doped hydroxyapatite (HAP) by precipitation. Sr-doped HAPs (SrHAPs) and Mg-doped HAPs (MgHAPs) were fabricated with Sr molar ratio of 2, 4, 6, 8, 12 % and Mg molar ratio of 2, 4 %, respectively. Ca(NO3)2, Sr(NO3)2, Mg(NO3)2, (NH4)2HPO4 were used as starting materials, the Ca/P molar ratio was kept 1.67 during every synthesis and a 900 °C heat treatment was conducted to enhance the crystallinity. All of the products were analyzed by XRD, SEM and EDX, moreover lattice parameters and crystallite size calculations were performed to prove the ion incorporation into the crystal structure. The HAP structure was maintained when 2 and 4 Sr and 2 Mg % were applied and EDX confirmed the Sr and Mg content in these samples. In all other cases, various Sr and Mg-containing phases (Sr0.13Ca2.87(PO4)2, Ca2P2O7, Mg0.29Ca2.71(PO4)2) were identified while the HAP structure disappeared. It was shown that lattice parameters and the unit cell volume of Sr-doped HAPs increased slightly compared to pure HAP due to the bigger radius of Sr 2+ than Ca 2+. As the ionic radius of Mg 2+ is smaller than Ca 2+ , we demonstrated the distortion in the unit cell. Crystallite sizes increased as the amount of Sr and Mg raised. SEM experiments demonstrated that ion incorporation had little influence on the morphology, i.e. pure, Sr or Mg-doped HAPs were mostly homogenous, constituted of strongly sintered nanometer sized grains. Antimicrobial tests indicated that SrHAP with 4 Sr % and MgHAP with 2 % Mg had positive effect on cell viability.

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

“…The obtained nanocrystals expected stoichiometry has been established supposing that doping elements entered the HA cells by substituting calcium cations (Bigi et al, 1993;Bigi et al, 1996;Bigi et al, 2007;Nagyné-Kovács et al, 2018;Pan et al, 2009). The obtained nanocrystals expected stoichiometry has been established supposing that doping elements entered the HA cells by substituting calcium cations (Bigi et al, 1993;Bigi et al, 1996;Bigi et al, 2007;Nagyné-Kovács et al, 2018;Pan et al, 2009).…”

“…we prepared 0.5% Mg doped HA and 0.5% and 1% Mg-Sr doped HA, labeled respectively as HAMg0.5, HAMgSr0.5 and HAMgSr1. Taking into account the charge balance and according to the literature (Bigi et al, 1993;Bigi et al, 1996;Bigi et al, 2007;Nagyné-Kovács et al, 2018;Pan et al, 2009), we can assume that the cation substituent enters the HA cell substituting calcium. As a consequence of this consideration we subtracted from the stoichiometric amount of calcium the same molar amount of substituent, in order to keep the ratio (Ca + Mg + Sr)/ P = 1.67, as summarized in The reaction mixture was kept under stirring (always at 70 C) overnight, and the precipitated was then left for 2 hr at room temperature to allow the deposition of the inorganic phase, before being filtered and washed using milliQ water.…”

“…Nagyné-Kovács et al (2018) have prepared Sr-and Mg-doped hydroxyapatite with high molar ratio (i.e., Sr/(Ca + Sr) and Mg/(Ca + Mg)) of these ions, respectively 2, 4, 6, 8 and 12%, and 2% and 4%. With this rationale, recently the behavior of Sr and Mg doped HA crystals upon thermal treatments have been investigated.…”

“…With this rationale, recently the behavior of Sr and Mg doped HA crystals upon thermal treatments have been investigated. Nagyné-Kovács et al (2018) have prepared Sr-and Mg-doped hydroxyapatite with high molar ratio (i.e., Sr/(Ca + Sr) and Mg/(Ca + Mg)) of these ions, respectively 2, 4, 6, 8 and 12%, and 2% and 4%.…”

Hydrothermal Synthesis of Sr-doped Hydroxyapatite and Its Antibacterial Activity

“…During metal ion incorporations mainly Ca 2+ is replaced by Mg 2+ , Zn 2+ , Sr 2+ and Ag + . With the usage of Ag the antibacterial activity and non-cytotoxicity increase significantly [9,14,15], Mg, Zn and Sr can induce greater osteoconductivity, cytotoxibility or even antimicrobial effect, but Sr can also promote sustained drug release [13,[16][17][18][19][20][21][22][23]. The replacement of Ca 2+ by another ion modifies the crystal structure by causing unit cell contraction or expansion depending on the ionic radii, but also has influence on the crystallinity, crystallite size, morphology, surface charge and solubility.…”