Hydrothermal Synthesis of Sr-doped Hydroxyapatite and Its Antibacterial Activity

Abstract

In this study, we prepared hydroxyapatite (HAP) samples using hydrothermal method. We investigated the effect of reaction conditions such as phosphate excess applying 1.49 and 1.67 (as stoichiometric) Ca/P ratio, pH (9/ 10/ 11/ 12) and time (4/ 8/ 12/ 24 h). Sample characterization was carried out by XRD and SEM. The results showed, all samples had HAP structure, however, lower Ca/P ratio, larger reaction time and setting the pH to 10 increased the crystallinity. Then, we synthetized Sr-doped HAP samples, varying the Sr concentration using 2, 4, 6, 8 and 10 % Sr/ (Ca+Sr). The Sr content was revealed by EDX. Sr-incorporation did not change the obtained crystalline HAP phase but the unit cell parameters increased. We calculated lattice constants and found that a, b changed from 9.4310 Å to 9.4700 Å, c from 6.8819 Å to 6.9227 Å and the unit cell volume from 530.0951 Å3 to 537.6556 Å3 due to the larger ionic radius of Sr compared to Ca. The pure and doped samples had uniform, mostly needle-like morphology with 100-300 nm length and 25-100 nm. In vitro cytotoxicity tests revealed evident antibacterial activity in the case of doped samples compared to pure HAP against E. coli.

Anisotropic expansion effect of Sr doping on the crystal structure of hydroxyapatite

“…The substitution position of Sr in HA may depend on the synthesis method of the materials. Various synthesis methods of Sr-doped HA have been developed such as chemical precipitation, 23 hydrothermal methods, 24,25 sol-gel routes, 26 etc. These methods usually start with soluble salts as Ca, Sr, and P sources, and the pH environment is adjusted to alkaline conditions to make the Ca and Sr ions homogeneously precipitate into HA.…”

Probing the influence of strontium doping and annealing temperature on the structure and biocompatibility of hydroxyapatite nanorods

“…Different morphologies, mechanical properties, levels of crystallinity, and stoichiometries can be achieved for HAp based on the method employed. 25 Nagyné-Kovács et al have synthesized needle-shaped HAp and Sr-HAp via the hydrothermal method which showed excellent antibacterial activity; 26 Ehret et al have synthesized Sr-HAp via the chemical precipitation method for enhanced bioactivity. 27 Porous microspherical Sr-HAp was prepared by Lin et al using a surfactant-free hydrothermal technique for bone regeneration and drug delivery application.…”

Zn-doped mesoporous hydroxyapatites and their antimicrobial properties

“…Both inorganic and organic materials and their combinations have been used as antimicrobial agents against gram-positive and gram-negative bacteria. Among the various antimicrobial inorganic materials investigated till date, oxides such as titanium oxide [2,3], silver oxide [4], and zinc oxide [5][6][7] and phosphates such as pure hydroxyapatite (HAp) [8], HAp doped with different cations including zinc [9], silver [10][11][12], cerium [13,14], strontium [15], copper [16], and titanium [17] have been extensively investigated.…”