The effects of Zn and Sr Co-doping on local structure, dielectric properties, and bioactivity of hydroxyapatite porous materials

Hydroxyapatite (HA) is a vital biomaterial widely used in bone implants and orthodontics due to its excellent biocompatibility. In this study, Sr and Zn co-doped HA was synthesized using the sol-gel combustion method and cast into porous materials. Samples containing 5 mol% Sr and varying Zn concentrations (0, 1, 3, and 5 mol%) were labeled as 0ZnSr-HA, 1ZnSr-HA, 3ZnSr-HA, and 5ZnSr-HA, respectively. The crystal and local structures were analyzed using X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES), revealing that Zn²⁺ and Sr²⁺ ions substitute at the Ca1 and Ca2 sites within the hydroxyapatite lattice. The dielectric properties were investigated over a frequency range of 20–10³ Hz, where 3ZnSr-HA exhibited the highest dielectric constant of 39.74, suggesting its potential to support bone growth during simulated body fluid (SBF) testing. The microstructure and elemental composition of the samples were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). After 2 weeks of immersion in SBF, 3ZnSr-HA demonstrated significant apatite growth, highlighting the ability of Zn and Sr co-substitution to enhance the HA structure and improve bone regeneration efficiency. This study confirms the potential of Sr- and Zn-doped HA as a promising material for biomedical applications.