Tuning the Properties of Hydroxyapatite through Mg/Zn Co-Doping: A Pathway to Advanced Biomedical Devices

The aim of this study is to explore the potential of Mg/Zn-codoped hydroxyapatite as bioelectrets and electro-active scaffolds for tissue engineering and implantable devices. This study investigates the structural, electrical, and biological properties of Mg/Zn codoped hydroxyapatite (Ca_10-x-yZn_xMg_y(PO₄)₆(OH)₂; where x = y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0.) ceramics, synthesized via the solid-state reaction method. Structural analysis confirmed that the hydroxyapatite phase was retained at lower doping levels (x = y ≤ 0.4), while a tricalcium phosphate (TCP) secondary phase emerged at higher concentrations (x = y ≥ 0.6). This structural transition influences the mechanical integrity and bioactivity of the material. Dielectric properties showed a dielectric constant ranging from 8.08 to 13.17 (at 1 MHz and 310 K), correlating with increased grain size and reduced grain boundary resistance. These findings highlight the material's potential for charge storage applications, which are crucial for bioelectric-based devices. Electrical conductivity analysis revealed AC conductivity values of 10^-7-10^-6 S/cm, with activation energy decreasing from 0.24 to 0.10 eV at higher doping levels, indicating improved charge carrier mobility. Enhanced conductivity is beneficial for electro-active scaffolds facilitating cellular stimulation. Biocompatibility of the material was evaluated using the MTT assay on normal human skin keratinocytes (PSVK-1) and lung fibroblasts (Wi-38), both of which exhibited no cell cytotoxicity, establishing the material's cytocompatibility for biomedical applications. Protein adsorption studies using bovine serum albumin (BSA) peaked at 21.22 μg/mL for x = y = 0.4, attributed to favorable electrostatic interactions. The least negative zeta potential (-31.3 mV at x = y = 0.4) enhanced colloidal stability and protein adhesion, which is crucial for biomaterial integration in tissue engineering. These combined properties of structural stability, enhanced conductivity, favorable dielectric response, and high biocompatibility demonstrate that Mg/Zn codoped hydroxyapatite is a promising material for bone tissue engineering, bioelectrets for advanced medical devices, and electro-active scaffolds and coatings for implants.