Multifunctional Characteristics of Cu/Zn Co-Doped Hydroxyapatite: Enhanced Electrical, Surface, and Biocompatibility

Abstract

Developing multifunctional biomaterials with both electrical and biological properties is crucial for next-generation biomedical platforms. This study looks into how Cu/Zn co-doping affects the structural, electrical, and biological performance of hydroxyapatite (Ca_10-x-yZn_xCu_y(PO₄)₆(OH)₂; x = y = 0.2–1.2), which was synthesized through a solid-state reaction. Among the samples, the CZ6 composition (x = y = 0.6) showed the best properties. It had a single-phase hexagonal structure, a nanoscale crystallite size of about 32 nm, a d-spacing of 0.27 nm along the (112) plane, and a grain size that ranged from 300 to 1200 nm while still keeping the proper composition. Electrical tests showed that CZ6 had the highest dielectric constant of 14.06 at 1 MHz. It maintained a low and stable loss tangent (~0.01), lower grain boundary resistance, and improved AC conductivity (from 10⁻⁷ to 10⁻⁶ S/cm), indicating better charge transport. These electrical enhancements correlate strongly with improved biological responses. CZ6 displayed strong apatite formation in simulated body fluid, the highest BSA protein adsorption of 25.05 μg/mL, and an optimized zeta potential of −30.54 mV, which facilitates enhanced biomolecular interactions. Cytocompatibility tests with PSVK-1 (skin keratinocytes) and Wi-38 (lung fibroblasts) confirmed that cell viability remained high at all concentrations. While higher levels of dopants led to the formation of secondary phases and diminished biological responses, CZ6 kept a good balance between electroactivity and biofunctionality. These findings make CZ6 a promising electroactive bioceramic for bone tissue engineering, smart implant coatings, and bioelectret scaffolds, where combining electrical responsiveness with cellular compatibility is important.