The structural, thermal, spectroscopic, morphologic and in vitro biocompatibility properties of boron-doped hydroxyapatites co-doped with dysprosium: An experimental and theoretical investigation

Abstract

Hydroxyapatite (HA) stands as a pivotal biomaterial in orthopedic applications due to its chemical similarity to natural bone mineral. This study presents a comprehensive experimental and theoretical investigation into the structural, thermal, spectroscopic, morphological, and biocompatibility properties of Boron (B)-doped HA co-doped with varying concentrations of Dysprosium (Dy). Samples were synthesized via a wet chemical method and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopy, thermal analysis (TGA/DTA), and scanning electron microscopy (SEM). Complementing the experimental work, Density Functional Theory (DFT) calculations were employed to analyze the electronic structure, density, and radiation shielding parameters. XRD analysis confirmed the formation of the hexagonal HA phase alongside a minor beta-tricalcium phosphate (beta-TCP) secondary phase (0.8-2.3%). The introduction of dopants induced lattice distortions and a systematic reduction in crystallite size, ranging from 34.65 nm for pure HA to 29.30 nm for the highest Dy-containing sample (1.6Dy-0.8B-HA), with crystallinity indices decreasing from 1.17 to 0.70 upon B doping and varying between 0.66 and 0.92 for the co-doped compositions. Theoretically, while B doping slightly widened the band gap from 4.35 eV to 4.56 eV, the incorporation of Dy systematically narrowed it from 4.43 eV (0.4Dy-0.8B-HA) to 4.12 eV (1.6Dy-0.8B-HA), attributed to the introduction of localized Dy-4f states within the forbidden gap. The theoretical and experimental density values showed excellent agreement, with densities increasing from approximately 3115-3119 kg m-3 for B-doped HA to 3188-3320 kg m-3 for the highest Dy content, reflecting the progressive substitution of Ca2+ by the significantly heavier Dy3+ cation. Notably, the linear attenuation coefficient (LAC) increased significantly with Dy concentration, from 1.832 cm-1 (pure HA) to 2.139 cm-1 (1.6Dy-0.8B-HA) at 50 keV, with corresponding reductions in half-value layer (HVL) from 0.378 cm to 0.324 cm at the same energy, indicating progressively enhanced radiation shielding capabilities. These findings collectively suggest that B-Dy co-doped HA possesses tunable electronic and structural properties alongside improved radiation shielding potential, making it a promising multifunctional candidate for advanced bone tissue engineering, bioimaging, and biomedical radiation protection applications.