Synthesis, characterization and laser processing of copper-doped nano-hydroxyapatite

Copper-doped nano-hydroxyapatite (Cu-doped HAp) were synthesized via a coprecipitation method at room temperature with pH adjustment, in the context of elaborating scaffolds for bone tissue engineering by Selective Laser Processing. Structural characterization using X-ray diffraction (XRD) and Rietveld refinements confirmed the substitution of copper ions into the Ca (2) site within the hexagonal P6₃/m apatite structure, while Fourier-difference mappings provided atomic-scale evidence of this substitution. The Cu for Ca (2) substitution was also supported from FTIR spectra analysis. Transmission Electron Microscopy (TEM) revealed that copper doping reduced HAp nanocrystallite growth, though it preserved the characteristic anisotropic growth along the crystallographic direction. The incorporation of divalent copper (Cu²⁺) introduced a broad absorption band between 500–1500 nm, attributed to its 3d 9 electronic configuration. This optical property is critical for Laser Processing, as it enhances energy absorption at common laser wavelengths, improving sintering efficiency and scaffold integrity. Preliminary experiments successfully fabricated consolidated copper-doped nano-hydroxyapatite (Cu-HAp) rods via Selective Laser Processing. The results demonstrated that copper concentration critically determines structural outcomes, with optimal doping enabling direct consolidation into mechanically rigid objects capable of manual handling. During sintering, hydroxyapatite (HAp) remained the primary phase, while partial decomposition led to the formation of α-tricalcium phosphate (α-TCP) as a secondary phase, confirming the process achieved phase stability under extreme thermal conditions. A notable color transition from pale blue to pink was observed during processing, that could be due to either thermal reduction of Cu²⁺ to Cu⁺ under laser-induced high-energy conditions or oxidation reactions converting Cu 2 ⁺ to Cu³ ⁺ through interactions with atmospheric oxygen. The chromatic shift coupled with α-TCP formation, leading to easy-to-handle ceramic rods, provide direct evidence that localized temperatures within laser-irradiated zones exceeded 1200°C, i.e. the threshold required for effective HAp sintering. • Incorporation of copper in nano-hydroxyapatite, by a coprecipitation process. • Coupled XRD refinement refinements, chemical analyses, TEM observations and optical spectroscopy to identify clearly that Cu 2+ positioning on Ca (2) site. • Cu 2+ as the key parameter to prepare consolidated rods from Selective Laser Processing.