Development and Characterization of Biogenic Hydroxyapatite Coatings Derived from Crab Shell Waste on Ti6Al4V Substrates

Abstract

In this work, we developed and characterized a hydroxyapatite (HA) ceramic coating derived from Ucides cordatus crab-shell waste and applied it onto Ti–Al–V titanium substrates for biomedical use. Substrate analysis confirmed an α + β two-phase microstructure and Rockwell C hardness of ~35 HRC; optical emission spectrometry indicated a non-conforming Ti–6Al–4V composition (Al slightly above and V slightly below ASTM F136-18 limits), with expected α-phase predominance. Aqueous synthesis of biogenic HA used CaO (from 800 °C calcined shells) reacted with β-tricalcium phosphate (β-Ca3(PO4)2), followed by deposition onto Ti–Al–V surfaces prepared with or without a thermochemical treatment that homogenized roughness (Ra ≈ 0.587 µm). The coatings were continuous, ~95–98 µm thick, and showed good qualitative adhesion. Scanning Electron Microscopy (SEM) revealed porous, nanocrystalline, acicular morphologies typical of biogenic apatite’s. Energy-Dispersive X-ray Spectroscopy (EDS) yielded Ca/P ≈ 1.85–1.88, while X-ray Fluorescence (XRF) indicated Ca-enrichment relative to stoichiometric HA. X-ray Diffraction (XRD) confirmed a predominantly hexagonal HA phase with high crystallinity. These results demonstrate a technically and environmentally feasible route to bioactive coatings using marine biowaste, aligning low-cost, local waste valorization with functional performance on titanium implants.