The functionalization of titanium with EDTA to induce biomimetic mineralization of hydroxyapatite

Abstract

A new process is developed to functionalize an inorganic substrate with an organic polycarboxylic chelating agent to obtain a biomimetic template for mimicking biomineralization for the synthesis of films or coatings. A titanium plate is first placed in ethylenediaminetetracetic acid (EDTA) solution to effect chemisorption and self-assembly of EDTA molecules on the plate. The plate is then aged in supersaturated hydroxyapatite [(Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , HA] solution to mimic biomineralization. The functionalization process is found to be very effective in creating a surface with an organized arrangement of carboxylate ions (–COO ^– ) with the orientation of lone pairs of electrons on O perpendicular to or radiating from the substrate surface. The coating is formed through the plate-like outgrowth of HA grains along the [001] direction under the mediation of the functionalized surface, giving rise to the coexistence of two kinds of microstructural patterns in coating. One is a parallel arrangement of the plate-like HA grains with (001) planes preferably parallel to the substrate surface, the other is a radial arrangement of the plate-like HA grains with the [001] direction radiating from one surface core and the (111) planes preferably parallel to the surface. The mineralization mechanism is discussed on the basis of the conformation of the self-assembled EDTA molecules and the interfacial molecular recognition, analogous to the biomineralization, including electrostatic interactions, hydrogen bonding, stereochemical arrangement and geometrical correspondence.