Fabrication and growth mechanism of multilayered hydroxyapatite/organic composite coatings on the WE43 magnesium alloy

The design and fabrication of anti-corrosive coatings are important to medical implants, especially composite coatings consisting of soft organic and stiff inorganic materials with favorable mechanical properties and corrosion resistance. In this study, a polyethyleneimine/polyacrylic acid (PEI/PAA) multilayered coating is prepared by layer-by-layer (LbL) assembly on the WE43 Mg alloy, followed by mineralization of hydroxyapatite (HA) on the LbL multilayer. The composite coating with a compact surface shows improved corrosion resistance. The corrosion current density i_corr decreases from 14.24 to 2.28 μA/cm² and the hydrogen emission rate diminishes from 0.0185 to 0.0105 mL·cm⁻²·h⁻¹. The formation mechanism, structure, and properties of the organic/inorganic composite coating are investigated systematically. The LbL multilayer is found to play a significant role in initiating nucleation of HA and accommodate the lattice mismatch between the HA coating and WE43 substrate. This study enriches our understanding on the formation of organic/inorganic coatings and this type of composite coating has large potential in biomedical applications such as orthopedics.