Hydroxyapatite is the most suitable biocompatible material for bone implant coatings. However, its brittleness is a major obstacle, and that is why, recently, research focused on creating composites with various biopolymers. In this study, hydroxyapatite coatings were modified with lignin in order to attain corrosion stability and surface porosity that enables osteogenesis. Incorporating silver, well known for its antimicrobial properties, seemed the best strategy for avoiding possible infections. The silver/hydroxyapatite (Ag/HAP) and silver/hydroxyapatite/lignin (Ag/HAP/Lig) coatings were cathaphoretically deposited on titanium from ethanol suspensions, sintered at 900 °C in Ar, and characterized by X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, attenuated total reflection Fourier transform infrared, and X-ray photoelectron spectroscopy. The corrosion stability of electrodeposited coatings was evaluated in vitro in Kokubo's simulated body fluid (SBF) at 37 °C using electrochemical impedance spectroscopy. Bioactivity was estimated by immersion in SBF to evaluate the formation of hydroxyapatite on the coating surface. A microcrystalline structure of newly formed plate-shaped carbonate-hydroxyapatite was detected after only 7 days, indicating enhanced bioactive behavior. Both coatings had good corrosion stability during a prolonged immersion time. Among the two, the Ag/HAP/Lig coating had a homogeneous surface, less roughness, and low values of contact angle.

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In this work, electrophoretic deposition (EPD) was applied to obtain novel hydroxyapatite (HAP)/lignin (Lig) biocomposite coatings on titanium substrate. Nanosized hydroxyapatite powder, prepared by using the modified chemical precipitation method, was used for the fabrication of HAP/Lig composite coatings. EPD was performed at different values of constant voltage and constant deposition time. It was confirmed that control over deposited mass can be achieved by applied voltage and time. The uniform and compact coatings were successfully deposited at applied voltage of 60 V in various deposition times lower than 1 minute. The effect of lignin as natural non-toxic polymer on microstructure, morphology and thermal behavior of biocomposite HAP/Lig coatings was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The electrophoretically deposited HAP/Lig coating has been successfully sintered at lower sintering temperature of 900°C, producing non-fractured coating and indicating that lignin may exhibit adhesive role, strengthening the bonding between HAP particles and substrate surface.