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Plant extracts have been regarded as “green” alternatives as inhibitors for metal corrosion prevention and mitigation. Therefore, understanding the electrochemical properties and the reaction mechanisms of the electro-active compounds from the plant extracts is necessary to further explore the mechanism and application of the plant extract-based additives for corrosion prevention and mitigation. Among different plant derived chemicals, aromatic compounds are among the most effective for corrosion inhibition and mitigation. Thus, the electrochemical properties of seven aromatic active compounds from the plant extracts – caffeic acid, thymol (2‑isopropyl‑5‑methylphenol, IPMP), gallic acid (3,4,5‑trihydroxybenzoic acid), tannic acid, lawsone (2‑hydroxy‑1,4‑naphthoquinone), wedelolactone, and ellagic acid are studied using multiwalled carbon nanotube modified glassy‑carbon electrode, and reported to enhance the fundamental understanding of their redox behavior at different environmental pH conditions.

The clinical application of magnesium (Mg)-based alloys as temporary orthopedic implants is highly limited by their rapid corrosion rate in the physiological environment. Herein, an anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone was prepared on AZ31 Mg alloy to improve its corrosion resistance. Lawsone was incorporated into the coating as a corrosion inhibitor to enhance the passive corrosion protection of the PCL coating through its strong chelation ability of dissolving Mg2+. Anti-corrosion properties of the coatings were assessed by electrochemical techniques and in vitro immersion tests, and the results demonstrated a remarkable improvement in corrosion resistance of the bare Mg alloy. In addition to the corrosion inhibition effect, incorporation of lawsone provided the coating with a strong antibacterial activity against Escherichia coli and Staphylococcus aureus bacterial strains. Moreover, the fabricated coating was cytocompatible (viability of > 85 %) toward human fetal osteoblast cells. The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants.