Hydroxyapatite-Based Coatings for Corrosion Resistance and Self-healing in Biomedical and Industrial Applications.

Understanding and controlling the relationship between biomaterial structure and biological function is essential for the long-term success of biomedical implants. Hydroxyapatite (HAp), a biocompatible calcium phosphate-like bone mineral, has garnered attention as a multifunctional coating material due to its corrosion resistance and bioactivity. This review critically examines recent advances in HAp-based coatings, with a focus on fabrication techniques, microstructural design, and corrosion protection mechanisms. Emphasis is placed on functional enhancements through surface engineering, ion substitution (e.g., F⁻, Zn²⁺, Sr²⁺), coordination chemistry, and incorporation with nanocomposites, such as carbon allotropes, biopolymers, and metal oxides. The dual role of HAp in promoting osteointegration and preventing localized corrosion is explored across diverse metallic substrates (Mg, Ti, NiTi, and stainless steel), with comparative insights from saline and simulated body fluids (SBFs) environments. The review also highlights emerging smart coatings with diagnostic and self-healing capabilities, offering guidance for the development of next-generation HAp-based coatings for durable and multifunctional biomedical implants. STATEMENT OF SIGNIFICANCE: Hydroxyapatite (HAp), a calcium phosphate mineral, has been established as a useful material due to its remarkable bioactivity and biocompatibility. Numerous existing studies explore the use of HAp in bone regeneration and integration; however, its potential in multifunctional coatings leftovers underexplored. The present review explores the growing interest and significance of the HAp-based coatings in ensuring the corrosion resistance of metallic implants. HAp provides an environmentally friendly and non-toxic alternative to the traditional coatings or inhibiting systems that suffer from limited durability, poor adhesion, and toxicity. HAp-based coatings are associated with self-healing, biocompatibility, and osteointegration capabilities along with anticorrosion potentials. This review explores advancements in synthesis, ion substitution, nanocomposites, and smart self-healing systems, providing insights for next-generation implant coatings, enhancing longevity, patient safety, and corrosion protection.