Biowaste to Bioactive Hydroxyapatite–Organic Hybrid Coatings with ECM-Like Topography and Mechanical Integrity for Multifunctional Titanium Implant Coatings

The development of multifunctional coatings for orthopedic and dental implants remains critical to achieving long-term corrosion resistance, osteoconductivity, and antibacterial performance. Hydroxyapatite (HAP), although bioactive, often exhibits brittleness and limited functional integration when used as a standalone coating. Herein, HAP derived from the caprine femur bone was sequentially modified with 5-amino 4-imidazolecarboxamide hydrochloride (AICA), sodium alginate (SA), and polyacrylonitrile (PAN) to form composite coatings (HAP, m-HAP-1, m-HAP-2, and m-HAP-3), which were deposited onto plasma-treated titanium substrates via electrophoretic deposition. The optimized m-HAP-3 coating exhibited reduced crystallite size with partial amorphization, an ECM-like surface morphology, balanced wettability, and improved mechanical integrity. Thermal analysis confirmed the mineral stability with controlled organic degradation. Electrochemical studies revealed an enhanced corrosion resistance and favorable charge transfer behavior. Additionally, m-HAP-3 demonstrated dose-dependent antibacterial activity against Pseudomonas aeruginosa. These results indicate that m-HAP-3 is a stable, bioactive, and antibacterial coating suitable for orthopedic and dental implant applications.