Investigation of structure, morphology, and corrosion behavior of carboxylic acids/hydroxyapatite/chitosan coatings on Ti discs for implants

•Hydroxyapatite/chitosan (HA/Cs) nanocomposites electrodeposited on Ti metal.•Acrylic or acetic acids as cs solvents led to morphology changes of HA/Cs coating.•HA/Cs coated samples exhibited enhanced corrosion resistance compared to uncoated Ti.•The highest corrosion resistance was achieved in presence of acrylic acid (6 %). Titanium (Ti) and its alloys are widely used in bone defect repair owing to their advantages, including high strength, corrosion resistance, and biocompatibility. The formation of a stable oxide layer on Ti implants enhances the osseointegration process. Nevertheless, additional progress is required to improve the incorporation of these implants at the microscopic and nanoscopic levels to achieve a biocompatible interface. The main objective of this study was to enhance the morphology of hydroxyapatite and the corrosion resistance of Ti implants by applying hydroxyapatite/chitosan (HA/Cs) nanocomposite coatings embedded with carboxylic acids. The coatings were fabricated by electrodeposition, wherein various acid concentrations (acrylic and acetic acids) were employed as Cs electrolyte solvents to enhance the adhesion and bond strength with the titanium metal substrate. The microstructures of the HA/Cs coatings were analyzed using X-ray diffraction. The results demonstrated that the structure of HA was affected by the type of acid used and its concentration as the crystallinity increased with a high concentration of acrylic acid. Additionally, the morphology of HA/Cs was analyzed using a transmission electron microscope. The results showed that the morphology of HA/Cs changed from a hexagonal rod-like shape with acrylic acid samples into a needle-like shape in acetic acid samples. The corrosion behavior was investigated using electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) at 37±2ºC. The EIS results showed a high corrosion resistance with phase angles close to −80° and high impedance values of 80.5 kΩ cm2 with a high concentration of acrylic acid. These results indicated the formation of a highly adhesive and stable film on the implants in the test solution. In conclusion, based on this study and our previous work, the corrosion resistance, good biocompatibility, and biomineralization properties of the prepared HA/Cs-coated Ti recommend it as an alternative implant for clinical applications.