In Vitro Characterization of Carbon-Nanotube-Reinforced Hydroxyapatite Composite Coating on 316L Stainless Steel

This investigation focused on a comparison between hydroxyapatite (HA) and carbon-nanotube-reinforced hydroxyapatite composite (CNTs/HA) coatings. The HA and CNTs/HA composite (with 5 wt% CNTs) coatings were prepared with the sol-gel method on 316L stainless steel. Phase evaluation by means of XRD and Raman spectroscopy was performed on the HA and CNTs/HA composite coatings. The coatings were immersed in simulated body fluid (SBF) in order to evaluate the biological properties of the coatings. During the first week of immersion, the increase in the amount of Ca2+ precipitation in the SBF when CNTs/HA was used was lower than for the HA coatings. This behavior can be related to the difference in the amount of amorphous phases in the two types of coatings. The microstructure of the coatings was studied with AFM and SEM. The results showed that the crystallinity of the composite coating is greater than that of the HA coatings.