Exploring the fabrication, properties, and morphology of fluorine substituted hydroxyapatite coatings

Hydroxyapatite (HAp), resembling human bone tissue, is a promising biomaterial for dental and hip prosthetics. Incorporating fluorine ions enhances HAp properties, particularly in dental restoration. This new study examines the physicochemical and biological properties of fluorine substituted hydroxyapatite (FHAp) coatings. Structural and morphological properties of the coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental composition of the FHAp coatings was studied using energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy. Fourier Transform Infrared spectroscopy (FTIR) investigations were also conducted. The typical peaks identified in XRD patterns of the FHAp were associated with pure hydroxyapatite with hexagonal structure. The general XPS spectrum of FHAp coatings shows peaks corresponding to the constituent elements of stoichiometric HAp as well as the presence of F that was used as a substituent. Consequently, the FTIR studies results underlined the presence of hydroxyapatite in the FHAp coatings. The SEM images reveal the presence of a uniform and continuous layer of particle conglomerates evenly distributed across the FHAp surface. Valuable information about the FHAp coating's wettability, adhesion and coating thickness were also obtained. Also, the AFM images suggest the absence of the significant irregularities from the surface of the FHAp coatings. Investigations of FHAp coatings reveal promising outcomes for cell viability and proliferation. Detailed analysis of FHAp's 3D surface characteristics and roughness, following ISO 25178–2:2012 standards, highlights their favorable biocompatibility, supporting MG63 cell proliferation. The surface roughness parameters of FHAp coatings were found to vary, with Sa values spanning from 0.029 ± 0.004 μm to 0.778 ± 0.007 μm, while Sq ranged from 0.035 ± 0.005 μm to 0.907 ± 0.011 μm. Furthermore, FHAp exhibits skewness (Ssk) from −0.048 ± 0.006 to 0.195 ± 0.009, kurtosis (Sku) from −0.600 ± 0.011 to −1.050 ± 0.021, and fractal dimension from 2.14 ± 0.01 to 2.19 ± 0.01, indicating consistent surface complexity and favorable properties. The Minkowski Functionals mirror the morphological observations from AFM images, emphasizing their dynamic influence on the samples' surfaces.