Figure 3. 19F MAS-NMR spectra of grown apatite at different temperatures 37ᵒC, 70ᵒC and 90ᵒC. Asterisks marks are the spinning side bands, and the red dot corresponds to weak peak at -95 ppm
Surface Topography Characterization
When a dental implant osseointegrates to living bone, it is essential that a bioactive layer is formed on its surface.44 In our case, apatite is used as the bonding interface, while investigating the effect of topographical changes and chemistry of the substrates at different temperatures to allow the comparison between different surface properties on the morphology, organization, and dimensions of the synthesized apatite coatings. The orientation of the crystals can be controlled by the stereochemical recognition at the interface, determining the crystallographic orientation of the synthesized crystals. On the other hand, epitaxial growth produces an anisotropic strain at the interface that results in determining the shape of crystals rather than the orientation.45 Further understanding of these concepts, crystal growth can be fine-tuned to produce advanced hierarchical biomaterials.
The surface features of all substrates employed in this study, were inspected using SEM. We showed that non-etched titanium (NE-Ti) has grooves running in different directions, this is secondary to the cutting of the samples (Figure S2a), However, etching the titanium (E-Ti) surface resulted in revealing the grain boundaries and increasing the submicron surface groove size and roughness (Figure S1b). On the other hand, irregular asymmetrical grooves were observed on the unpolished sapphire (U-Sa) surface (Figure S1c), whereas polished sapphire (P-Sa) substrate exhibited smooth surface topography (Figure S1d). After incubation of the samples in the fluoride-rich supersaturated calcium phosphate solution at different temperatures, we have observed multiple shapes and morphologies made from apatite nanocrystals (Chart 1), grown across the surfaces of our substrates, including the titanium and sapphire.
Effect of Substrate and Temperature on the Apatite Crystal Morphology and Organization .
The wet chemical method used during this study is advantageous compared to the other wet chemical methods that form apatite crystals, as this method relies on the calcium and phosphate components from one source (HAp powder). This results in controlling the molar ratio of Ca:P to be 1.67, therefore it provides the accurate stoichiometry for apatite formation. However, as other mineralization solutions supply the calcium and phosphate from different sources, which can
Chart 1. Chart showing the apatite coatings morphologies observed on the different substrates at different temperatures.