Sr2+-Substituted CaCO3 Nanorods: Impact on the Structure and Bioactivity

Strontium is a natural trace element found in biominerals such as aragonitic coral skeletons and bone apatite. Sr2+substitution in biomaterials has been found to regulate the cellular metabolism, thus enhancing bone healing. Even though Ca2+ substitution for Sr2+ has been described in many phosphate minerals, the impact of such substitution on bioactivity and structure in pure carbonate phases has not been explored. Therefore, here we used a biomimetic approach to synthesize carbonate particles with a controlled size in which Ca2+ was progressively substituted for Sr2+. Through structural investigation by X-ray diffraction, Raman spectroscopy, and electron microscopy techniques including high-resolution transmission electron microscopy and electron diffraction, we studied the precipitation mechanism of Sr-substituted CaCO3 nanorods showing that increasing Sr2+/(Ca2+ + Sr2+) molar fractions lead to stabilization of strontianite, a mineral from the aragonite group, increasing the carbonate crystalline lattice and particle crystallinity. The in vitro bioactivity evaluation attested that the particles bioactivity is maintained even at high Sr2+ concentrations. These outcomes are fundamental for proper evaluation of the role Sr2+ plays in carbonate based biomaterials properties and biomineralization and constitute a starting point to explore (Ca-Sr)­CO3 particles as the next generation of bioactive materials for bone replacement.