Elaboration and synthesis of the whitlockite phase using limestone dust: <i>in vitro</i> bioactivity for biomedical applications

Abstract

Calcium silicate-based bioceramics have attracted attention in biomedical applications due to their calcium and silicon contents, which are essential for bone health. Whitlockite (WH), the second most abundant inorganic component of bones after hydroxyapatite (HAP), constitutes 20-35% of bones by weight and exhibits excellent biological properties, making it particularly attractive for tissue engineering. It is therefore essential to synthesize the WH phase using cost-effective and eco-friendly by-products. This study aims to synthesize the whitlockite phase using dicalcium silicate (larnite, Ca₂SiO₄). Dicalcium silicate was synthesized from a mixture of limestone dust (LD), a by-product consisting essentially of calcium carbonate (CaCO₃), and soda lime glass powders, as a source of silicon dioxide (SiO₂). Additionally, the surface reactivity and bioactivity of the composite sample were evaluated <i>in vitro</i> by immersing it in artificial saliva (SA) and in a simulated body fluid (SBF) for time periods ranging from 1 hour to 5 hours. The mineralogical and microstructural properties of the samples were characterized using XRD, FTIR and SEM analysis techniques. The characterization of the obtained powders indicated that the whitlockite phase synthesized through a co-precipitation method exhibited good bioactivity both in artificial saliva (SA) and simulated body fluid (SBF). Moreover, the analysis revealed the development of a hydration phase of rosenhahnite (Ca₃Si₃O₁₀H₂) and the formation of a hydroxyapatite (Ca₅(PO₄)₃(OH)) phase within 1 hour of immersion in both bioactive media. The morphology of the samples was analyzed using SEM, which showed significant grain growth and consolidation after 1 hour of immersion in artificial saliva and simulated body fluid. After 5 hours, the grains appeared to be well connected with each other, indicating good consolidation.