The Influence of Phosphate Ion Concentrations on the Properties of Wollastonite-Apatite-Based Cements

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© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.Current approaches for developing bone substitutes prioritize materials with adequate mechanical properties, tailored structures, and resorbing ability under physiological conditions. In this way, new self-setting wollastonite-based apatite cements were prepared by mixing wollastonite powders with a liquid phase containing phosphoric acid and ammonium phosphate in different concentrations. The mixture formed a workable paste that can be molded in different shapes. The cement was analyzed through X-ray diffraction, Fourier Transform Infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The analysis showed that the main product of the hydration process is a mixture of crystalline wollastonite and hydroxyapatite. In addition, Raman spectroscopy confirmed the presence of an amorphous phase composed of silica and amorphous calcium phosphate for all samples. The setting times of the cement pastes were measured using a Gilmore needle indentation technique, and the compressive strength was determined using a Universal Testing Machine. The initial setting time was reduced from 142 ± 5 to 10 ± 1 min by increasing 30% of the concentration of phosphate ions in the solution. Furthermore, the higher content of phosphate ions enhanced the compressive strength by 310% compared with cements containing lower concentrations, reaching a resistance of 14 ± 2 MPa. The in vitro biocompatibility was confirmed by MTT assay, wherein no cytotoxicity of the cements was observed against murine embryonic fibroblast cells. Our results provided valuable information for designing wollastonite-based cements with optimal handling, mechanical, and biological properties using a liquid medium with adequate conditions to match the desired final product.

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