Multifunctional Sr, Mg, Ag-substituted octacalcium phosphate/carboxymethyl chitosan scaffolds: Antibacterial activity and osteogenic differentiation of human mesenchymal stem cells

Abstract

Numerous studies indicate that octacalcium phosphate (OCP) possesses promising bone regenerative properties. To further improve the regenerative properties of OCP, several ionic substitutions have been proposed. However, knowledge regarding the synergic effect of multiple ions substituted in OCP crystals and fabricated scaffolds is lacking. In this work, plate-like OCP crystals substituted with 1 and 2.5 mol.% of Mg2+, Sr2+ and Ag+ were prepared by the wet precipitation method. Rietveld refinement analysis indicated a successful substitution of Ca2+ by Mg2+, Sr2+and Ag+ ions. The prepared substituted OCP powders showed a high antibacterial effect towards Gram-negative and Gram-positive bacteria. Further, composite scaffolds based on substituted OCP and carboxymethyl chitosan were prepared by the freeze-crosslinking method. The scaffolds had a highly porous structure, with interconnected pores and homogeneously dispersed OCP within the polymer matrix, and high stability in simulated physiological conditions during 28 days. Good viability and proliferation of human bone marrow-derived mesenchymal stem/stromal cells were confirmed by Live/Dead and CyQUANT assays. Additionally, successful osteogenic differentiation was confirmed by quantification of alkaline phosphatase activity and immunocytochemical staining for type I collagen. Results indicate that ionic substitutions with 1.0 mol.% have the most beneficial effect on stem cell differentiation towards osteoblast phenotype.