Novel magnetic nanocomposite injectables: Calcium phosphate cements impregnated with ultrafine magnetic nanoparticles for bone regeneration

Self-setting calcium phosphate cements (CPCs) are some of the few injectables of bioceramic materials applicable to bone repair. Incorporation of nanoparticulates to CPCs is considered a promising process that can improve the mechanical and biological properties of CPCs. Here, we added magnetic nanoparticles (MNPs) at small contents, and examined their effects on the physico-chemical, mechanical, and in vitro biological properties of the CPC composition. The MNPs were coated with a silica layer and had an average size of ∼80 nm. The addition of MNPs did not alter the setting reaction, but dramatically changed the crystal shape and size of the transformed hydroxyapatite, from large plate-like crystals to small needle-like crystals. Mechanical strength was significantly improved from 22 MPa to 33 MPa with the addition of only 0.1% MNPs. A striking difference in cell adhesion of rat bone marrow stromal cells was noticed with the MNPs-incorporation. The cells adhered and spread more actively to the MNP-added CPCs than to the pure CPCs with an approximately 2.5-fold and 4.5-fold increase in cell adhesion and in cell spreading area, respectively. The cell proliferative potential lasted for a longer period of up to 14 days where osteogenic differentiation, determined by alkaline phosphatase activity, was also substantially stimulated by the MNP-incorporation. The results indicate that only a small incorporation of ultrafine MNPs changed the properties of CPCs dramatically, making them more suitable for use in cell culture and repair of bone tissues.