Biomimetic synthesis of Mg-substituted hydroxyapatite nanocomposites and three-dimensional printing of composite scaffolds for bone regeneration

In this study, we have successfully fabricated magnesium (Mg) substituted hydroxyapatite nanocomposites (Mg-HA) by utilizing type I collagen (COL I) and citric acid (CA) through a bitemplate-induced biomimetic mineralization approach. The obtained composite nanoparticles were subsequently mixed with chitosan (CHI) and gelatin (Gel) to prepare porous scaffolds with interconnected structures by three-dimensional (3D) printing technique. The Mg-HA powders and composite scaffolds were characterized. The results showed that the substitution of Mg for Ca ions reduced the crystallinity of HA crystals, but did not significantly affect the size and structure of the nanocomposites. The morphology of Mg-HA scaffolds turned smoother compared with the HA scaffolds with Mg substitution. Furthermore, the biocompatibility of Mg-HA composite scaffolds was evaluated by metal ion release, cell attachment, proliferation, and differentiation of MC3T3-E1 cells. According to the results, as the more Ca2+ was substituted by Mg2+, the more Mg2+ was released from the samples and the pH in cultured medium was more acidic. It was suggested that Mg-HA scaffolds presented higher cell attachment, proliferation rate, increased expression of alkaline phosphatase (ALP) activity and osteogenic related gene, including osteocalcin (OCN), runt-related transcription factor 2 (RUNX2), and COL I. Therefore, it was indicated that the 3D printed Mg-HA composite scaffolds with excellent biocompatibility and bioactivity were a potential candidate in bone tissue engineering.