Effect of nanostructure of mineralized collagen scaffolds on their physical properties and osteogenic potential.

Tissue engineering has enabled development of nanostructured collagen scaffolds to meet current challenges in regeneration of lost bone. In this study, extrafibrillarly-mineralized and intrafibrillarly-mineralized collagen scaffolds were fabricated separately by a conventional crystallization method and a biomimetic, bottom-up crystallization method. Atomic force microscopy (AFM) was employed to examine the nanotopography and nanomechanics of the mineralized collagen scaffolds. The in vitro cell responses to the surface of the mineralized collagen scaffolds were analyzed by laser scanning microscope and field emission scanning electron microscopy. AFM imaging showed that these two mineralized collagen scaffolds exhibited different nanostructure, including the size, morphology and location of the apatites in collagen fibrils. The nanomechanical testing demonstrated that the intrafibrillarly-mineralized collagen scaffold, with bone-like hierarchy, featured a significantly increased Young's modulus compared with the extrafibrillarly-mineralized collagen scaffold in both dry and wet conditions. However, these two mineralized collagen scaffolds had a similar thermal behavior. From the cell culture experiments, the intrafibrillarly-mineralized collagen scaffold showed higher cell proliferation and alkaline phosphatase activity than the extrafibrillarly-mineralized collagen scaffold. The utmost significance of this study is that the nanostructure of the mineralized collagen scaffolds can affect the initial cell adhesion, morphology and further osteogenic potential. The present study will help us to fabricate novel biomaterials for bone grafting and tissue engineering applications.