Fabrication of intrafibrillar and extrafibrillar mineralized collagen/apatite scaffolds with a hierarchical structure

A biomimetic collagen-apatite (Col-Ap) scaffold resembling the composition and structure of natural bone from the nanoscale to the macroscale has been successfully prepared for bone tissue engineering. We have developed a bottom-up approach to fabricate hierarchically biomimetic Col-Ap scaffolds with both intrafibrillar and extrafibrillar mineralization. To achieve intrafibrillar mineralization, polyacrylic acid (PAA) was used as a sequestrating analog of noncollagenous proteins (NCPs) to form a fluidic amorphous calcium phosphate (ACP) nanoprecursor through attraction of calcium and phosphate ions. Sodium tripolyphosphate was used as a templating analog to regulate orderly deposition of apatite within collagen fibrils. Both X-ray diffraction and Fourier transform infrared spectroscopy suggest that the mineral phase was apatite. Field emission scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction confirmed that hierarchical collagen-Ap scaffolds were produced with both intrafibrillar and extrafibrillar mineralization. Biomimetic Col-Ap scaffolds with both intrafibrillar and extrafibrillar mineralization (IE-Col-Ap) were compared with Col-Ap scaffolds with extrafibrillar mineralization only (E-Col-Ap) as well as pure collagen scaffolds in vitro for cellular proliferation using MC3T3-E1 cells. Pure collagen scaffolds had the highest rate of proliferation, while there was no statistically significant difference between IE-Col-Ap and E-Col-Ap scaffolds. Thus, the bottom-up biomimetic fabrication approach has rendered a group of promising Col-Ap scaffolds, which bear high resemblance to natural bone in terms of composition and structure.