Oriented bone formation using biomimetic fibrin hydrogels with three-dimensional patterned bone matrices

Cortical bone exerts its biological properties through internal orientations of hydroxyapatite. Recently, we succeeded in fabricating three-dimensional (3D) patterns of bone matrices using fibrin gels. We hypothesized that these fibrin gels would induce cortical bone-like tissue in vivo and offer promising prospects for biomimetic materials. The purposes of this study were to assess the characteristics of osteoblastic-induced fibrin gels in vitro and evaluate whether fibrin gels with biomimetic matrices formed cortical bone-like tissue in vivo. When bone marrow stromal cell (BMSC)-containing fibrin gels were uniaxially fixed and cultured, BMSCs became aligned parallel to the fixed direction. The tensile strengths of the gels increased dramatically from 1.5 to 218 kPa after 50 days in culture. Furthermore, Fourier-transform infrared spectroscopy revealed that the fibrin gel constituents changed into those of native bone. Quantitative analyses of specific components demonstrated that the amounts of calcium and osteopontin in the gels increased with prolonged culture. After subcutaneous implantation into immunodeficient mice, cortical bone-like tissues that possessed layered structures were formed. The results indicated that 3D patterned bone matrices induced 3D patterned cortical bone formation in vivo. These biomimetic materials containing 3D patterned bone matrices are promising tools for the field of bone regenerative medicine.