Calcified Honeycomb-shaped Collagen Maintains its Geometry in Vivo and Effectively Induces Vasculature and Osteogenesis

Honeycomb collagen (HC) with its unique geometric structure has been used in cell culture experiments to study the three-dimensional (3D) effects of the artificial matrix. When implanted in animal tissue however, HC was easily distorted and its geometric structure crushed. In order to elucidate the effect of 3D geometry of this scaffold in both in vitro and in vivo, we attempted to give it rigidity by calcifying and coating HC with hydroxyapatite. By using a calcifying solution with a high calcium (15 mM) and phosphate (9 mM) concentration, hydroxyapatite was evenly precipitated on the surface of HC, obtaining 10 times higher weight than the original HC. A mechanical strength test of the calcified HC showed a 4 times higher compression modulus than the original HC. Implantation of calcified HC into rats subcutaneously with BMP effectively induced bone, comparable with the HC and another conventional scaffold. Moreover, implantation of calcified HC without BMP induced vasculature along individual tunnels of the calcified HC, while the implantation of HC alone without BMP led to the degradation of the scaffold at 4-8 weeks.