Fabrication of initial trabecular bone-inspired three-dimensional structure with cell membrane nano fragments.

The extracellular matrix of trabecular bone has a large surface exposed to the bone marrow and plays important roles such as hematopoietic stem cell niche formation and maintenance. In vitro reproduction of trabecular bone microenvironment would be valuable not only for developing a functional scaffold for bone marrow tissue engineering but also for understanding its biological functions. Herein, we analyzed and reproduced the initial stages of trabecular bone formation in mouse femur epiphysis. We identified that the trabecular bone formation progressed through the following steps: (i) partial rupture of hypertrophic chondrocytes; (ii) calcospherite formation on cell membrane nano fragments (CNFs) derived from the ruptured cells; and (iii) calcospherite growth and fusion to form the initial three-dimensional (3D) structure of trabecular bones. For reproducing the initial trabecular bone formation in vitro , we collected CNFs from cultured cells and used as nucleation sites for biomimetic calcospherite formation. Strikingly, almost the same 3D structure of the initial trabecular bone could be obtained in vitro by using additional CNFs as a binder to fuse biomimetic calcospherites.