Anchoring structure of the calvarial periosteum revealed by focused ion beam/scanning electron microscope tomography

An important consideration in regeneration therapy is the fact that the tissue surrounding an organ supports its function. Understanding the structure of the periosteum can contribute to more effective bone regeneration therapy. As a cellular source, the periosteum also assists bone growth and fracture healing; this further necessitates its direct contact with the bone. However, its anchoring strength appears to be inexplicably stronger than expected. In this study, we used focused ion beam/scanning electron microscope tomography to investigate ultrathin serial sections as well as the three dimensional ultrastructure of the periosteum to clarify the architecture of its anchoring strength, as such assessments are challenging using conventional methods. We discovered perforating fibres that arise from the bone surface at 30 degree angles. Additionally, the fibres across the osteoblast layer were frequently interconnected to form a net-like structure. Fibroblast processes were observed extending into the perforating fibres; their morphologies were distinct from those of typical fibroblasts. Thus, our study revealed novel ultrastructures of the periosteum that support anchorage and serve as a cellular source as well as a mechanical stress transmitter.