A unidirectional porous beta-tricalcium phosphate promotes angiogenesis in a vascularized pedicle rat model

Background: Various types of artificial bone have been developed as alternatives to autologous bone grafts. In designing artificial bone, a porous structure is essential for the infiltration of blood and cells, which promotes angiogenesis within the bone matrix and ultimately ossification. However, it remains unclear what kind of pore system best promotes ossification. Here, we investigated angiogenesis in three different types of porous beta-tricalcium phosphate (beta-TCP) in a vascularized pedicle rat model. Methods: Three types of porous beta-TCP-beta-TCP60 (60% porosity), beta-TCP75 (75% porosity), and unidirectional porous beta-tricalcium phosphate (UDPTCP; 57% porosity) were examined. A cylindrical piece of artificial bone was implanted beneath the superficial inferior epigastric (SIE) vessels in the groin of rats and angiogenesis was allowed to occur. Two weeks after surgery, India ink or lectin was systemically injected to detect newly formed blood vessels originating from the SIE vessels. Immunohistochemistry for von Willebrand factor, alpha-smooth muscle actin, or type IV collagen was performed to clarify the structural features of the newly formed capillaries within the vascularized UDPTCP. Results: The vascularity of the UDPTCP was superior to that of beta-TCP60 and beta-TCP75. The UDPTCP pore structure was completely filled with capillaries at 3 weeks after implantation. Immunohistochemistry showed that the walls of the capillaries contained endothelial cells, pericytes, and basement membrane originating from the SIE vessels, and that the cells proliferated and the basement membrane formed simultaneously as the newly formed capillaries extended through the unidirectional pore structure of the UDPTCP. Conclusions: UDPTCP had greater angiogenic potential than beta-TCP60 and beta-TCP75 in a vascularized pedicle rat model. Vascularized UDPTCP grafts may be an alternative to vascularized autologous bone grafts. (C) 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.