<i>In Situ</i> Production of Pre-Vascularized Synthetic Bone Grafts for Regenerating Critical-Sized Defects in Rabbits

Abstract

Reconstructing large bone defects caused by severe trauma or resection of tumors remains a challenge for orthopedic and plastic surgeons. Free flaps comprised of a muscle flap with fibula bone and its vascularized bed can be transplanted to the reconstruction site to achieve healing. However, this transplantation technique adds morbidity, and requires extensive microsurgery and sculpting of the bone tissue to adapt the graft to both the vasculature and the anatomy of the bone defect. The aim of the current study is to evaluate an alternative approach consisting of the in situ production of a pre-vascularized synthetic bone graft and its subsequent transplantation to a critical-sized bone defect. 3D printed chambers containing biphasic calcium phosphate (BCP) granules, perfused by a local vascular pedicle, with or without the addition of stromal vascular fraction (SVF), were subcutaneously implanted into New Zealand White female rabbits. The SVF was prepared extemporaneously from autologous adipose tissue, while the vascular pedicle was isolated from the inguinal site. Chambers filled with BCP alone served as controls. After 8 weeks, the constructs containing a vascular pedicle exhibited abundant neovascularization, with significant numbers of blood vessels sprouting from the pedicle, which was further enhanced by the addition of SVF. These pre-vascularized synthetic bone grafts were then transplanted into 15 mm critical-sized segmental ulnar defects for a further 8 weeks. Micro-CT and decalcified histology revealed that pre-vascularization of synthetic bone grafts led to significantly enhanced bone regeneration. This pre-clinical study demonstrates the feasibility and efficacy of in situ production of pre-vascularized synthetic bone grafts for regenerating large bone defects, and will address an important clinical need.