The Impact of Vascular Supply on Endochondral Bone Regeneration in Centimeter-Sized Porous Chambers

The current clinical treatment of large bone defects in humans primarily relies on autologous bone grafts. However, the use of autologous bone grafts can be limited by tissue availability, variable bone quality, and donor site morbidity. In response to these challenges, endochondral bone regeneration has emerged as a promising approach. This method mimics endochondral ossification by chondrogenically differentiating or stimulating cells of various cell sources into 'callus mimics' (CMs). We previously demonstrated the feasibility of endochondral bone regeneration in restoring bone defects using 'mesenchymal stromal cell' (MSC)-derived devitalized CMs in small and large animals. To scale up the size of treated defects using these CMs, we propose the introduction of a vascular supply. In this study, an arteriovenous (AV) loop was introduced as a vascular supply to devitalized 'MSCs'-derived CMs in a centimeter-scale porous chamber in rats. The extent of vascularization and remodeling was evaluated for chambers filled with CMs in the presence or absence of an AV loop at 4 and 8 weeks. While the AV loop's role in vascularization is established, our study uniquely shows that in a challenging in vivo setting with devitalized callus mimics, the AV loop was critical for initiating bone formation. Mineralization was observed in all groups via microCT, but bone tissue formed only in the AV loop group (50% of samples at 8 weeks), underscoring its influential role in supporting both vascular invasion and bone formation.