Tissue Engineering of a Vascularized Bone Graft of Critical Size with an Osteogenic and Angiogenic Factor-Based In Vivo Bioreactor

Abstract

Engineering a large vascularized bone graft is a much greater challenge than engineering small bone tissues. Although this is essentially feasible through an osteogenic factor-based in vivo bioreactor technique, the ossification needs improving. This study was aimed to investigate the possibility and efficacy of ectopic cultivation of sizeable bone grafts with large angiogenic and osteogenic factor-loaded natural bovine bone mineral (NBBM) scaffolds. For this purpose, six groups of sizeable composite scaffolds were constructed, consisting of a titanium mesh cage of NBBM or a mixture of NBBM/autogenous bone particles (AB), which were preloaded with 660 μg recombinant human bone morphogenetic protein-7 (rhBMP-7) and/or 4 μg recombinant human vascular endothelial growth factor165 (rhVEGF165). The scaffolds were implanted in bilateral latissimus dorsi muscles in eight pigs to construct in vivo bioreactors. Sequential fluorescence labeling was then applied to trace bone formation at the early stage. The implants were retrieved 12 weeks later. The undecalcified sections were observed in turn under the fluorescence microscope and light microscope to investigate early stage osteogenesis and histology. Moreover, new bone density (BD) was measured with histomorphometry. Compared with rhBMP-7-delivered NBBM scaffolds, rhVEGF165/rhBMP-7-delivered NBBM scaffolds were with more intense intra-scaffold osteogenesis at the early stage and the ultimate sizeable bone grafts of microstructurally more lamellae and trabeculae, and quantitatively higher BD (31.93% vs. 22.37%, p<0.01). This study demonstrated that as for the endocultivation of a large bone graft with bioactive factor-based in vivo bioreactor technique, dual delivery of rhVEGF165/rhBMP-7 has synergic effects on improving early stage bone formation and subsequently bone quality and quantity of the bone grafts.

Bone Graft Prefabrication Following the In Vivo Bioreactor Principle

“…Therefore, even without the transplantation of exogenous osteoprogenitor/stem cells, regeneration of large volume bone tissue can be achieved in an intramuscular environment (Liu et al, 2014). Another critical advantage of this approach is the presence of bone-forming molecules that spread out from the site of muscle injury and lead to natural upregulation of osteogenic signals, including BMPs, transforming growth factor-beta 1 (TGF-β 1 ), and insulin-like growth factor 1 (IGF-1) (Scott et al, 2012).…”

Engineering Photocrosslinkable Bicomponent Hydrogel Constructs for Creating 3D Vascularized Bone

“…By combining patient‐derived cells with biomaterial scaffolds and/or extracellular matrix (ECM) analogues, large volumes of tissue analogues can be prepared . However, these strategies have not been successful in accommodating proper vasculature to compensate slow invasion/perfusion of the host vasculature into the scaffold . Poor vascularization results in ischemia and subsequently poor cell survival and function within days of implantation .…”

Bioreactors for tissue engineering: An update

“…There are two vectors of choice, xenogenic or autogenic [9]. Liu et al in 2014 implanted growth factors loaded scaffolds onto the latissimus dorsi muscles of pigs and successfully induced insitu MSCs to differentiate into osteoblasts and generated well vascularized bone tissue products [10]. Kokemueller et al in 2010 implanted a β-tricalcium phosphate scaffold loaded with morcellized autologous bone graft from the iliac crest to the latissimus dorsi of a patient suffered from chronic mandibular osteomyelitis requiring resection.…”