Adjacent immobilization of autologous BMP-2 and VEGF envisioning a vascularized bone tissue engineering approach

Reconstruction of large bone defects still remaining a major clinical orthopedic challenge, since repairing of a bone defect is not only the process of new bone formation, but also greatly depends on the formation of new blood vessels - angiogenesis - to supply nutrients and excrete metabolites ^[1]. Consequently, engineered matrices that can induce a concerted differentiation of stem cells into both osteogenic and angiogenic lineages are very promising for the treatment of skeletal injures. Bone morphogenetic proteins (BMPs) and vascular endothelial growth factor (VEGF) govern cell proliferation and bone vascularization to make viable osseous tissue ^[2]. Among BMPs, BMP-2 is a potent osteogenic factor which had been play a key role in the creation of many tissue engineered bone grafts ^[3]. Similarly, the widely used VEGF is not only involved in angiogenesis, but it is also important in the maturation of osteoblasts, ossification, and bone turnover ^[2]. Therefore, the synergistic effect of autologous BMP-2 and VEGF adjacently immobilized over a nanofibrous substrate is hypothesized to lead the osteogenic and angiogenic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) and eventually endothelial cells. To achieve such ambitious goal, an engineered platform was developed to allow the parallel immobilization of BMP-2 and VEGF antibodies. The maximum immobilization capacity of the nanofibrous substrate for each antibody was 4 mg/mL. BMP-2 and VEGF antibodies were also successful immobilized over the same structure in side-by-side fashion, trying to recreate the vasculature of a bone tissue. Furthermore, immobilized antibodies were capable of selectively immobilize the respective growth factor from a biological fluid (i.e. platelet lysate). Using this engineered biofunctionalized platform would be possible to study the synergetic effect of osteogenesis and angiogenesis, targeting a vascularized bone tissue engineering approach.

^[1]S. Almubarak, et al., Bone, 2016;

^[2]D. Barati, et al., J Control Release 223, 2016;

^[3]M. Bouyer, et al., Biomaterials, 2016.

Acknowledgements

The authors would like to acknowledge the Portuguese Foundation for Science and Technology (FCT) for the PhD grant of M.R.C. (PD/BD/113797/2015) financed by the FCT Doctoral Program on Advanced Therapies for Health (PATH) (FSE/POCH/PD/169/2013), the post-doctoral grant of E.M.F (SFRH/BPD/96197/2013), the IF grant of A.M. (IF/00376/2014), and the projects SPARTAN (PTDC/CTM-BIO/4388/2014) and FRONthera (NORTE-01-0145-FEDER-0000232).