The intimate connection, both physical and biochemical, between blood vessels and bone cells has long been recognized. The successfully bone formation is greatly depend on the formation of new blood vessels - angiogenesis - to ensure the 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) that are involved on cell proliferation and bone vascularization to make viable osseous tissue ^[2][3]. 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 parallel immobilized over a nanofibrous substrate (NFMs) is hypothesized to lead the successful angiogenic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs). To achieve such ambitious goal, an engineered platform was developed comprising BMP-2 and VEGF antibodies parallel immobilized at the surface of NFMs, capable to specifically select only the growth factors of interest from a platelet lysate. 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). The angiogenic potential of this engineered biofunctionalized platform was further assessed by culturing hBM-MSCs during 21 days without further induction. Bare NFMs cultured with hBM-MSCs under standard angiogenic differentiation and basal medium were used as positive and negative control, respectively. These biological results indicate that this engineered biofunctionalized platform are able to promote 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).