Dual growth factor delivery from biofunctionalized allografts: Sequential VEGF and BMP-2 release to stimulate allograft remodeling

Abstract

Autografts have been shown to stimulate osteogenesis, osteoclastogenesis, and angiogenesis, and subsequent rapid graft incorporation. Large structural allografts, however, suffer from limited new bone formation and remodeling, both of which are directly associated with clinical failure due to non-unions, late graft fractures, and infections, making it a priority to improve large structural allograft healing. We have previously shown the osteogenic ability of a polymer-coated allograft that delivers bone morphogenetic protein-2 both in vitro and in vivo through both burst release and sustained release kinetics. In this study, we have demonstrated largely sequential delivery of bone morphogenetic protein-2 and vascular endothelial growth factor from the same coated allograft. Release data showed that loading both growth factors onto a polymeric coating with two different techniques resulted in short-term (95% release within 2 weeks) and long-term (95% release within 5 weeks) delivery kinetics. We have also demonstrated how released VEGF, traditionally associated with angiogenesis, can also provide a stimulus for allograft remodeling via resorption. Bone marrow derived mononuclear cells were co-cultured with VEGF released from the coated allograft and showed a statistically significant (p < 0.05) and dose dependent increase in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclasts. Functionality of these osteoclasts was assessed quantitatively and qualitatively by evaluating resorption pit area from both osteo-assay plates and harvested bone. Data indicated a statistically significant higher resorption area from the cells exposed to VEGF released from the allografts over controls (p < 0.05). These results indicate that by using different loading protocols temporal control can be achieved when delivering multiple growth factors from a polymer-coated allograft. Further, released VEGF can also stimulate osteoclastogenesis that may enhance allograft incorporation, and thus mitigate long-term clinical complications. © 2017 Orthopedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1086-1095, 2017.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

“…Considering this concept, several studies have focused their efforts in the design of sequential or dual delivery systems for both vascular endothelial growth factor (VEGF) and the bone morphogenetic protein-2 (BMP-2) [151, 152]. The combination of both growth factors enhances the chances of bone regeneration compared to scaffold loaded with a single growth factor.…”

Large scale segmental bone defect healing through the combined delivery of VEGF and BMP‐2 from biofunctionalized cortical allografts

“…In our previous work we developed a polymeric system that can deliver VEGF and BMP‐2 simultaneously from structural cortical allografts, with the VEGF eluting earlier than the BMP‐2 . We have confirmed the bioactivity of released BMP‐2 both in vitro and in vivo and have demonstrated that released VEGF can stimulate enhanced osteoclastogenesis when combined with RANK ligand, in vitro .…”

“…In our previous work we developed a polymeric system that can deliver VEGF and BMP‐2 simultaneously from structural cortical allografts, with the VEGF eluting earlier than the BMP‐2 . We have confirmed the bioactivity of released BMP‐2 both in vitro and in vivo and have demonstrated that released VEGF can stimulate enhanced osteoclastogenesis when combined with RANK ligand, in vitro . In vivo evaluation of BMP‐2 delivery from coated allografts showed organized bone formation along the length of the defect, fully encapsulating the coated allograft but the BMP‐2 concentration delivered in those studies was high.…”

“…This polymer is then loaded with one or more growth factors with the design goal that the factors elute with a temporal precision shown to benefit bone repair by stimulating vascularization, osteoclastic resorption of the allograft, and osteoblastic formation of new bone. Results from our previously published papers have revealed that (1) adsorbing VEGF to the polymer coating surface and encapsulating BMP‐2 within the coating result in the initial burst release of VEGF and the subsequent more sustained release of BMP‐2, (2) the released BMP‐2 is bioactive and unharmed by the encapsulation process and the released VEGF induces the differentiation of monocytes to osteoclasts in vitro when paired with RANK‐L (which is endogenously available), and (3) the differentiated osteoclasts are functional and capable of resorbing mineralized bone …”

“…Allografts were harvested, polymer‐coated, and loaded with growth factors as previously described . Briefly, femoral bone samples were harvested from male Sprague–Dawley rats (150–250 g), cleaned of soft tissue, bone marrow aspirated, and agitated in a chloroform solution overnight to reduce the residual fatty tissue.…”