Although growth factors naturally exert their morphogenetic influences within the context of the extracellular matrix microenvironment, the interactions among growth factors, their receptors, and other extracellular matrix components are typically ignored in clinical delivery of growth factors. We present an approach for engineering the cellular microenvironment to greatly accentuate the effects of vascular endothelial growth factor-A (VEGF-A) and platelet-derived growth factor-BB (PDGF-BB) for skin repair, and of bone morphogenetic protein-2 (BMP-2) and PDGF-BB for bone repair. A multifunctional recombinant fragment of fibronectin (FN) was engineered to comprise (i) a factor XIIIa substrate fibrin-binding sequence, (ii) the 9th to 10th type III FN repeat (FN III9-10) containing the major integrin-binding domain, and (iii) the 12th to 14th type III FN repeat (FN III12-14), which binds growth factors promiscuously, including VEGF-A165, PDGF-BB, and BMP-2. We show potent synergistic signaling and morphogenesis between α5β1 integrin and the growth factor receptors, but only when FN III9-10 and FN III12-14 are proximally presented in the same polypeptide chain (FN III9-10/12-14). The multifunctional FN III9-10/12-14 greatly enhanced the regenerative effects of the growth factors in vivo in a diabetic mouse model of chronic wounds (primarily through an angiogenic mechanism) and in a rat model of critical-size bone defects (through a mesenchymal stem cell recruitment mechanism) at doses where the growth factors delivered within fibrin only had no significant effects.

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BackgroundAdipose-derived mesenchymal stem cells (MSCs) have been gaining fame mainly due to their vast clinical potential, simple isolation methods and minimal donor site morbidity. Adipose-derived MSCs and microvascular endothelial cells have been shown to bear angiogenic and vasculogenic capabilities. We hypothesized that co-culture of human adipose-derived MSCs with human adipose-derived microvascular endothelial cells (HAMECs) will serve as an effective cell pair to induce angiogenesis and vessel-like network formation in three-dimensional scaffolds in vitro.MethodsHAMECs or human umbilical vein endothelial cells (HUVECs) were co-cultured on scaffolds with either MSCs or human neonatal dermal fibroblasts. Cells were immunofluorescently stained within the scaffolds at different time points post-seeding. Various analyses were performed to determine vessel length, complexity and degree of maturity.ResultsThe HAMEC:MSC combination yielded the most organized and complex vascular elements within scaffolds, and in the shortest period of time, when compared to the other tested cell combinations. These differences were manifested by higher network complexity, more tube alignment and higher α-smooth muscle actin expression. Moreover, these generated microvessels further matured and developed during the 14-day incubation period within the three-dimensional microenvironment.ConclusionsThese data demonstrate optimal vascular network formation upon co-culture of microvascular endothelial cells and adipose-derived MSCs in vitro and constitute a significant step in appreciation of the potential of microvascular endothelial cells and MSCs in different tissue engineering applications that can also be advantageous in in vivo studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-015-0251-6) contains supplementary material, which is available to authorized users.

Sustained and controlled delivery of growth factors, such as bone morphogenetic protein 2 (BMP-2), from polymer scaffolds has excellent potential for enhancing bone regeneration. The present study investigated the use of novel sintered polymer scaffolds prepared using temperature-sensitive PLGA/PEG particles. Growth factors can be incorporated into these scaffolds by mixing the reconstituted growth factor with the particles prior to sintering. The ability of the PLGA/PEG scaffolds to deliver BMP-2 in a controlled and sustained manner was assessed and the osteogenic potential of these scaffolds was determined in a mouse calvarial defect model. BMP-2 was released from the scaffolds in vitro over 3 weeks. On average, ca. 70% of the BMP-2 loaded into the scaffolds was released by the end of this time period. The released BMP-2 was shown to be active and to induce osteogenesis when used in a cell culture assay. A substantial increase in new bone volume of 55% was observed in a mouse calvarial defect model for BMP-2-loaded PLGA/PEG scaffolds compared to empty defect controls. An increase in new bone volume of 31% was observed for PLGA/PEG scaffolds without BMP-2, compared to empty defect controls. These results demonstrate the potential of novel PLGA/PEG scaffolds for sustained BMP-2 delivery for bone-regeneration applications.