Exosome-integrated titanium oxide nanotubes for targeted bone regeneration

Exosomes are extracellular nanovesicles that play an important role in cellular communication. The modulatory effects of bone morphogenetic protein 2 (BMP2) on macrophages have encouraged the functionalization of scaffolds through the integration of the exosomes from the BMP2-stimulated macrophages to avoid ectopic bone formation and reduce adverse effects. To determine the functionality of exosomal nanocarriers from macrophages after BMP2 stimulation, we isolated the exosomes from Dulbecco's modified Eagle's medium (DMEM)- or BMP2-stimulated macrophages and evaluated their effects on osteogenesis. Morphological characterization of the exosomes derived from DMEM- or BMP2-treated macrophages revealed no significant differences, and the bone marrow-derived mesenchymal stromal cells showed similar cellular uptake patterns for both exosomes. In vitro study using BMP2/macrophage-derived exosomes indicated their beneficial effects on osteogenic differentiation. To improve the bio-functionality for titanium implants, BMP2/macrophage-derived exosomes were used to modify titanium nanotube implants to favor osteogenesis. The incorporation of BMP2/macrophage-derived exosomes dramatically increased the expression of early osteoblastic differentiation markers, alkaline phosphatase (ALP) and BMP2, indicative of the pro-osteogenic role of the titanium nanotubes incorporated with BMP2/macrophage-derived exosomes. The titanium nanotubes functionalized with BMP2/macrophage-derived exosomes activated autophagy during osteogenic differentiation. In conclusion, the exosome-integrated titanium nanotube may serve as an emerging functional material for bone regeneration. Statement of Significance The clinical application of bone morphogenetic protein 2 (BMP2) is often limited by its side effects. Exosomes are naturally secreted nanosized vesicles derived from cells and play an important role in intercellular communication. The contributions of this study include (1) the demonstration of the potential regulatory role of BMP2/macrophage-derived exosomes on the osteogenic differentiation of mesenchymal stromal cells (MSCs); (2) fabrication of titanium nanotubes incorporated with exosomes; (3) new insights into the application of titanium nanotube-based materials for the safe use of BMP2. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.