Porous silk fibroin 3‐D scaffolds for delivery of bone morphogenetic protein‐2 in vitro and in vivo

Abstract

Bone morphogenetic protein‐2 (BMP‐2) plays a key role in osteogenesis. Biomaterials used for the sustained delivery of BMP‐2 in vivo have shown therapeutic benefits. In the present study, BMP‐2 was loaded in porous silk fibroin scaffolds derived from silkworm cocoons (2.4 ± 0.14 μg per scaffold). The release profile of BMP‐2 under dynamic culture conditions (spinner flasks) showed that after 1 week in culture 25% of the initial BMP‐2 was retained adsorbed to the scaffold; up to 4 weeks no additional BMP‐2 was released. BMP‐2 induced human bone marrow stromal cells (hMSCs) to undergo osteogenic differentiation when the seeded scaffolds were cultured in medium supplemented with osteogenic stimulants for 4 weeks, based on elevated alkaline phosphatase activity, calcium deposition, and transcript levels for bone sialoprotein, osteopontin, osteocalcin, BMP‐2, and cbfa‐1. Micro‐computed tomography revealed densely deposited mineral at the center of the scaffolds. In contrast, hMSCs cultured in control scaffolds (no BMP‐2) exhibited limited osteogenesis. When implanted in critical sized cranial defects in mice, scaffolds loaded with BMP‐2 and seeded with hMSCs resulted in significant bone ingrowth. These results were qualitatively similar to scaffolds loaded with BMP‐2 but no hMSCs or with BMP‐2 and hMSCs but not pregrown into bone‐like tissue. Bone‐related outcomes were improved when compared with the scaffold controls implanted without BMP‐2. These studies illustrate the potential use of slow degrading silk fibroin 3‐D scaffolds loaded with BMP‐2, in combination with hMSCs, in osteogenesis studies in vitro and in vivo, and provide a new range of material properties for these applications. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006