Electrospun silk-BMP-2 scaffolds for bone tissue engineering

Abstract

Silk fibroin fiber scaffolds containing bone morphogenetic protein 2 (BMP-2) and/or nanoparticles of hydroxyapatite (nHAP) prepared via electrospinning were used for in vitro bone formation from human bone marrow-derived mesenchymal stem cells (hMSCs). BMP-2 survived the aqueous-based electrospinnig process in bioactive form. hMSCs were cultured for up to 31 days under static conditions in osteogenic media on the scaffolds (silk/PEO/BMP-2, silk/PEO/nHAP, silk/PEO/nHAP/BMP-2) and controls (silk/PEO, silk/PEO extracted). Electrospun silk fibroin-based scaffolds supported hMSC growth and differentiation toward osteogenic outcomes. The scaffolds with the co-processed BMP-2 supported higher calcium deposition and enhanced transcript levels of bone-specific markers than in the controls, indicating that these nanofibrous electrospun silk scaffolds were an efficient delivery system for BMP-2. X-ray diffraction (XRD) analysis revealed that the apatite formed on the silk fibroin/BMP-2 scaffolds had higher crystallinity than on the silk fibroin scaffold controls. In addition, nHAP particles were incorporated into the electrospun fibrous scaffolds during processing and improved bone formation. The coexistence of BMP-2 and nHAP in the electrospun silk fibroin fibers resulted in the highest calcium deposition and upregulation of BMP-2 transcript levels when compared with the other systems. The results suggest that electrospun silk-fibroin-based scaffolds are potential candidates for bone tissue engineering. Furthermore, the mild aqueous process required to spin the fibers offers an important option for delivery of labile cytokines and other components into the system.