Influence of macroporous protein scaffolds on bone tissue engineering from bone marrow stem cells

The aim of this study was to investigate the effect of three-dimensional silk fibroin scaffold preparation methods (aqueous and solvent) on osteogenic responses by human bone marrow stem cells (hMSCs). Macroporous 3D protein scaffolds with similar sized pores of 900+/-50 microm were prepared either by an organic solvent process (hexafluoro-2-propanol, HFIP) or an aqueous process. hMSCs were expanded, seeded on the scaffolds, and cultured up to 28 days under static conditions in osteogenic media. hMSCs seeded onto the water-based silk scaffolds showed a significant increase in cell numbers (p<0.01) vs. the HFIP-prepared silk scaffolds. Significantly higher (p<0.01) alkaline phosphatase (ALPase) activity and calcium deposition were apparent after 28 days of culture in the water-based silk scaffolds when compared to the HFIP-derived silk scaffolds. Transcript levels for collagen type I (Col I), ALP, and osteopontin (OP) increased (p<0.05) in the water-based silk scaffolds in comparison to the HFIP-derived materials. At early stages of culture, increased expression of OP and collagen type II (Col II) were also observed in both scaffolds. Expression of Col II, MMP 13, Col I, and OP proteins increased in the water-based silk scaffolds in comparison to the HFIP-derived scaffolds while bone sialoprotein (BSP) proteins increased in the HFIP-derived silk scaffolds in comparison to the water-based scaffolds after 28 days of culture. Histological analysis showed the development of bone-like trabeculae with cuboid cells in an extracellular matrix (ECM) in the water-based silk scaffolds with more organization than in the HFIP-derived material after 28 days of culture. Alcian blue staining demonstrated the presence of proteoglycan in the ECM formed in the water-based scaffolds but not in the HFIP-prepared silk scaffolds. The results suggest that macroporous 3D aqueous-derived silk fibroin scaffolds provide improved bone-related outcomes in comparison to the HFIP-derived systems. These data illustrate the importance of materials processing on biological outcomes, as the same protein, silk fibroin, was used in both preparations.