Endothelialization of a non-woven silk fibroin net for use in tissue engineering: Growth and gene regulation of human endothelial cells

We have previously shown that a biomaterial consisting of a non-woven fibroin net produced from silk (Bombyx mori) cocoons is an excellent scaffolding material for a wide variety of human cells of different tissue types. Endothelialization must take place for a biomaterial to be successful after implantation. Therefore, primary human endothelial cells and the human endothelial cell lines, HPMEC-ST1.6R and ISO-HAS-1, were examined for adherence and growth patterns on the fibroin nets by confocal laser scanning microscopy after vital staining of the cells and by electron microscopy. Endothelial cells adhered and spread along individual fibers of the nets and did not fill the gaps between individual fibers. Higher attachment and growth coverage was obtained if nets were first coated with gelatin, fibronectin or collagen type I. Proinflammatory markers of endothelial cells on the fibers exhibited a non-activated state and LPS-stimulated cells exhibited activation of these markers. Furthermore, a typical PECAM-1 localization at cell-cell contacts was observed. Scanning electron microscopic examination of fibroin nets after removal of cells did not demonstrate any changes to the fibroin structure. HUVEC and HDMEC on fibroin nets embedded in collagen type I gels formed microvessel-like structures. Thus, silk fibroin nets are a highly endothelial cell-compatible scaffolding material that support the growth, normal and inducible cell functions and angiogenesis potential of human endothelial cells in vitro similar to that observed in vivo.