Annulus fibrosus tissue engineering using lamellar silk scaffolds

Degeneration of the intervertebral disc (IVD) represents a significant muscular skeletal disease. Recently, scaffolds composed of synthetic, natural and hybrid biomaterials have been investigated as options to restore the IVD; however, they lack the hallmark lamellar morphological features of annulus fibrosus (AF) tissue. The goal of regenerating the disc is to achieve anatomical morphology as well as restoration of mechanical and biological function. In this study, two types of scaffold morphology formed from silk fibroin were investigated towards the goal of AF tissue restoration. The first design mimics the lamellar features of the IVD that are associated with the AF region. The second is a porous spongy scaffold that serves as a control. Toroidal scaffolds were formed from the lamellar and porous silk material systems to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm and a height of 3 mm. The inter-lamellar spacing in the lamellar scaffold was 150-250 µm and the average pore sizes in the porous scaffolds were 100-250 µm. The scaffolds were seeded with porcine AF cells and, after growth over defined time frames in vitro, histology, biochemical assays, mechanical testing and gene expression indicated that the lamellar scaffold generated results that were more favourable in terms of ECM expression and tissue function than the porous scaffold for AF tissue. Further, the seeded porcine AF cells supported the native shape of AF tissue in the lamellar silk scaffolds. The lamellar silk scaffolds were effective in the formation of AF-like tissue in vitro.