Enhancing annulus fibrosus tissue formation in porous silk scaffolds

There is presently no optimal treatment for patients with chronic back pain as a result of degenerative disc disease. Tissue engineering, an annulus fibrosus (AF) construct suitable to repair the damaged AF, is one novel approach to the treatment of this disease. We have previously demonstrated that porous silk scaffolds can support AF cell attachment and extracellular matrix accumulation; however, tissue infiltration and matrix accumulation was not optimal. The purpose of this study was to determine whether the dynamic culture of AF cells seeded into larger average pore size silk scaffolds would improve tissue formation. AF cells were isolated from bovine caudal discs and seeded into porous silk scaffolds and grown in either dynamic or static flow conditions. The cell-seeded scaffolds were grown for up to 4 weeks and evaluated for cell attachment, gene expression, histological appearance, and matrix accumulation. Dynamic culture improved AF tissue formation as the tissue was more cellular and contained significantly more matrix than that formed in static culture. Spatial distribution of tissue was comparable for static and dynamic culture. Varying scaffold pore sizes (200-, 600-, and 1000-microm pore size) demonstrated that an average pore size of 600 microm resulted in the most uniform tissue distribution with the greatest amount of type I collagen. Our study suggests that dynamic flow conditions and scaffold pore size can affect the formation of engineered AF tissue.