The engineering of organized human corneal tissue through the spatial guidance of corneal stromal stem cells

Corneal stroma is an avascular connective tissue characterized by layers of highly organized parallel collagen fibrils, mono-disperse in diameter with uniform local interfibrillar spacing. Reproducing this level of structure on a nano- and micro-scale may be essential to engineer corneal tissue with strength and transparency similar to that of native cornea. A substrate of aligned poly(ester urethane) urea (PEUU) fibers, 165 ± 55 nm in diameter, induced alignment of cultured human corneal stromal stem cells (hCSSCs) which elaborated a dense collagenous matrix, 8-10 μm in thickness, deposited on the PEUU substratum. This matrix contained collagen fibrils with uniform diameter and regular interfibrillar spacing, exhibiting global parallel alignment similar to that of native stroma. The cells expressed high levels of gene products unique to keratocytes. hCSSCs cultured on PEUU fibers of random orientation or on a cast film of PEUU also differentiated to keratocytes and produced abundant matrix, but lacked matrix organization. These results demonstrate the importance of topographic cues in instructing organization of the transparent connective tissue of the corneal stroma by differentiated keratocytes. This important information will help with design of biomaterials for a bottom-up strategy to bioengineer spatially complex, collagen-based nano-structured constructs for corneal repair and regeneration.