Bioengineering Organized, Multilamellar Human Corneal Stromal Tissue by Growth Factor Supplementation on Highly Aligned Synthetic Substrates

Recapitulating the microstructure of the native human corneal stromal tissue is believed to be a key feature in successfully engineering the corneal tissue. The stratified multilayered collagen fibril lamellae with orthogonal orientation determine the robust biomechanical properties of this tissue, and the uniform collagen fibril size and interfibrillar spacing are critical to its optical transparency. The objective of this investigation was to develop a highly organized collagen-fibril construct secreted by human corneal stromal stem cells (hCSSCs) to mimic the human corneal stromal tissue. In culture on a highly aligned fibrous substrate made from poly(ester urethane) urea, the fibroblast growth factor-2 (FGF-2, 10 ng/mL) and transforming growth factor-beta 3 (TGF-β3, 0.1 ng/mL) impacted the organization and abundance of the secreted collagen fibril matrix. hCSSCs differentiated into keratocytes with significant upregulation of the typical gene markers, including KERA, B3GnT7, and CHST6. FGF-2 treatment stimulated hCSSCs to secrete collagen fibrils strongly aligned in a single direction, whereas TGF-β3 induced collagenous layers with orthogonal fibril orientation. The combination of FGF-2 and TGF-β3 induced multilayered lamellae with orthogonally oriented collagen fibrils, in a pattern mimicking the human corneal stromal tissue. The constructs were 60-70 μm thick and had an increased content of cornea-specific extracellular matrix components, including keratan sulfate, lumican, and keratocan. The approach of combining substrate cues with growth factor augmentation offers a new means to engineer well-organized, collagen-based constructs with an appropriate nanoscale structure for corneal repair and regeneration.