The purpose of this study was to compare the ability of primary human corneal stromal cells (HuFib cells) and SV40-immortalized human corneal keratocytes (HCK cells) to synthesize their own extracellular matrix induced by vitamin C supplementation. Therefore, the amount of collagen secreted and resulting biomechanical properties based on the culture duration were assessed. Cells were cultivated for several weeks with or without vitamin C. The amount of collagen secreted by the cells was quantified based on the culture duration. Cell viability was simultaneously determined via the MTT assay. Collagen secretion was increased as a result of vitamin C supplementation. The effect was stronger in primary cells. In addition, vitamin C supplementation had a positive effect on HuFib cell viability. Vitamin C supplementation induced the formation of detachable cell sheets in both primary and immortalized cells. The biomechanical properties of the sheets were evaluated using a static material testing machine, and the ultrastructure of the cell sheets was examined using scanning electron microscopy. The cell sheets formed from HuFib cells had a higher percentage of light transmission between 400 and 800 nm and were superior in terms of E-modulus and ultimate strength testing. Indirect immunofluorescence and Western blot confirmed the presence of collagen type I in the HuFib and HCK cell cultures. Stimulating secretion of the extracellular matrix in corneal stromal cells is a promising approach for corneal stroma reconstruction for tissue engineering applications.

Ocular surface disorders, such as pterygium, cicatricial pemphigoid and external disruptions, can cause severe inflammation, scarring, fornix shortening as well as ankyloblepharon. Current treatments do not resolve these conditions sufficiently. The aim of this study was to evaluate clinical applicability and suitability of plastic compressed collagen to serve as a substrate for the expansion of human conjunctival epithelial cells in order to develop an epithelialized conjunctival substitute for fornix reconstruction. Human conjunctival epithelial cells were expanded on plastic compressed collagen gels. Epithelial cell characteristics were evaluated by haematoxylin and eosin staining, electron microscopy and cytokeratin expression. The expression of putative epithelial progenitor cell markers p63α, ABCG2 and CK15 was assessed by immunostaining. The proliferative capacity and clonal growth of the cells was evaluated before (P0) and after expansion (P1) on the plastic compressed collagen gels by colony forming efficiency assay. The potential clinical applicability of this gel substitutes was evaluated by assessment of their biomechanical properties as well as their surgical handling. Human conjunctival epithelial cells cultured on plastic and plastic compressed collagen gels formed a confluent cell layer and expressed CK19. The cells showed expression of the putative epithelial progenitor cell markers p63α, ABCG2 and CK15 and sustained colony forming ability. The compressed collagen gels showed a high ultimate tensile strength and elasticity and the surgical handling of gels was comparable to amniotic membrane. An epithelialized conjunctival tissue construct on the basis of compressed collagen might therefore be a promising alternative bioartificial tissue substitute for conjunctival reconstruction.

We conclude that in contrast to clinical applications, the riboflavin/UVA treatment does not seem to be a suitable method to obtain a sufficiently firm stromal matrix including vital keratocytes to build a tissue-engineered human cornea construct to be used as an in vitro model for drug absorption studies.

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