Mechanical and cellular changes during compaction of a collagen-sponge-based corneal stromal equivalent

The need for corneas suitable for transplantation, combined with the decreasing supply, has fueled interest in the development of a corneal replacement. In this Study, a collagen-spongebased stromal equivalent, consisting of human corneal fibroblasts cultured on a type I collagen sponge, was maintained in culture for up to 21 days and characterized with respect to mechanical properties and cellular behavior. The Young's modulus of the stromal equivalent varied from 95 to 370 Pa, and its permeability varied from 5.3 x 10(-8) -4.2 x 10(-7) m(4) N-1 s(-1). The greatest changes occurred during the first few days in culture, but the mechanical properties continued to change during the entire 2 1 days. Cell traction stress, determined from sponge compaction and DNA count, decreased during the compaction process with the maximum traction value the initial value of 6.6 +/- 12.9 x 10(-3) Pa cm(-1) cell(-1). Microarray data showed that the expression level of fibronectin, decorin sulfate, collagenase, and gelatinase A was upregulated at day 14 in the sponge. This suggested that the repair fibroblast phenotype was being expressed by the fibroblasts. Additional analysis suggested that a subpopulation of cells expressed the myofibroblast phenotype.