INFLUENCE OF THE SUBSTRATE BINDING CHARACTERISTICS OF FIBRONECTIN ON CORNEAL EPITHELIAL-CELL OUTGROWTH

The outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. Circular corneal buttons (5 mm) were punched from excised rabbit corneas and placed onto bare substrates or substrates preadsorbed with fibronectin (fn), albumin, or binary mixtures of both fn and albumin. Cell outgrowth areas were measured after culturing the buttons for 4 days in serum-free medium. Fibronectin adsorption to the materials was measured from pure and binary solutions with I-125-radiolabeled fibronectin. A parameter thought to be related to the binding strength of fn to polymeric substrates was measured in parallel experiments by partial elution of the adsorbed fn by 3% sodium dodecyl sulfate (SDS). Following pure solution fibronectin adsorption a range of outgrowth areas was measured (from 0.86 +/-0.03 cm2 for glass to 1.49 +/- 0.03 cm2 for TCPS). On all of the materials tested cell outgrowth areas increased following fn preadsorption and decreased following albumin preadsorption relative to bare surfaces (p < 0.05). Following preadsorption with binary protein mixtures cell outgrowth areas increased with fibronectin adsorption, however, the outgrowth areas were not determined solely by the concentration of fn adsorbed onto the surfaces. This result suggested that the biological efficiency of the adsorbed fibronectin was substrate-dependent. When the cell outgrowth data were cross-plotted against fn retention following SDS elution, the outgrowth areas were found to increase along with increases in fn retention. Based on these data we suggest that epithelial cell outgrowth may be partially governed by the tightness of binding between the fn molecules and the underlying substrate.