Covalent immobilization of RGDS on hydrogel surfaces to direct cell alignment and migration

This study extends the capability for directing cell behavior using PEG-based hydrogels in tissue-engineering applications to include control over the spatial distribution of the adhesive peptide, RGDS. A continuous linear gradient was formed by simultaneously using a gradient maker to combine precursor solutions and using photopolymerization to lock the RGDS gradient in place. Hydrogels containing entrapped gradients of bovine serum albumin (BSA) were characterized using Coomassie brilliant blue stain, which indicated that BSA concentration increases along the hydrogel's length and that the steepness of the gradient's slope can be varied by changing the relative BSA concentrations in the precursor solutions. Human dermal fibroblasts responded to covalently immobilized RGDS gradients by changing their morphology to align in the direction of increasing RGDS concentration. After 24 h, ∼46% of fibroblasts were aligned with the RGDS-gradient axis. This proportion of cells further increased to ∼53% (p < 0.05) and ∼58% after 48 and 96 h, respectively. Also, fibroblasts migrated differentially depending on the concentration of RGDS. Fibroblasts migrated ∼48% further going up the concentration gradient (0 to 6 μmol/ml PEG-RGDS) than going down the concentration gradient. Migration up the concentration gradient was also ∼33% greater than migration on control surfaces with a constant concentration of RGDS (2 μmol/ml), while migration down the gradient was reduced ∼12% relative to the control surface. In addition, directed migration was further enhanced by increasing the RGDS gradient's slope. This hydrogel system is expected to be useful for directing cell migration to enhance the formation of engineered tissues.