A Versatile Gradient of Biomolecules for Regulating Cell Behaviour

Interactions between cells and surface-immobilized gradients of biomolecules provide a tool for discerning key parameters that direct cell behaviour. The implementation of a tuneable, grafted polymer scaffold on polystyrene and poly(ethylene terephthalate) is described. This is developed by UV-ozone activation of the surface, followed by in situ 'grafting from' of acrylic acid (AA). Wide ranges of poly(acrylic acid) (pAA) graft densities and lengths are explored by quantifying the surface density of carboxylic acid (–COOH) groups. The reactivity of (–COOH) moieties is used to immobilize streptavidin (SAV), either via covalently bound biotin or by carbodiimide-mediated reaction with (–NH2) moieties. Biotinylated biomolecules, immobilized on SAV, can thus be presented to cultured cells. Immobilized fluorescent SAV and biotin indicate that controlled variations in pAA surface density are translated into tuneable surface density gradients of the immobilized biomolecules. Cyclo-RGD peptide sequences immobilized on the pAA scaffold promote the attachment of cultured murine sarcoma S180 cells, giving rise to higher spreading and motility with higher RGD surface density. This proof-of-concept illustrates how engineered surfaces can provide a simple tool for presenting gradients of biotinylated molecules, which regulate and enable the study of cell-extracellular matrix interactions.