Cell culture substrates presenting a heparin-binding peptide sequester heparin from serum and, in turn, amplify recombinant growth factor activity. A) 3-D rendition of a heparin tetrasaccharide (red) binding to HEPpep, which is derived from FGF-2 (HEPpep is green, the rest of the FGF-2 protein is blue). PDB accession number 1BFB. B) A SAM presenting a heparin-binding peptide (green) sequesters a growth factor (blue) in the presence of serum-borne heparin (red), and presents the growth factor to cell surface receptors, resulting in amplified growth factor activity.