Cell adhesion to surfaces has applications in biomaterials science, surface chemistry, and micropatterning technologies. Control of this process is currently achieved using a limited set of molecules, including fibronectin and its derived peptide RGD. Here, we use recombinant strategies to create multivalent, monodisperse polypeptides containing up to 80 repeats of RGD. By varying the number of repeats, we are able to tune the adhesion of cells to surfaces. Cells on these modified surfaces further showed strong resistance to cell delamination under fluid shear forces in a microfluidic channel.