The binding to FN was determined by an inhibition assay. Here, biotinylated heparin (Merck) was injected to yield ~300 RU. The reference was coated with biotinylated lPG as a control surface imitating the linear uncharged heparin architecture. Then, 250 nM FN or 250 nM FN preincubated with the respective polyanion concentration was injected. The response of 250 nM FN was taken as the 100% value. Again, all SPR measurements were conducted in standard HBS-EP buffer. IC50 values were determined by using a logistic fit in Origin 2022 by plotting the response level in % of the control after 178 s (2 s before starting the dissociation) versus the inhibitor concentration.