In this study, we have demonstrated that the modification of hyaluronan (hyaluronic acid; Hya) with sulfate groups led to different binding affinities for recombinant human bone morphogenetic protein-4 (rhBMP-4). The high-sulfated sHya2 8 (average degree of sulfation (D S.) 2.8) exhibited the tightest interaction with rhBMP-4, followed by the low-sulfated sHya 1.0, as determined with surface plasmon resonance (SPR), ELISA, and competition ELISA. Unmodified Hya, chondroitin-sulfate (CS), and heparan sulfate (HS) showed significantly less binding affinity. SPR data could be filled to in A + B = AB Langmuir model and binding constants were evaluated ranging from 13 pM to 5.45 mu M. The interaction characteristics of the differentially sulfated Hyas are promising for the incorporation of these modified polysaccharides in bioengineered coatings of biomaterials for medical applications