During development glycosoaminoglycans (GAG), especially heparan sulfate (HS), act as critical regulators of growth factor signaling like that of bone morphogenetic proteins (BMPs) and Indian hedgehog (Ihh), both regulators of skeletal development. The exact mechanisms by which HS controls signal presentation, distribution and activation are not well understood. Recent studies indicate the existence of a HS sulfation code that is recognized by distinct surface domains of proteins. Besides binding to HS some growth factors also bind to the GAG Chondroitin sulfate (CS), but with lower affinity. In this project we aim to decipher the specificities of growth factor–GAG interaction using biomimetic platforms presenting immobilized GAGs. These platforms permit to control the relative surface concentration and binding affinities between growth factors and GAGs. The impact of the binding modalities will be tested in in biological systems including cell culture and tissues of mouse mutants.