Top: Cell-instructive characteristics of the extracellular matrix (ECM) governing tissue formation, homeostasis and regeneration. Glycosaminoglycans (GAGs) with different sulfation patterns are a main component of the ECM (orange). The ECM affords adaptable physical properties (viscoelastic properties, black) with structural heterogeneity (grey), allows cell-responsive remodeling (blue), displays adhesion ligands/attachment sites (red) and modulates morphogen signaling (light red). Bottom: GAG-based biomaterials can be instrumental in recapitulating these fundamental ECM features through the molecular design and processing of polymer networks to tune the administration of soluble factors, the network structure, the adhesiveness, the shape and the degradability of the matrices respectively.