Our group has previously reported on successful biofunctionalization of poly(ethylene glycol diacrylate) (PEGDA) gels using chondroitin sulfate (CS) and improving moduli of methacrylated-CS (MCS) gels using short PEGDA comonomers. Here, we focused on understanding the composition-property relationship of MCS-PEGDA copolymers. By changing concentration, composition, and medium's ionic strength the gels were modified to show a diverse range of properties. Photopolymerized copolymers with >4:1 ratio of one component had compressive moduli of up to 24 times higher and up to 17 times lower swelling degree (q) than those of MCS alone. The increased moduli and lowered q were consistent with the hypothesis that PEGDA improves kinetic chain growth by overcoming the steric hindrances of the macromer. The swelling and moduli of the gels were tuned by changing the ratio of the comonomers. The swelling and moduli of the gels were lowered with presence of salt in solution while the fracture strain increased. These changes were hypothesized to be the result of transition of CS chain conformation from highly extended and non-Gaussian to less extended and Gaussian distribution. The complete understanding of MCS-PEGDA compositionproperty relationship provides a general strategy to tune the moduli or q of polysaccharide-based hydrogels while avoiding undesirable phase separation. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1070-1079 KEYWORDS: biomaterials; copolymers; hydrogels; mechanical properties; photopolymerization INTRODUCTION The mammalian extracellular matrix (ECM) is a multicomponent, hierarchically ordered structure. Chondroitin sulfate (CS) and hyaluronic acid (HA) are two of the main glycosaminoglycans (GAGs) present in the mammalian ECM. Collagen type II, keratan sulfate, and proteins are other major ECM components. Regeneration of the damaged ECM has been the focus of multiple tissue engineering studies. A common strategy is to replace the damaged matrix with naturally available biomimetic materials. An optimal scaffold to mimic the ECM would be made of multiple components to provide the appropriate balance of mechanical properties, water content, solute permeability, and cell interactions.