Peptide-Functionalized Click Hydrogels with Independently Tunable Mechanics and Chemical Functionality for 3D Cell Culture

Click chemistry offers highly selective and orthogonal reactions that proceed rapidly and under a variety of mild conditions with the opportunity to create highly defined and multifunctional materials. This work illustrates a strategy where step-growth networks are formed rapidly via a copper-free, azide-alkyne click chemistry between tetrafunctional poly(ethylene glycol) molecules and difunctionalized synthetic polypeptides. The molecular weight of the polymer precursors (10, 15, or 20 kDa PEG) and the stoichiometry of reactive end group functionalities (1.5:1 to 1:1.5) provide control over the material cross-linking density, enabling elastic materials with tunable moduli (G' = 1000-6000 Pa). A sequential photochemically activated thiol-ene chemistry allows subsequent functionalization of the network through reaction with pendant alkene moieties on the peptide. Because the thiol-ene reaction is light-driven, the degree of modification is directly related to the dosage of light delivered to the system (0-6 J cm(-2)). We exploit this feature to create complex biochemical gradients of multiple peptides with well-defined magnitude and slope throughout the three-dimensional (3D) network. Since both reactions can occur in the presence of cells, this material ultimately enables independent and in situ tuning of biochemical and biomechanical properties of biomaterial networks, suggesting an avenue to direct cell function throughout specific regions within a 3D material.