Bifunctional Poly(acrylamide) Hydrogels through Orthogonal Coupling Chemistries

Biomaterials for cell culture allowing simple and quantitative presentation of instructive cues enable rationalization of the interplay between cells and their surrounding microenvironment. Poly(acrylamide) (PAAm) hydrogels are popular 2D-model substrates for this purpose. However, quantitative and reproducible biofunctionalization of PAAm hydrogels with multiple ligands in a trustable, controlled, and independent fashion is not trivial. Here, we describe a method for bifunctional modification of PAAm hydrogels with thiol- and amine- containing biomolecules with controlled densities in an independent, orthogonal manner. We developed copolymer networks of AAm with 9% acrylic acid and 2% N-(4-(5-(methylsulfonyl)-1,3,4-oxadiazol-2-yl)phenyl)acrylamide. The covalent binding of thiol- and amine-containing chromophores at tunable concentrations was demonstrated and quantified by UV spectroscopy. The morphology, mechanical properties, and homogeneity of the copolymerized hydrogels were characterized by scanning electron microscopy, dynamic mechanical analysis, and confocal microscopy studies. Our copolymer hydrogels were bifunctionalized with polylysine and a laminin-mimetic peptide using the specific chemistries. We analyzed the effect of binding protocol of the two components in the maturation of cultured postmitotic cortical neurons. Our substrates supported neuronal attachment, proliferation, and neuronal differentiation. We found that neurons cultured on our hydrogels bifunctionalized with ligand-specific chemistries in a sequential fashion exhibited higher maturation at comparable culture times than using a simultaneous bifunctionalization strategy, displaying a higher number of neurites, branches, and dendritic filopodia. These results demonstrate the relevance of quantitative and optimized coupling chemistries for the performance of simple biomaterials and with sensitive cell types.