Dual-Functionalizable Streptavidin-SpyCatcher-Fused Protein-Polymer Hydrogels as Scaffolds for Cell Culture

Hydrogels possessing the ability to control cell functions have great potential as artificial substrates for cell culture. Herein, we report dual-functionalizable protein-polymer hybrid hydrogels prepared by thiol oxidation catalyzed by horseradish peroxidase and a phenolic molecule. A chimera protein of streptavidin (SA) and the SpyCatcher protein, with a cysteine residue at its N-terminus, (C-SA-SC) was constructed and co-cross-linked with thiol-functionalized four-arm polyethylene glycol (PEG-SH) to obtain hydrogels possessing two orthogonal conjugation moieties. Hydrogel formation using C-SA-SC conjugated with biotinylated or SpyTagged functional molecules (premodification strategy) resulted in the formation of hydrogels with a uniform distribution of the functional molecules. Postmodification of the functional molecules of the C-SA-SC hydrogel with biotin or SpyTag could alter the three-dimensional (3D) spatial distribution of the functional molecules within the hydrogels depending on the mode of conjugation (SA/biotin or SpyCatcher/SpyTag), the size of the functional molecules, and the length of time of the modification. NIH-3T3 cells cultured on a C-SA-SC hydrogel, dual-functionalized with a biotinylated-Arg-Gly-Asp-Ser (RGDS) peptide and a basic fibroblast growth factor (bFGF) with SpyTag, showed cell adhesion to the PEG-SH-based hydrogels and cell morphological changes in response to the immobilized RGDS peptide and the bFGF. Moreover, the cells showed higher proliferation on the dual-functionalized C-SA-SC hydrogel than the cells cultured on hydrogels without either the RGDS peptide or the bFGF, demonstrating the benefits of dual-functionalizable hydrogels. The C-SA-SC hydrogel presented in this study is capable of being orthogonally functionalized by two different functional molecules with different 3D distributions of each molecule within the hydrogel and thus has the potential for use as a cell culturing scaffold for creating artificial cellular microstructures.