Versatile click alginate hydrogels with protease-sensitive domains as cell responsive/instructive 3D microenvironments

Abstract

Alginate (ALG) is a widely used biomaterial to create artificial extracellular matrices (ECM) for tissue engineering. Since it does not degrade in the human body, imparting proteolytic sensitivity to ALG hydrogels leverages their properties as ECM-mimics. Herein, we explored the strain-promoted azide-alkyne cycloaddition (SPAAC) as a biocompatible and bio-orthogonal click-chemistry to graft cyclooctyne-modified alginate (ALG-K) with bi-azide-functionalized PVGLIG peptides. These are sensitive to matrix metalloproteinase (MMP) and may act as crosslinkers. The ALG-K-PVGLIG conjugates (50, 125, and 250 μM PVGLIG) were characterized for peptide incorporation, crosslinking ability (double-end grafting), and enzymatic liability. For producing cell-permissive multifunctional 3D matrices for dermal fibroblast culture, oxidized ALG-K was grafted with PVGLIG and with RGD peptides for cell-adhesion. SPAAC reactions were performed immediately before cell-laden hydrogel formation by secondary ionic-crosslinking, considerably reducing the steps and time of preparation. Hydrogels with intermediate PVGLIG concentration (125 μM) presented slightly higher stiffness while promoting extensive cell spreading and higher degree of cell-cell interconnections, likely favored by cell-driven proteolytic remodeling of the network. The hydrogel-embedded cells were able to produce their own pericellular ECM, expressed MMP-2 and 14, and secreted PVGLIG-degrading enzymes. By recapitulating key ECM-like features, these hydrogels provide biologically relevant 3D matrices for soft tissue regeneration.