Reversible Stiffening of Biopolymeric Hybrid Networks by Dynamically Switching Cross-Links In Situ

Achieving reversible stiffening of biopolymer networks in a controlled manner remains a challenging topic in materials science, especially when trying to assess the following changes in mechanical material properties in real time. To address these challenges, we here utilize a custom-made measurement setup that allows us to manipulate the cross-linking state of alginate-based hydrogels in situ while quantifying the achieved alterations in the viscoelastic response of the biopolymer networks. Interpolymer connections in the biopolymer networks are created by a combination of light-induced, covalent cross-links, ionic cross-links, and DNA-based cross-links, where the latter two can be successfully removed again by employing either chelating agents (e.g., ethylenediaminetetraacetic acid and citrate) or suitable displacement DNA strands. In part, this range of the different cross-linking options mentioned is inter alia made possible by incorporating the glycoprotein mucin into the alginate system, which also allows for a range of different starting (∼0.2–400 Pa), intermediate (∼25 Pa–1.6 kPa), and final stiffnesses (∼4 Pa–1.2 kPa) of the mixed hydrogel matrix. At the same time, the presence of mucins (1–4% (w/v)) in the biopolymer mixture enhances the properties of the cytocompatible hydrogel by improving its antibacterial characteristics. Such well-controllable alginate/mucin networks with dynamically switchable mechanical properties will likely find broad applications in cell cultivation studies or tissue engineering applications.