Similarity in Linear Viscoelastic Behaviors of Network Formation and Degradation Processes

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The design of the network formation and degradation processes is required to control hydrogel's life cycle. There have been many studies to optimize both processes of the hydrogel for biomaterials. The conventional studies based on the assumption that the network formation and degradation processes are equivalent. The premise of the similarity is not self-evident, which is difficult to investigate experimentally. It is because of the difficulty in the experimental determination of the connectivity of the network. In this study, we utilized the Tetra gel with slow degradation units to observe a continuous process from network formation to degradation of a single hydrogel. We measured the time-development of the linear viscoelastic properties during the network formation and degradation processes using a single system. The linear viscoelasticity at the same connectivity and the critical points for gelation and degradation well agreed. These results strongly suggest that the network formation and degradation go along the identical path toward the opposite directions. Based on our findings, we propose a simplified criterion for the gelation over the Winter-Chambon criterion based on the observation. These findings will help a basis for the sol-gel transition behavior of the polymer gels.