In Situ Topology Change of Polymer Networks Induces Rapid Hydrogelation and Enables Pathway-Dependent Reinforcement in Double Networks

The incorporation of deformable network junctions into polymer networks is a new fundamental concept in the design of smart topology-switching materials. However, it is still a nascent field that needs to be amplified by developing new deformable junctions and creating materials with practical properties. Here, we construct a new topology-switching polymer network (TPN) by using conformational transformable peptide coiled-coils as deformable network junctions. The coiled-coil junctions display two distinct branch functionalities at pH 6 and pH 8, respectively. As a consequence, the TPN shows a nearly instantaneous and reversible solution-gel transition when the pH varies between 6 and 8. This transition does not rely on the establishment of interactions between the polymer components that occurs during most hydrogelation processes but only on the reconfiguration of the polymer network triggered by topology change, which may represent a new hydrogel formation mechanism. Moreover, the TPN can be used as the minor network to reinforce the main network in a double network system, but unexpectedly and interestingly, the reinforcement is pathway-dependent and can only be achieved by the in situ topology change of TPN in a double network rather than directly utilizing the TPN with a specific topology to prepare the double network.