Mutifunctional Ion Pairs (MFIPs) Enable Topologically Regular Ion-Mediated Dynamic Gels

Ion-mediated gels formed by phase-separated polyelectrolyte coacervates or polyampholytes have emerged as intriguing materials with desirable properties, including on-demand degradation, processability, and self-healing. However, their behavior is dictated by several interconnected factors, including ion chemistry, topology, stoichiometry, and environment. Thus, the rational design of ion-mediated gels remains a challenge. Here, we develop a model system in which non-ionic poly(ethylene glycol) (PEG) star polymers are connected utilizing pre-associated multifunctional ion pairs (MFIPs) via thiol-ene ‘click’ chemistry. This approach decouples phase separation from gelation, enabling the formation of ion-mediated gels with highly controlled topology and stoichiometry. By adjusting MFIP functionality or the number of ion pairs, we can readily tune gel moduli and relaxation times by over an order of magnitude without needing to alter macromer chemistry. Notably, MFIP gels exhibit a single terminal relaxation (atypical of ionically bonded materials with random connectivity) due to the regular topology of dynamic ionic crosslinks. Moreover, the use of UV light as a trigger for gelation enables photopatterned gels using projection lithography; a functionality difficult to design into ion-mediated materials. As such, MFIP gels represent a paradigm shift in ion-mediated dynamic materials, empowering programmable and highly controlled gel properties.