Repairing Sequence-Induced Defects in Charge-Imbalanced Polyampholyte Hydrogels

Polyampholyte (PA) hydrogels, composed of cationic and anionic segments, are widely used in wearable device and brain-robot-interface. However, their structural stability is highly sensitive to anionic-to-cationic ratio, presenting challenges in achieving stability and robustness through trial-and-error experimental approaches. This work investigates sequence structures of PA hydrogels, revealing that deviations from ideal charge balance (anion fraction, f = 0.5) introduce sequence-induced defects, characterized by mismatched ionic segments, which significantly influences swelling behavior and mechanical performance. Such structure defects were effectively eliminated by introducing Fe3+, allowing PA gels to maintain stable mechanical properties across a broad f range (0.51-0.58), comparable to those of finely charge-balanced gels. FTIR and viscoelastic analyses suggest that Fe3+ coordination strengthens weak ionic bonds derived from sequence mismatches, enhancing the toughness of charge-imbalanced PA hydrogels. This work provides insights into the origin of internal defects and proposes a new approach for improving hydrogel stability through targeted defect mitigation.