A pH-induced self-healable shape memory hydrogel with metal-coordination cross-links

A simple strategy is provided to construct self-healable shape memory hydrogels, which were crosslinked by both dynamic reversible metal-ligand coordination bonds and irreversible covalent bonds. Inspired by the cuticles of marine mussel byssi, hydrogels were fabricated from four-armed poly(ethylene glycol) modified with dopamine end groups with Fe3+ ions. Mono-, bis-and tris-catechol-Fe3+ coordination can be reversibly adjusted by changing the pH value, which could act as a switch for fixing the temporary shape and recovering the original shape. The hydrogels also show the self-healing ability, contributing to the dynamic metal-ligand coordination bonds. At different pH values, the hydrogels showed a regulated shape memory property and self-healing property. When the pH value was 9, bis- and triscatechol-Fe3+ coordination (no mono-coordination) existed and hydrogels exhibited excellent selfhealing, shape memory and high mechanical properties. The hydrogels also showed good cytocompatibility with more than 85% of cell viability after co-culturing with endothelial cells for 7 days. Therefore, by integration of catechol-Fe3+ coordination and covalent bonds, we can achieve hydrogels with good mechanical performance and with both self-healing and shape memory properties, which have great potential applications in the biomedical field.