Self-Healable Antifreeze Hydrogel Based on Dense Quadruple Hydrogen Bonding

The random amphiphilic copolymers containing a large fraction (35–50 mol %) of ureidopyrimidinone (UPy) that can dimerize using a quadruple hydrogen bonding were synthesized to produce antifreeze and dynamic hydrogels. Directional packing of the UPy–UPy dimers provides nanosized aggregates, and the effective gap distance between the aggregates is narrow enough to inhibit the water crystallization by the confinement effect. The characteristic dimensions such as the aggregate size and gap distance depend on the polymer concentration and the UPy fraction in the polymers. Furthermore, the temperature-dependent dynamics of UPy allows the hydrogels to form the frozen structure at a lower temperature, while the injectability and self-healing property were achieved at room temperature. The antifreeze hydrogels also exhibit negligible cytotoxicity and thus expands the applicable area including the drug storage and cell cryopreservation.