Self-healing hydrogels ease into production

Hydrogels are semi-solid materials formed by polymer chains that trap water molecules into three-dimensional gels.

They are used in a variety of applications, including soft contact lenses, but the fragile nature of the materials means that their utility has remained limited. Yasuhiro Ishida, Takuzo Aida and colleagues at the RIKEN Center for Emergent Matter Science are challenging this limitation by developing strong hydrogels, or 'aqua materials', that could outperform even conventional plastics. As part of an international collaboration, the team has now improved the production of a robust, moldable hydrogel that heals itself rapidly after being sliced open.

The RIKEN team previously developed a hydrogel containing three primary ingredients: tiny flakes or 'nanosheets' of anionic clay, an exfoliating chemical that keeps the nanosheets from agglomerating and a polymer binder containing positively charged guanidinium cations.

Mixing small amounts of these substances into a beaker containing water causes a self-standing gel to form within seconds due to cross-linking interactions between the clay nanosheets and the polymer binder. Since the hydrogel is held together by hydrogen bonding and electrostatic forces instead of permanent chemical bonds, if cut open it can be repaired by simply pressing the gel back together.