A novel hydrogel actuator that combines ionoprinting techniques with reversible catechol-metal ion coordination chemistry found in mussel adhesive proteins was developed. Deposited metal ions increased local crosslinking density, which induced sharp bending of the hydrogel. Reversibly bound metal ions can be removed and reintroduced in a different pattern so that the hydrogel can be reprogrammed to transform into a different 3-dimentional shape.