Regenerative Living 4D Printing via Reversible Growth of Polymer Networks

Living creatures possess complex geometries, exceptional adaptability, and continuous growing and regenerating characteristics, which are difficult for synthetic materials to imitate simultaneously. A living polymer network with these features is reported. The polymer can be digitally printed into arbitrary 3D shapes and subsequently undergoes growth via living polymerization of a monomer as the nutrient. This leads to macroscopic dimensional growth and transforms the printed amorphous network into a crystallizable network, resulting in geometric adaptability via a shape‐memory mechanism. By controlling the localized growth, an initial homogeneous structure can be converted into a geometrically different heterogeneous structure composed of materials with different properties (crystallization and mechanical properties). After growth, the original network can be chemically regenerated for regrowth. With this regenerative living 4D printing, one 3D‐printed seed template can be turned into different derivatives with distinct geometries and mechanical properties when repeated regeneration is conducted in different localized regions and the degree of regrowth is varied. This work is inspired by an “immortal” jellyfish, Turritopsis nutricula. A mature T. nutricula has the ability to rejuvenate under unusual circumstances. A regenerative living 4D printable material system is designed. After printing, the printed seed with complex geometries can not only grow by absorbing external monomers (nutrients), but also degrow to its original seed state.