Recyclable 3D printable single network granular hydrogels

Spherical microgels can be conveniently direct ink written into granular hydrogels because of their rheological properties when jammed. Yet, due to weak interparticle interactions, the resulting granular hydrogels are soft and often disassemble if immersed in aqueous media. These shortcomings can be addressed if microgels are firmly connected, for example through inter-particle covalent bonds or by introducing a second hydrogel network that interpenetrates the microgels and covalently connects them. However, these techniques typically hamper the recycling of the granular system. Here, electrostatic attraction forces between microgels and a polyelectrolyte are explored to directly print charged microgels into free standing structures in aqueous media. The resulting granular system remains stable in aqueous media for at least one month and can be recycled with minimal energy input.