3D printing of granular microgels: rheological responses with capillary interactions

Colloids and particle suspensions have served as facile approaches to introduce biological functionalities by loading with bioactive agents. The jamming behaviors of packed granular microgels enable their use as a support medium for 3D printing stable shapes. Unfortunately, the loose interactions among a liquid-particle suspension system result in low self-supporting ability in extrusion-based 3D printing. To address this shortcoming, secondary immiscible liquid is introduced into the system, in which particle networks are formed through the capillary bridges, known as capillary suspensions. Rigid particle systems with capillary suspensions have been widely investigated, however, the rheological response of the capillarity-mediated soft particle networks remains to be elucidated. Here, it is demonstrated that the size and stiffness of soft microgels depend on the emulsification method, and their rheological responses can be manipulated in the presence of capillary bridges. These findings offer an in-depth understanding of how soft, deformable microgels can be munufactured into programmable bulk microstructured materials and how the size of microgels and concentrations of capillary liquid affect the rheological response, thus paving a new way for the adjustment of interparticle interaction in soft particle systems.