Chemically-induced Jamming and 3D printing of Granular Hydrogels: Microgels as Reservoirs of Volume

Granular hydrogels, composed of jammed soft microparticles, have garnered significant attention for 3D (bio)printing due to their ideal rheological properties and extensive modularity, resulting in favorable microstructures for tissue engineering. The yield-stress properties of these materials, which enhance printability, are primarily determined by the preparation state and initial particle content of the hydrogel.

This study introduces a granular hydrogel whose yield-stress, printability, and printed scaffold shape retention can be manipulated not only by the initial particle weight fraction but also by their stimuli-responsive swelling characteristics. The responsive microgels are synthesized from poly(N-isopropylacrylamide) crosslinked by dynamic covalent disulfide bonds.

Upon reduction-induced cleavage of the disulfide bonds, the particles swell, allowing the printing of multilayer scaffolds with exceptional shape fidelity. In the absence of chemically induced swelling, achieving the same printability necessitates higher particle concentrations. Remarkably, the printed structures can be annealed by oxidizing the thiol units back into disulfide inter-particle bonds.

These printed scaffolds demonstrate compatibility with human dermal fibroblasts (HDF), supporting cell-material interactions. This innovative system provides a novel method for on-demand modulation of printability and scaffold microstructure, enabling precise control over local stiffness, packing density, and porosity within granular scaffolds.