High‐Resolution 3D Printing of Stretchable Granular Hydrogel Filaments for Fabricating Robust and Durable Tissue Phantoms with Tunable Mechanical Strength

Granular hydrogels are a promising class of 3D-printable inks but often suffer from low printing resolution due to large microgel sizes (>100 µm) and weak mechanical performance from lower packing density. To overcome these limitations, a novel whey protein microgels-based granular hydrogel (WMGH) is developed, consisting of uniform, size-controllable microgels (1, 6, and 20 µm) via protein-polysaccharide segregative phase separation. The smaller microgels enable WMGH to stretch like continuous liquid inks by adjusting printing speed and pressure, achieving high-resolution 3D-printing (200 µm) with minimal ink spreading (≈5%) using a 25G nozzle (260 µm). This allows the fabrication of intricate structures like human ear and aortic valve models. Incorporating a polyacrylamide (PAM) second percolating network transforms WMGH inks into double-network hydrogels (DN-WMGH), showing up to 36 fold increase in toughness (1.45 MJ m^{- 3}) compared to PAM hydrogels. Controlling microgel size provides a new approach for tailoring mechanical strength (6-300 kPa) while maintaining durability, exhibiting full recovery after 100 tensile cycles at 100% strain. DN-WMGH from biopolymers demonstrated good compatibility. This high-resolution 3D-printing of robust DN-WMGH replicates the mechanical properties of various tissues, from brain (<10 kPa) to intestine (≈300 kPa), demonstrating new possibilities for tissue-mimicking applications in surgical training, implantable devices, and drug-delivery systems.