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

Abstract 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.