4D Printing of Self-Healing, Thermally, and Near-Infrared Light-Responsive Granular Hydrogels with Segmental Directed Movement for Soft Robotic

Soft robots with intelligent shape-changing capabilities and spatially controlled actuation are essential for enhancing their performance. Here, three-dimensional printing of self-healing, near-infrared light-responsive shape memory granular hydrogels (SLSH) was introduced. The hydrogels were formulated using four distinct microgels: β-cyclodextrin-functionalized microgels (CDMGs) and 1-adamantylamine-functionalized microgels (AMGs) to promote host–guest physical interactions for self-healing and shear-thinning properties; polydopamine-functionalized microgels (PMGs) for photothermal conversion and antibacterial activity; and microgels with epoxy groups (MG) to enable chemical cross-linking with Jeffamine, forming a shape memory framework. The shear-thinning, shape memory, and self-healing characteristics were influenced by physical interactions within the ink as well as the chemical bonds formed after postprinting treatment. The viscosity and yield strength of the inks showed an increasing trend with a higher fraction of CDMG and AMG, indicating stronger reversible attractions within the jammed assembly of particles. Upon irradiation with an intensity of 1000 mW·cm –2 for 2 min, the internal temperature of the hydrogels increased to 38.2–43.0 °C, depending on the hydrogel type. For SLSH70, a distinct melting peak was recorded at 35–41 °C, associated with the melting of crystalline domains of Jeffamine, which was essential for the thermal shape recovery of the construct. After 1 h of fixation, the hydrogels SLSH30, SLSH50, and SLSH70 demonstrated a shape-fixing efficiency of 98.22 ± 0.45, 99.38 ± 0.68, and 98.54 ± 0.26%, respectively, with shape recovery efficiency approaching approximately 100%. During the self-healing process, complete reattachment occurred after 24 h at 25 °C for SLSH30, while the other samples exhibited a weaker healing ability. Finally, the results of antibacterial investigations highlighted the synergistic effects of PMG’s inherent antibacterial properties and its photothermal activity within the bacterial environment.