A Biocompatible and Self-Healable 3D-Printed Bidirectional Hydrogel Actuator with Needle Injectability

High Resolution Image Download MS PowerPoint Slide Multifunctional hydrogels are highly desirable for emerging material applications, particularly for biocompatible hydrogel actuators. However, integrating toughness, self-healing, and reversible bidirectional actuation into a biocompatible actuator remains challenging. Herein, a 3D-printable and biocompatible bilayer hydrogel actuator with reversible bidirectional actuation is developed using a new poly( N -isopropylacrylamide)-gelatin methacryloyl (PNIPAM-GelMA; “PNG”) hydrogel as the active layer. The photo-cross-linked PNG hydrogel shows self-healing ability as well as good elasticity (storage modulus ∼13 kPa) and toughness (linear viscoelastic range up to 240% shear strain). Small-angle X-ray scattering analysis for the microstructure of PNG reveals the presence of dynamic PNIPAM clusters composed of interlocking PNIPAM side chains, accounting for the self-healing behavior of the PNG hydrogel. The 3D-printed bilayer actuator with PNG as the active layer and GelMA as the passive layer exhibits bidirectional actuation and fine needle injectability. Moreover, pairing the PNG active layer with a self-healable passive layer (e.g., polyurethane-GelMA composite hydrogel) gives rise to a self-healable actuator. This actuator, repaired upon cutting, retains significant bidirectional bending angles (∼380° at 37 °C; ∼−270° at 25 °C). The multifunctional PNG system effectively addresses key limitations of current biocompatible hydrogel actuators by integrating toughness, autonomous self-healing ability, and reversible bidirectional actuation, offering substantial progress in developing actuators for biomedical applications.