A Biomimetic Bilayer Hydrogel Actuator Based on Thermoresponsive Gelatin Methacryloyl-Poly(N-isopropylacrylamide) Hydrogel with Three-Dimensional Printability

Development of hydrogel-based actuators with programmable deforma-tion is an important topic that arouses much attention in fundamental and applied research. Most of these actuators are nonbiodegradable or work under nonphysiological conditions. Herein, a temperature-responsive and biodegradable gelatin methacryloyl (GelMA)-poly(N-isopropylacrylamide) hydrogel (i.e., GN hydrogel) network was explored as the active layer of a bilayer actuator. Small-angle X-ray scattering (SAXS) revealed that the GN hydrogel formed a mesoglobular structure (similar to 230 angstrom) upon a thermally induced phase transition. Rheological data supported that the GN hydrogel possessed 3D printability and tunable mechanical properties. A bilayer hydrogel actuator composed of active GN and passive GelMA layers was optimized by varying the layer thickness and compositions to achieve large, reproducible, and anisotropic bending with a curvature of similar to 5.5 cm-1. Different patterns of the active layer were designed for actuation in programmable control. The 3D printed GN hydrogel constructs showed significant volume reduction (similar to 25-60% depending on construct design) at 37 degrees C with the resolution enhanced by the thermo-triggered actuation, while they were able to fully reswell at room temperature. A more intricate 3D printed butterfly actuator demonstrated the ability to mimic the wing movement through thermoresponsiveness. Furthermore, myoblasts laden in the GN hydrogel exhibited significant proliferation of similar to 376% in 14 days. This study provides a new fabrication approach for developing biomimetic devices, artificial muscles, and soft robotics for biomedical applications.

Automated summary

The development of hydrogel-based actuators with programmable deformation has attracted much attention in both fundamental and applied research. In this study, a temperature-responsive and biodegradable gelatin methacryloyl (GelMA)-poly(N-isopropylacrylamide) hydrogel (GN hydrogel) was explored as the active layer of a bilayer actuator. The optimized bilayer hydrogel actuator exhibited large, reproducible, and anisotropic bending, and has potential applications in biomimetic devices, artificial muscles, and soft robotics for biomedical purposes.