4D Printed Soft Robot

Abstract

Hydrogels are capable of absorbing large amounts of liquid or biological fluids in three-dimensional polymeric networks. The properties of smart gels can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are kind of smart material that have the ability to demonstrate reversible shape transformation induced by an external stimulus like in our present study: temperature sensitivity. Mechanically strong along with good flexibility and transparency, Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs [1] show thermoresponsive shape memory behavior above 40 °C. DMMA-co-SA SMGs have been fabricated by stereolithographic process using our customized 3D printer named as SWIM-ER. Using SWIM-ER we were able to print sample models like gel sheets, tubes, fingers etc. of SMGs that were transparent, flexible and strong. To successfully print SMG samples, we critically maintained all required conditions like polymerization inhibition, turbidity, light scattering etc. during printing and confirmed that printed SMGs exhibited similar properties like conventionally synthesized SMG. In this contribution, we presented 3D printed smart hydrogels that can morph according to the desired shapes. Utilizing this phenomenon we have made soft robots like soft gripper, smart capsule etc. Both the temperature responsiveness and swelling property of the hydrogels has been utilized as stimuli for shape transformation. Finally, we analyzed the limitation and potential of 3D printing process and discussed a possible approach for application of 4D printed SMGs in soft robotics. Reference: [1] Amano, Y; Hidema, R; Gong, J; Furukawa, H. Chem Lett.,41, 1029-1031 (2012)