3D Printed Shape Memory Hydrogels for Soft Robotics

Abstract

Hydrogels possess three-dimensional polymeric networks and capable of absorbing large amounts of water or biological fluids. Due to their high water content, porosity and low friction they closely simulate natural living tissue. The properties of a polymer gel depend on the chemical structures of the component molecule and can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are unique materials that have the ability to return from a temporary deformed state to their permanent i.e. original shape induced by an external stimulus like temperature change. Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs [1] show thermoresponsive shape memory behavior when temperature was raised above 40 °C. Although being a hydrogel they are mechanically very strong along with good flexibility and transparency. In this work, we applied stereolithographic (SLA) process to fabricate DMMA-co-SA SMGs using our customized 3D printer named as SWIM-ER. Using SWIM-ER we were able to print sample models like gel sheets and tubes of SMGs that were transparent, flexible and strong. However, printing of SMGs was not an easy task due a number of issues like sample polymerization inhibition, turbidity, swelling during printing and shape deformation. We critically maintained these conditions and resulted SMGs were compared with that of conventionally synthesized SMGs to find out the effect of printing on the mechanical and swelling properties. Finally, we analyzed the limitation and potential of 3D printing process and discussed a possible approach for application of 3D printed SMGs in soft actuators and sensors. Reference: [1] Amano, Y; Hidema, R; Gong, J; Furukawa, H. Chem Lett.,41, 1029-1031 (2012)