Bi-Material 3D Printed Soft Microrobots: Proof-of-Concept and Demonstration

This paper proposes to investigate a bi-material approach that introduces another material in the 3D printed soft microrobot working as a structural skeleton of the active material. For the latter, pNIPAM-based hydrogels are good candidates thanks to their large deformation under stimuli. However, this same property is a trade-off with mechanical strength, and by extension the structural stability of the printed microrobots. By combining two materials, the shortcomings of one can be palliated by the second material. Here, we propose to make 3D 100µm-scale tethered microrobots with pNIPAM beams as an actuator into IP-S flexible mechanisms, using bi-material 2-Photon Polymerization (2PP) printing as a fabrication process. The capacity of the pNIPAM beams as actuators is studied experimentally and via Finite Element Modelling, revealing promising capacities in displacement and forces during simulations (contraction up to 25%, force up to
$166\ \mu \mathrm{N}$
). The behavior of pNIPAM-actuated IP-S flexible mechanisms is explored in a 2PP-printed microrobot, demonstrating a state-of-the-art motion range (joint rotation up to
$14^{\circ}$
) easily controllable by temperature change. Furthermore, actuated 3D mechanisms are demonstrated with three 100µm 3D grippers.