Development of Liquid Crystalline Networks as photo-responsive actuators for microrobotics

Active materials, and in particular light-responsive materials, have been explored and used for soft robotics and microrobotics in the last ten years. Among them, liquid crystal networks are promising, presenting a very good response on the millimetre and micrometre scales when exposed to light stimuli. Moreover, they are compatible with many printing strategies, which makes them versatile. This work employs liquid crystal networks based on mono- and bi-acrylate mesogens, combined with monoacrylate azobenzene dyes. The light-actuated networks can be freely 3D patterned and deform depending on the alignment of the network fixed by the polymerization. Two printing strategies are explored. First, stereolithography printing is tested as a millimetric to centimetric approach. This technique is not widely used for liquid crystal printing, as many challenges such as the alignment of the molecules, the stability of the mixture, and the resolution are difficult to master. However, tunable and predictable light-based deformation was achieved with various geometries of centimetric and millimetric shapes using this technique. Limitations in terms of multilayer printing still need to be tackled. Finally, direct laser writing with two-photon polymerization was used for precise micropatterning of micro-actuators based on comparable material. Multimaterial, simple photo-actuated structures were obtained at the microscale and characterized with green laser actuation. However, the in vivo or in vitro use of microrobotics is limited when using light actuation due to potential cell damage from laser illumination, even at 530 nm, because of the high power density. To address this issue, a micrometric gripper integrated directly onto an optical fiber is developed. A fast response and tunable deformation is obtained with an active opening. Additionally, the optical fiber confines the high power density area, which suggests a lower risk of cell damage.