Free-Form Printing and Deformation Control Strategies for Liquid Crystal Elastomers

Fabrication pathways for liquid crystal elastomer (LCE) have remained a topic of intensive research interest in recent years. Photopatterning and two-stage reaction techniques were pioneering methods which enabled molecular patterning and fabrication of LCE networks in few, relatively simple steps. Recently, additive manufacturing (AM), or 3D printing, has become another promising approach for facile production of LCE networks. The combination of 3D printing with responsive materials, such as LCE, has led to a new generation of smart structures that not only possess a static shape but also can change their shape over time. This process is termed 4D printing, with the fourth dimension being time. The focus of this talk will be on the development of new 4D printing techniques to generate a new class of complex, multi-planar LCE geometries. One of the most notable 4D printing methods, direct ink write (DIW), enables simple fabrication of complex LCE structures by coupling the printing process with the LCE alignment step. This occurs due to the shear forces generated during extrusion through the DIW nozzle. By combining this approach with multiple materials, novel shape transformations can be achieved. For example, by combining LCE with the unique properties of another smart material called shape memory polymers (SMP), the shape transformation can be locked in place. Furthermore, LCE/SMP composites offer superior mechanical properties in both the deformed and undeformed state for functional engineering applications. The structures produced using this method, however, can only perform 2D to 3D shape transformations. Many smart structures applications require more complex 3D shapes to be fabricated. For this reason, we will discuss a recently developed printing method called embedded 4D printing. Here, LCE is extruded into a gel matrix to create complex 3D architectures which can generate unique 3D to 3D shape transformations. This approach enables LCE molecular programming in any 3D cardinal direction. The ability to 4D print complex 3D LCE structures without the need for supports opens new avenues for the design and development of functional and responsive systems such as soft robotics, biomedical devices, and advanced materials engineering.