4D Printable Formulations of Mixed Low and High Molecular Weight Liquid Crystalline Units: A Versatile Route to Functional Soft Actuators.

Over the last few years, 4D printing of liquid crystal elastomers (LCEs) has been explored to develop actuators with significant, reversible, and anisotropic shape changes upon external stimuli such as heat or light. Most reported ink formulations rely on photo-curable liquid crystal materials derived from high molecular weight (MW) main-chain macromers. Their rheological properties allow to program molecular alignment during direct ink writing. In contrast, formulations composed mainly of monoacrylate or diacrylate low MW mesogens are unsuitable for extrusion-based 4D printing as they fail to promote mesogen alignment during printing. This shortcoming restricts the range of chemical and physical compositions accessible to 4D printing. Here, we introduce a practical route for formulating 4D printable inks that integrate low MW mesogens. By adding an acrylate-ended macromer to the low MW constituents, these mixtures become suitable for direct ink writing. This enables the preparation of multi-functional actuators with digitally controlled director morphology and tailored properties, for example, stiffness and actuation strain, as well as light-responsive behavior when photoactive molecules are used. These results highlight the versatility of the method and suggest its potential compatibility with other functional low MW units, such as those responsive to electrical or pH stimuli.