Liquid crystal elastomers by photopolymerization: from chemistry and alignment strategies to 4D printing.

Liquid crystal elastomers (LCEs) are materials that combine the anisotropy of liquid crystal molecules with the elasticity of lightly crosslinked polymer networks, making them promising for soft actuators. Photopolymerization has emerged as a key route for the design and implementation of LCEs, thanks to its broad chemical versatility and its compatibility with additive manufacturing, a field that had developed rapidly in recent years. However, this approach has not yet been comprehensively addressed, despite its central role in enabling LCE-based actuators and 4D-printed devices. This review aims to provide a comparative framework showing how chemical design governs material properties and defines compatible alignment strategies. Furthermore, it examines how the coupling between chemical structure and alignment can be integrated within additive manufacturing processes. By linking photopolymerization mechanisms, alignment strategies, and 4D printing processes, this review establishes guidelines for selecting suitable light-based chemistries, and for designing LCE networks with tailored properties.