Discontinuous Metric Programming in Liquid Crystalline Elastomers

Thermally responsive spatially programmable soft actuators with multiple response states enabled by Grayscale UV light processing

Soft actuators hold great promise for applications in biomimetic robots, artificial muscles, and drug delivery systems due to their adaptability in diverse environments. A critical aspect of designing thermally responsive soft actuators is to achieve spatially programmable actuation under a global thermal stimulus. Different local actuation behaviors can be encoded in one actuator to enable complex morphing structures for different tasks. However, it is challenging to achieve programmability beyond one or binary states. This work introduces a new grayscale ultraviolet (UV) light processing method to fabricate soft actuators with spatially tunable Young's modulus, enabling multiple programmable states in one actuator. Together with a liquid crystal elastomer actuation layer and a photothermal heating layer, the LCE programming layer with spatially programmable moduli allows different regions of the soft actuator to bend to controllable extents under a global thermal stimulus. Various shape morphing patterns can be encoded using UV photomasks with spatially controlled grayscales. Additionally, caterpillar-inspired robots capable of bi-directional crawling and octopus-arm-inspired structures for object manipulation are demonstrated. This work represents advancements in the programmability of thermally responsive soft actuators, laying the foundation for their applications in advanced soft robotic systems.

Shape programming of liquid crystal elastomers

Liquid crystal elastomers (LCEs) are shape-morphing materials that demonstrate reversible actuation when exposed to external stimuli, such as light or heat. The actuation's complexity depends heavily on the instilled liquid crystal alignment, programmed into the material using various shape-programming processes. As an unavoidable part of LCE synthesis, these also introduce geometrical and output restrictions that dictate the final applicability. Considering LCE's future implementation in real-life applications, it is reasonable to explore these limiting factors. This review offers a brief overview of current shape-programming methods in relation to the challenges of employing LCEs as soft, shape-memory components in future devices.