Robotic conformal 4D printing of liquid crystal elastomers.

Abstract

Four-dimensional (4D) printing of liquid crystal elastomers (LCEs) serves as a promising approach to create reversibly shape-changing structures for diverse applications, including soft robotics, deployable systems, and adaptive surfaces. Central to programming these shape transformations is the spatial alignment of microscale liquid crystal mesogens. Existing 4D printing methods for LCEs are constrained by the alignment of mesogens within 2D planes, thereby limiting the range of achievable deformation. This work presents a robotic direct-ink-writing conformal 4D printing technology that enables deposition of LCEs onto complex, nonplanar 3D substrates. An algorithm is developed to generate printing paths, point normals, and control codes to guide the motion of a six-axis robotic arm. Conformal printing is demonstrated on various surfaces with different printing paths, and the resulting shape-changing behaviors are studied to highlight the unlocked design space. Integration with 3D scanning further allows printing onto substrates with unknown geometries, such as egg surfaces, which enables applications in on-demand protective coatings and structural repair.