( 21) constructed a functionally graded soft robot powered by combustion and used modulus gradient to reduce local deformation in the robot legs. Structures with graded mechanical properties have been fabricated to minimize stress concentration and to realize combined high compliance and high resilience ( 20). For example, mechanical properties and microstructure of the tissue in tendon-to-bone insertion (enthesis) change gradually for enhancing structural durability ( 19). In contrast, functionally graded materials are ubiquitous both in biology and in engineering applications ( 18). In the previous studies of 3D printing LCEs, filaments may follow various paths in one structure, but they often have identical properties, which are mainly determined by printing parameters such as printing temperature and nozzle size ( 10, 12, 14, 17). The strategy developed here will facilitate potential applications of LCEs in different fields. We further demonstrate mitigation of stress concentration near the interface between an actuatable LCE tube and a rigid glass plate through gradient printing. On the basis of the comprehensive processing-structure-property relationship, we propose a simple strategy to print functionally graded LCEs, which greatly increases the design space for creating active morphing structures. Here, we report a facile method to tailor both the actuation behavior and mechanical properties of printed LCE filaments by varying printing parameters. Despite the advancement in printing LCE, it remains challenging to print three-dimensional (3D) LCE structures with graded properties. Recently, direct ink writing technique has been developed to print LCE structures with various geometries and actuation behaviors.
As a promising actuating material, liquid crystal elastomer (LCE) has been intensively explored in building diverse active structures and devices.
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