3-D printing hierarchical liquid-crystal-polymer structures
Biological materials from bone to spider-silk and wood are lightweight fibre composites arranged in a complex hierarchical structure, formed by directed self-assembly to demonstrate outstanding mechanical properties. When such bioinspired stiff and lightweight materials are typically developed for applications in aircraft, automobiles and biomedical implants, their manufacture requires energy and labor-intensive fabrication processes. The manufactured materials also exhibit brittle fracture characteristics with difficulty to shape and recycle, in stark contrast to the mechanical properties of nature. Existing polymer-based lightweight structure fabrication is limited to 3-D printing, with poor mechanical strength and orientation, while highly oriented stiff polymers are restricted to construct simple geometries. In an effort to combine the freedom of structural shaping with molecular orientation, 3-D printing of liquid-crystal polymers was recently exploited. Although desirable shape-morphing effects were attained, the Young's modulus of the soft elastomers were lower than high-performance liquid-crystal synthetic fibers due to their molecular structure.