Three-dimensional printing of complex structures: man made or toward nature?

Current three-dimensional (3D) printing techniques enable the fabrication of complex multifunctional structures that are unimaginable in conventional manufacturing. In this Perspective, we outline recent progress in materials and manufacturing and propose challenges and opportunities for the future development of 3D printing of functional materials. The success of future 3D printing relies not only on multifunctional materials and printing techniques but also on smart design of complex systems. Engineers need to understand advanced materials, additive manufacturing, and, more importantly, creative design. Fortunately, we can learn from many structures that exist in nature and adapt them to engineered structures.