Nature does nothing in vain. Through millions of years of revolution, living organisms have evolved hierarchical and anisotropic structures to maximize their survival in complex and dynamic environments. Many of these structures are intrinsically heterogeneous and often with functional gradient distributions. Understanding the convergent and divergent gradient designs in the natural material systems may lead to a new paradigm shift in the development of next-generation high-performance bio-/nano-materials and devices that are critically needed in energy, environmental remediation, and biomedical fields. Herein, we review the basic design principles and highlight some of the prominent examples of gradient biological materials/structures discovered over the past few decades. Interestingly, despite the anisotropic features in one direction (i.e., in terms of gradient compositions and properties), these natural structures retain certain levels of symmetry, including point symmetry, axial symmetry, mirror symmetry, and 3D symmetry. We further demonstrate the state-of-the-art fabrication techniques and procedures in making the biomimetic counterparts. Some prototypes showcase optimized properties surpassing those seen in the biological model systems. Finally, we summarize the latest applications of these synthetic functional gradient materials and structures in robotics, biomedical, energy, and environmental fields, along with their future perspectives. This review may stimulate scientists, engineers, and inventors to explore this emerging and disruptive research methodology and endeavors.

大自然不会做任何徒劳的事。经过数百万年的革命，生物体已经进化出分层和各向异性的结构，以最大限度地在复杂和动态的环境中生存。许多这些结构本质上是异质的，并且通常具有功能梯度分布。了解天然材料系统中的收敛和发散梯度设计可能会导致能源、环境修复和生物医学领域急需的下一代高性能生物/纳米材料和设备的开发发生新的范式转变。在此，我们回顾了基本设计原理，并重点介绍了过去几十年发现的梯度生物材料/结构的一些突出例子。有趣的是，尽管在一个方向上具有各向异性特征（即，在梯度组成和性质方面），这些自然结构保留了一定程度的对称性，包括点对称、轴对称、镜像对称和3D对称。我们进一步展示了制作仿生对应物的最先进的制造技术和程序。一些原型展示了超越生物模型系统的优化特性。最后，我们总结了这些合成功能梯度材料和结构在机器人、生物医学、能源和环境领域的最新应用及其未来前景。这篇评论可能会刺激科学家、工程师和发明家探索这种新兴的、颠覆性的研究方法和努力。