Graded biological materials and additive manufacturing technologies for producing bioinspired graded materials: An overview

Functionally graded materials (FGMs) are desirable in a variety of applications. Due to a lack of understanding of design and manufacturing methods, it remains a challenge to engineer FGMs. Gradient patterns and performance shown in biological materials present motifs for designing FGMs. The bottom-up characteristic of additive manufacturing (AM) enables unparalleled control over material and structure, making AM a perfect candidate for FGMs. The integration of the two provides an unprecedented opportunity for developing next generation advanced materials. In this review, we firstly detail the biological gradient materials/structures in terms of their functions. Subsequently, the art-of-the-state AM methods for fabricating FGMs are reviewed, with a focus on the technology types of AM that can prepare biomimetic material and structural FGMs, especially emphasizing the multiform gradients induced by processing parameters. Then, the performance and application cases of FGMs created by AM are summarized. Finally, an outlook for further developments of AM technologies towards FGMs is provided.