【Frontiers in HaiChuan Chemical Technology】Researchers from the University of Science and Technology of China used PLA and TPU materials for 3D printing of biomimetic gradient structural materials that can resist high-speed impacts

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Researchers used PLA and TPU materials to 3D print biomimetic gradient structural materials that can resist high-speed impacts. 2025-06-12 14:48:57 Engineering structural materials used for protection often face complex operating conditions. Existing engineering protective materials mostly adopt design schemes such as laminate structure, unit cell structure, and sandwich structure. Although related materials possess excellent impact resistance, they are still constrained by issues such as interlayer delamination, excessive weight, and the conflict between strength and toughness, which gradually makes it difficult for them to meet the demands of increasingly complex service environments. Biological armor in nature provides a rich source of inspiration for the development of impact-resistant materials. Among them, scales, as the outermost “protective gear” of fish, play a crucial role in protecting the underlying soft tissues, which has attracted extensive attention from researchers. Structurally, the collagen nanofibers in fish scales typically aggregate unidirectionally into thin layers which then stack in a spiral arrangement to form an ordered Bouligand structure; toughness is achieved through mechanisms such as slip, deformation, twisting, and reorientation of these fibrous elements. In addition to this single Bliogan structure, researchers have discovered in the ‘fossil’ coelacanth a unique dual Bliogan structure, which is composed of two sets of single Bliogan structures nested within one another. Through quasi-static mechanical tests, the researchers found that this structure exhibits superior mechanical properties compared to traditional single-Braggian structures (such as those found in the scales of giant bonefish). However, there is still a lack of research on the dynamic mechanical properties of dual Brillouin structure systems, as well as on the protective capabilities of the broader class of Brillouin structure systems under a wide range of loading velocities. It is of great scientific significance and practical value to delve deeply into the wisdom behind biological braggan structures in order to design and develop protective engineering structural materials that can be used in complex environments. Recently, building on previous research on biomimetic Bouguer structure materials, the team led by Academician Yu Shuhong from the University of Science and Technology of China proposed a unique design concept for a gradient dual Bouguer (DT-Bou-G) structure, taking into account both fiber structure design and component regulation. This approach aims to explore the feasibility of developing high-performance protective structural materials that can perform well under a wide range of loading speeds through synergistic toughening mechanisms (Figure 1). The research team used soft thermoplastic polyurethane (TPU) and hard polylactic acid (PLA) as the basic model materials, and through dual-material fused deposition 3D printing technology, achieved a gradual transition of the material composition from hard PLA to soft TPU (a gradient change), thereby creating a new type of biomimetic DT-Bou-G composite material. Compared with the orthogonal structure (UL), single Bouligand structure (BOU), double Bouligand structure (DT-Bou), and double Bouligand alternating structure (DT-Bou-A) materials, this composite material exhibits superior protective performance in quasi-static mechanical tests (unilateral open-circuit beam), low-speed impact tests (pendulum impact and falling weight impact), and high-speed impact tests (bullet impact). The relevant research findings were published in the international journal Science Advances under the title “Gradient double-twisted Bouligand structural design for high impact resistance over a wide range of loading velocities”. The first authors of the paper are Wen Shaomeng, a postdoctoral researcher in the Department of Chemistry, and Gao Weitao, a doctoral student in the Department of Modern Mechanics. The corresponding authors are Chen Siming, an associate researcher at the Hefei Microscale Material Science Research Center, Zheng Zhijun, a professor in the Department of Modern Mechanics, and Academician Yu Shuhong. Studies show that the DT-Bou-G structural material exhibits higher energy absorption at various impact velocities (Figures 2A-C). In low-speed pendulum impact and falling weight impact tests, the DT-Bou-G structure can achieve enhanced toughness through a unique transverse fiber blocking mechanism (Figure 2D). In high-speed bullet impact tests, the fiber structure design fails to provide effective resistance to the loads. At this point, the variation in the gradient composition of the fibers becomes more important; it can effectively reduce impact forces and absorb energy, thereby providing the DT-Bou-G structural material with excellent protective properties (Figures 2E-F). Meanwhile, compared with the alternating structure design (DT-Bou-A), the DT-Bou-G structure with gradient composition characteristics can effectively prevent the delamination phenomenon commonly seen in protective materials (Figure 2G). The research team conducted further finite element simulation studies and found that under low-speed falling weight impact, the DT-Bou-G structure with gradient composition characteristics can dissipate more energy through a wider stress distribution range (Figure 2H) ； Under the impact of high-speed bullets, all the UL, S-Bou, and DT-Bou structures are penetrated, with little difference in the residual impact velocity, whereas the DT-Bou-G structure can effectively deflect the bullet. This indicates that structural design is unable to respond promptly in the face of high-speed impacts, whereas a gradient composition design can provide effective protection. Overall, the dual Bricont structure exhibits a more complex crack propagation path compared to other structures through crack deflection and fiber blocking, whereas the gradient composition design enhances energy absorption by expanding the stress distribution range and enabling greater plastic deformation dissipation. This work demonstrates the synergistic effect of biomimetic structural design and component optimization in impact-resistant materials, achieving simultaneous improvement in the material’s protective performance across all speeds. It provides new design approaches for the development of protective structural materials suitable for use in complex environments in the future. This research was supported by the **Key Research and Development Program, the Strategic Priority Research Programs of the Chinese Academy of Sciences,** key projects of the National Natural Science Foundation, the New Foundation Researcher Program, major basic research projects in Anhui Province, and the Anhui Provincial Outstanding Young Scientists Fund.