Lightweight, ultra-strong three-dimensional microstructured composite carbon micro-dot matrix metamaterial

For a long time, the preparation of lightweight materials with high strength but excellent deformation bearing capacity has been considered a “holy grail” in the study of structural materials, but the mechanical properties of these materials are usually mutually exclusive.

Recently, the latest research by Lu Yang and collaborators of the City University of Hong Kong has found a low-cost, easy-to-operate method to transform common light-cured 3D printed polymer structures into lightweight, highly tough and biologically compatible composite carbon material structures. In addition to traditional structural parts, this method can also be used to easily create lightweight and complex 3D micro-dot matrix superstructures with highly adjustable mechanical properties, showing broad application prospects such as delicate coronary stents and medical stents. On September 1, 2022, the research was published in The Cell Press journal OfFinder, under the title of “Lightweight, ultra-tough, 3D-architected hybrid carbon microlattices.”

The first author of the paper is Dr James Utama Surjadi, a postdoctoral fellow in the Department of Mechanical Engineering at the City University of Hong Kong. The corresponding author is Professor Lu Yang of the Department of Mechanical Engineering, City University of Hong Kong. Collaborators include Professor Jiankai Wang of the Department of Mechanical Engineering at CityU and Professor Raymond H.W.Lam of the Department of Biomedical Engineering and his research team.

In recent years, the research and development of micro-dot matrix metamaterials has been on the rise, combining the advantages of lightweight structural design with the inherent properties of its constituent materials. Due to their complex geometry and fine multi-stage architecture, manufacturing these micro-dot arrays requires precision-based 3D printing technology, but the range of materials available for direct, high-precision 3D printing is still relatively limited, often still based on light-curing resins/polymers. However, compared to metals and ceramics, 3D printed photocuring polymers generally lack excellent mechanical strength or toughness, until recent studies have reported the use of pyrolysis (pyrolysis) methods, these 3D printed polymers can be converted into pure carbon material architecture. However, this process loses almost all of the toughness of the original polymer, resulting in a highly strong, stiff but brittle material, like glass carbon, which limits its wide range of structural material applications.

A team of researchers at city university of Hong Kong has discovered a “magical” pyrolysis condition. By carefully controlling the heating rate, temperature, duration and gas environment, the stiffness, strength and deformability of the 3D printed photocuring polymer micro-dot matrix can be greatly improved in one step, and the polymer can be converted into a super tough three-dimensional structure comparable to the metal alloy, with a strength increase of 100 times and a plasticity of more than doubled. This discovery completely breaks the general perception of pyrolytic materials and will have a profound impact on the development of lightweight, strong and easy-to-use superstructured materials.

The microstructure and super toughness of the “composite carbon” micro-dot matrix material are displayed

In addition to their superior mechanical properties, the team also found that these “composite carbon” microdissectories showed superior biocompatibility compared to the initial state of light-cured polymers: through cytotoxicity and cell behavior monitoring experiments, cells cultured on the composite carbon microplast showed better viability, greater diffusion area, and distance than cells cultured on the polymer microplast. This means that the advantages of partially carbonized composite carbon dot matrix materials may extend beyond mechanical properties and have the potential to be applied to other multifunctional fields.

“We anticipate that this approach may also be applicable to other types of functional polymers, and that the geometric flexibility of these composite pyrolytic carbon metamaterials allows their mechanical properties to be customized for specific structural and functional applications, such as biomedical scaffolds, miniature unmanned aerial vehicles, flexible energy harvesting and storage devices, and so on… This provides a low-cost, simple, and scalable path to easily manufacture lightweight, high-strength mechanical metamaterials of virtually any geometry. Lu Yang said.

The research was supported by the Hong Kong Institute for Advanced Study (HKIAS), the Shenzhen Municipal Science and Technology Innovation Commission and the National Natural Science Foundation of China (NSFC). (Source: Science Network)

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