Scientific Advances in 2D/3D/4D Additive Manufacturing

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Supra-nano-dual-phase magnesium alloy


Fabricating materials with complex shapes and desirable properties for various applications has long been a focus of materials scientists and engineers. A leading expert at CityU, who developed the world’s first supra-nano-dual-phase alloy and four-dimensional (4D) ceramic printing, is working on integrating these two cutting-edge technologies to fabricate lightweight, high-strength metallic materials for biomedical and aerospace applications.

3D printing technology, also known as additive manufacturing, has been widely used to fabricate components with complex shapes at low cost in the manufacturing, construction, biomedical and aerospace industries. However, some applications still face limitations. For example, the 3D-printed metallic materials commonly used as moving parts in medical implants have insufficient fatigue and wear resistance, which may eventually lead to the need for a second surgery to replace the implants. 

Integrating two cutting-edge technologies

Professor Lu Jian, Chair Professor of Mechanical Engineering at CityU, and Director of the Hong Kong Branch of National Precious Metals Material Engineering Research Center and the Centre for Advanced Structural Materials, is an expert in the mechanical properties of metallic and ceramic materials. He is leading a team to develop a pioneering 2D/3D/4D additive manufacturing system to fabricate metallic-based materials with desired mechanical properties for different applications. 

“It is worthwhile integrating our two technologies – dual-phase nanostructuring and 4D printing – to explore any extraordinary mechanical properties or metamaterial properties that may emerge,” said Professor Lu, who is also the Director of the Joint Laboratory of Nanomaterials and Nanomechanics, established by the Institute of Metal Research (IMR) of the Chinese Academy of Sciences and CityU. 

Earlier, he led the team that successfully developed the first-ever supra-nano-dual-phase magnesium alloy. By using dual-phase nanostructuring technology, the team overcame the limitation of existing structural materials: high strength and high ductility cannot coexist. The new cutting-edge material developed by the team is 10 times stronger than conventional crystalline magnesium alloy and has super-deformation capacity two times higher than that of magnesium-based metallic glass. The findings were reported in the prestigious scientific journal Nature

They also invented the world-first 4D printing of ceramics. The 3D-printed ceramic precursors can re-shape by themselves over time with the elastic energy stored in the stretched precursors. And the fabricated ceramics are mechanically robust with high specific strength.

The 3D-printed ceramic precursors are soft and stretchable, enabling ceramics with complex shapes, such as origami folding mimicking the Sydney Opera House.


Fabricating ideal implant materials

In this project, they will first develop a 2D/3D/4D manufacturing system to fabricate metallic-based materials with complex shapes, particularly those used in biomedical and lightweight structure applications. Since titanium-based alloys are considered the ideal implant material for clinical use, the team will first focus on fabricating supra-nano 3D-printed titanium-based alloy and examine its mechanical properties.

“By applying our knowledge and know-how gained in inventing the 4D printing technique, fabricating supra-nano materials, and producing surface nanostructured materials, we will further treat the 3D-printed titanium-based alloy and other metallic materials to enhance their mechanical properties. We hope to develop lightweight metallic materials with high strength and wear resistance for the medical implant and aerospace industries,” said Professor Lu.  

Professor Lu Jian (left), Dr Liu Guo and the research team have developed the world's first-ever 4D printing for ceramics.


In particular, they will study the effect of post-treatment, such as Surface Mechanical Attrition Treatment (SMAT) to enhance fatigue resistance, and Physical Vapour Deposition to enhance wear resistance, on the mechanical properties of the printed materials. SMAT is a surface nano-crystallisation technology, which was first introduced by Professor Lu and Professor Lu Ke, Director of IMR. It involves the use of hundreds of small hard balls, which are vibrated using high-power ultrasound, so that they hit the surface of a material at high speed to enhance damage-tolerance in metallic alloys. 

Biosensors for health
They aim to build up a database of 3D-printed metallic materials, with details about their mechanical properties, microstructure, treatment process and potential applications. “The database will be of great assistance to materials researchers and engineers for their research in developing more new materials and for exploring new applications,” said Professor Lu. “We hope it can help facilitate the application of metallic materials in different fields, thus benefiting all of society.”  

The SERS biosensing technology can be used to test contaminants in food and cosmetics. 


Besides 3D printing technology, Professor Lu and his team have worked on functional metallic materials, particularly their newly developed biosensing technology based on ultrasensitive surface enhanced Raman spectroscopy (SERS). This technology can be applied in various areas, such as antibiotics detection, and food and cosmetics product safety. They are working on the feasibility of applying it in the fast detection of Covid-19, cancer and cardiovascular diseases, as well as the non-invasive detection of diabetes. 

This research article originated from CityU RESEARCH.

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