4D Printing: Technologies, Materials and Applications

Since the 1980s, the idea of 3D printing has set off a research upsurge. Due to its advantages of material efficiency, excellent surface resolution and high efficiency in one-step production, 3D printing has been widely used in biomedical, electronics, self-healing technology, engineering applications and bionics fields. However, 3D printing technology also has some shortages, it cannot control the addition technology to produce complex structure or suppress the size change and anisotropy behavior of strain control. In order to overcome the complexity and inflexibility of printing size, people introduced the concept of 4D printing. 4D printing is an interdisciplinary research based on intelligent materials, 3D printers and design. Compared with the static structure produced by 3D printing, 4D printing contains a dynamic structure which means 4D allows 3D printed structures to respond to external stimuli (such as temperature, light, water, etc.) and change their shape or function over time, so that the printed product is no longer limited to a fixed shape, but presents a variety of changes. 4D printing attracts a lot of interest since it was first conceptualized in 2013. The fourth dimension gives vitality to design, which uses stimuli to drive the transformation of smart materials by shape memory effects. Intelligent materials are sensitive to the environment which including polymers, alloys, hydrogel, ceramics, composite materials and so on. Through the environment stimuli like thermal pre-strain, water absorption, electromagnetic radiation, activation, magnetic field, current, voltage, the solvent and pH, smart materials will self-assembly produce a deformation, decomposition, repair even change the properties or functions, showing a variety of morphological characteristics. 4D printing has been widely tried in drug delivery, wearable electronics, fashion, automatic origami structures, sensors and other engineering applications by mimicking natural processes (flowers bloom, plant changes and sunflower movements) and exploring similar characteristics of materials. This review focuses on the system and specific application of 4D printing materials and list a brief overview of the 4D printing about its history, definition, principle and basic composition. We look back the latest development of 4D printing materials and state both the development and challenges of related application fields like the biological bionic, biological, medical, the progress of the application of paper folding structure, etc. Finally, we introduce the trend of 4D printing and the development prospect of the new field to provide reference for further research. © 2021, Materials Review Magazine. All right reserved.