Currently, 4D printing can create many objects that 3D printing cannot, and the color, volume, and shape of these objects can change with environmental conditions and stimuli, such as water and temperature. Therefore, microstructures can be deformed according to the pre-designed track under specific time and activation conditions. 3D printing is “pre-modeling + printing of the finished product”, while the idea of 4D printing is to embed the design of the product into a flexible smart material based on 3D printing. With the continuous development of research and technology, the definition of 4D printing will be more comprehensive. defined 4D printing as the AM process that integrates smart materials into the initial form of printed materials for 3D printed structures/components. It is a purposeful evolution of 3D printing structure in shape, structure, and function, intended to effectively realize self-assembly, deformation, and self-repair. 4D printing was originally defined with the formula of “4D printing = 3D printing + time”, which refers to changes in the shape, structure, or function of 3D printing over time. In a TED talk in 2013, he defined 4D printing as a new design of a complex spontaneous structure that changes with time due to the interaction of environment, marking the emergence of the concept of 4D printing. In 2013, professor Tibbits first proposed the concept of 4D printing. This has given rise to a new term, i.e., “4D printing”.

In the industry, 3D printing technology is mainly used for sample manufacturing in the early stage of the development of new products, especially those with a complex structure.ģD microstructures made of smart materials, relying on the functions of these materials, can evolve over time in a predetermined manner. On account of some of the shortcomings mentioned above, 3D printing still cannot completely replace traditional manufacturing. On the other hand, while 3D printing has made great breakthroughs in all aspects, its limitation lies in the layer-by-layer printing speed. However, he microstructures fabricated using 3D printing is static. 3D printing has been widely used in biomedicine, polymer science, space science, and other fields by virtue of its rapid prototyping of 3D products with complex shapes. Currently, additive manufacturing for four-dimensional (4D) printing is mainly divided into two categories: Extrusion-based methods, and vat photopolymerization methods. Since the late 1980s, additive manufacturing (AM), often referred to as 3D printing or rapid prototyping, has been gradually popularized. In 1986, Chuck Hull proposed that three-dimensional (3D) systems applied for a technology of stereolithography (SLA), which attracted the world’s attention and to some extent represented the origin of a 3D printing technology.

In addition, the current challenges and future prospects of 4D printing were highlighted. Herein, recent major progresses in 4D printing are reviewed, including AM technologies for 4D printing, stimulation method, materials and applications. Although 4D printing is mainly based on 3D printing and become an branch of additive manufacturing, the fabricated objects are no longer static and can be transformed into complex structures by changing the size, shape, property and functionality under external stimuli, which makes 3D printing alive. 4D printing originates in 3D printing, but beyond 3D printing. To overcome this challenge, four-dimensional (4D) printing which defined as fabricating a complex spontaneous structure that changes with time respond in an intended manner to external stimuli. However, the microstructures fabricated using 3D printing is static. Since the late 1980s, additive manufacturing (AM), commonly known as three-dimensional (3D) printing, has been gradually popularized.

4d printing technology