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In the current survey, some of the publications may have multiple citations. Publications directly related to other aspects of multi-material additive manufacturing, such as the raw materials are premixed or composited before the 3D printing, or porous materials suitable for secondary material infiltration have been excluded from this survey. To limit the scope of our survey, the emphasis has been on the additive manufacturing of parts made of discrete multiple materials. Finally, we discuss the limitations of current technologies and the challenges for future research. Next, we describe the multi-material 3D and 4D printing for different types of materials: polymers, metals, ceramics, and biomaterials. We first consider the main technologies for printing multi-material objects. Here, we review the technologies and applications of multi-material 3D and 4D printing. In response to the growing interest in this area, the present article aims to provide a broader and updated review on 3D and 4D printing of multi-material parts, by providing a comprehensive list of multi-material additive manufacturing methods published in the literature. For example, review articles covered some of the research done on the multi-material printing prior to 2017. Some surveys of multi-material AM already exist in the literature. The number of research pertaining the additive manufacturing of multi-material parts has steadily increased since 2010. Therefore, a thorough understanding of multi-material 3D and 4D printing is required. A wide range of materials such as polymers, metals, ceramics, and biomaterials has been used in various AM methods to obtain multi-material products. Using multi-material 3D and 4D printing, it is feasible to ameliorate the quality of parts by altering composition or type of materials within the layers that is not easy to obtain by conventional manufacturing methods. Current initiatives in the development of AM tools involve development of multi-material 3D and 4D printing. With the emerging of smart materials, attempts to combine them with AM led to 3D parts that are activated by external stimuli and/or environment over time (i.e., 4D (4-dimensional) printing). Due to special characteristics of AM such as facile and customizable manufacturing, this method is being broadly used in many areas such as electronics, aerospace, robotics, and textile. The world's major industrial countries are promoting 3D printing or additive manufacturing (AM) as a technology foundation of future manufacturing.
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