**2.5 Sintering-based 3D printing**

3D printing is a new technology, which appeared since the 1980s, used to produce bulk materials (metals, ceramics, composites, etc.) with complex geometry. This technique is based on extrusion followed by sintering. Thus, the advantages of this method are the low cost and the versatile printing strategy. 3D printing allows to fabricate parts in a discrete layer by layer or line by line or point by point from 3D computer-aided design (CAD) models. It is the unique technique that enables to fabricate precise and highly complex parts that are difficult to obtain using traditional techniques [29]. Three-dimensional printing technology is expected to solve the limitations that are inevitably encountered when using traditional methods. 3D printing, also known as additive manufacturing, is based on the principle of layered manufacturing, in which materials are overlapped layer by layer [30]. This technology can be used to quickly fabricate components with any complex shape by accurately accumulating material using solid modeling according to a CAD model or computed tomography (CT) scan under computer control [31]. The 3D printing industry has recently exploded due to the reduced manufacturing costs of 3D printers and to their improved printing precision and speed, allowing for huge advances in medical equipment, implant material, and cell printing.
