## 1 Introduction  
The term additive manufacturing (AM) was coined in the 1990s to describe a new technology capable of manufacturing 3D components through a layer-by-layer deposition. According to ISO/ASTM 52900:2017 [1], AM is \"the process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive and formative manufacturing technologies\". Material extrusion (ME) is one of the most widely used AM technologies owing to its simplicity and low cost. This technique forces the extrusion material through a nozzle, which follows a predetermined path to build the component onto a build platform, layer upon layer. In the ME process, extruded materials are generally thermoplastic filaments with poor mechanical properties [2; 3; 4; 5; 6]. In general, parts manufactured using ME technology are excellent for prototyping and visualization purposes; however, they are rarely used for load-bearing applications owing to their lack of strength. This technical issue has limited the use of ME in mechanical applications. Extensive research is underway to improve the mechanical properties of ME components and thereby extend the applications of this technology. Fiber-reinforced polymers have been investigated for decades owing to their tailored material properties and high specific strength. Fiberglass and carbon are the most widely used fibers in combination with a polymer matrix. The polymers hold and protect the fibers and transfer the load to the reinforcement, while fibers support the load by providing excellent resistance to the structure. A clear improvement in the ultimate tensile strength (UTS) of polymeric samples reinforced with fiberglass and carbon fibers is presented in [7, 8]. Particular attention is also given to the use of filaments containing metal powders, which allow the manufacturing of metal parts with improved properties compared with those of polymer composites. A few studies have been conducted on the reinforcement of polymeric filaments with metallic particles. [PERSON] et al. [9] stated that the tensile strength of specimens decreased with an increase in the copper and iron contents in the thermoplastic filaments. Likewise, [PERSON] et al. [10] confirmed the deterioration of the mechanical properties of samples with the addition of type 420 stainless steel particles. In [11], an increase in the volume fraction of iron particles reduced the fracture energy. Furthermore, the authors indicated that the variations in the tensile strength and tensile elongation were strongly dependent on the size of the metal particles. Thus, a smaller particle size of the composite generated a larger tensile elongation at break but with a degradation in the tensile strength. Polymer-metal composites reduce the mechanical performance owing to the difficulty in achieving uniform particle distribution and strong adhesion between the metal powders and polymer matrix. Poor adhesion generates large voids at the interfaces between the particles and matrix, which induce cracks upon loading. The bending behavior of parts printed with the metal-polymer blends was not adversely affected by the separation of the filler from the polymer matrix during the test. [PERSON] et al. [12] performed flexural strength tests on polyethylene-copper samples, demonstrating that the addition of metal particles increased the maximum flexural strength up to 19.41 MPa. [PERSON] et al. [13] enhanced the mechanical properties of specimens by interlacing copper mesh layers within a polymer matrix during the tests. The tensile strength, flexural strength, and Rockwell hardness slightly improved in comparison to those of the polymeric samples. Similarly, [PERSON] et al. [14] pointed out that the mechanical properties of objects printed with metal-polymer blends were compared to common PLA-printed objects. Shaping, debinding, and sintering [15] is a promising multi-step ME process that overcomes the limitations associated with the poor mechanical properties of highly filled polymeric filaments.