###### Abstract
The advantages of additive manufacturing were engaged in the simulation-driven design methodology to allow for the identification of unit cell geometrical features with increased auxetic responses. Following this process, auxetic prototype systems were fabricated by means of 3D printing with different polymer material combinations. Then, their auxetic behavior was investigated experimentally by means of compression tests and computationally with the aid of finite element analysis. With the use of such proposed auxetic systems, the mechanical requirements of any sandwich composite structure can be adapted for specific impact and protective applications, primarily for structural protection as well as for personal and sport protective equipment for the head, body, and feet. A number of auxetic structure geometries were identified through a literature review. Figure 1 provides a comprehensive overview of existing auxetic structures classified into six major categories: chiral (a), re-entrant (b), perforation (c), origami (d) rotating rigid (e), and others (f). For manufacturing purposes, the internal structure of an auxetic material and its deformation mechanism to \"design\" the macrostructure by tailoring the mechanical properties must be considered [15]. The most common structures of cellular auxetics, in which the deformation mechanism response drives the negative Poisson's ratio, are designated into re-entrant, chiral, and rotating polygon units, although there may be certain re-entrant structural configurations that do not exhibit auxetic behavior [16]. Regardless of the differences between structures, Poisson's ratio is dominated by changes in the internal areas. All of the structures expand under tension (internal areas expand), and while under a compressive load, their internal areas tend to enclose. These microstructural effects are responsible for the macroscopically observed negative Poisson's ratio response. The first re-entrant cellular structure was proposed by [PERSON] and [PERSON] in the form of honeycombs [17]. Re-entrants have been used widely to study the controlled mechanisms of the auxetic effect. A variety of re-entrant structures can be found in 3D or in 2D and are formed by hexagonal, star shape, or arrowhead face cells. When these structures are subject to the uniaxial tensile load, the cell ribs tend to increase (moving outward), resulting in the auxetic effect. [PERSON] [18] and [PERSON] [19; 20; 21] proved that a non-centrosymmetric, chiral structure can produce a negative Poisson's ratio response. The unit cell of this structure can be defined from a central node with six tangentially attached ribs/ligaments. When the uniaxial load is applied, the nodes rotate accompanied by flexure of the ligaments, which rises the auxetic response in the transverse direction. With chiral structures, a Poisson's ratio close to \(-1\) can be obtained. [PERSON] and [PERSON] [22] presented a new structure that can achieve auxetic response by involving the rotation of rigid squares joined with hinges at their vertices. Many authors extended the square geometry of this rotating mechanism to other polygon geometries to capture auxeticity: rotating tetrahedral [23], triangles [24; 25; 26], rectangles [27], and rhombi [28]. Likewise, studies have shown that this is the dominant mechanism of the auxetic response of natural materials, such as zeolite and a-cristobalite [29; 30]. In addition to, and apart from the above mechanisms, auxetic properties can result from a variety of cooperative phenomena, scaling from micro [31] to macro levels [32]. Overall, there are a variety of other auxetic structures found in the literate that show a vast number of possibilities, through varying patterns and configurations, for achieving the desired auxeticity. The geometrical complexity of auxetic structures makes additive manufacturing technologies unavoidable for their creation. Harnessing additive manufacturing to produce auxetic structures is a natural choice due to their intrinsic geometrical complexity.