The advancements in additive manufacturing (AM) technology make the fabrication of complex architected materials and structures at multiple length scales possible to explore a new family of metamaterial. A metamaterial is an artificially engineered material to have a property not found in conventional materials. [1] Historically, the term "metamaterials" were limited to electromagnetism field, but, recently, it has been extended to photonic, phononic, and mechanical systems to design architected engineered materials that exhibit properties not usually found in conventional materials. [2] Mechanical metamaterials refer to a sort of metamaterials that designed artificial structural materials with counterintuitive mechanical properties derived from their tailored internal microstructure rather than the composition of base material. [3] The unusual properties include negative Poisson's ratio, negative modulus of elasticity, and negative compressibility. [4,5] Examples of mechanical metamaterials include acoustic metamaterials, auxetic materials, pentamode metamaterials, and micropolar metamaterials. The concept of metamaterials combined with AM opens new design avenues for the fabrication of complex microstructures over a wide range of length scales. [6][7][8] Auxetic mechanical metamaterials are recognized by a negative Poisson's ratio; i.e., materials will contract (expand) in the transverse direction when compressed uniaxially (stretched). Auxetic mechanical metamaterials are of interest because of their enhanced mechanical properties, such as increased indentation resistance, [9] shear modulus, [10] and fracture toughness. [11] They have a great potential in engineering applications, such as cellular materials with superior damping and acoustic properties, [12] piezoelectric metamaterials, [13] piezocomposites, [14] auxetic fasteners, [15] bioprostheses, [16] tissue engineering, [17] and mechanically tunable, elastically reversible, and transformable topological mechanical metamaterials. [18,19] The negative Poisson's ratio of auxetic material depends on the topology of auxetic building blocks and scaleindependent. [20,21] Several natural materials exhibit negative Poisson's ratio, such as silicates, [22] cubic elemental metals, [23] zeolites, [24] natural layered ceramics, [25] and monolithic ferroelectric polycrystalline ceramics. [26] Love [27] was the first to report the negative Poisson's ratio of naturally occurring cubic crystals of