Mechanical architected metamaterials are a subset of structural composites that offer unique opportunities to expand the material properties space. Traditionally, cellular materials for industrial applications have been fabricated using conventional manufacturing processes such as casting, forming, and machining. To streamline processing times, these cellular structures are typically designed with periodic unit cells (i.e., lattices). While these lattices exhibit impressive stiffness-to-weight ratios, their periodic nature restricts architectural design flexibility and hampers advancements in properties such as fracture toughness and impact energy absorption. Our recent work explores the application of additive manufacturing fabrication techniques to produce intricate, heterogeneous, and aperiodic structures without incurring higher manufacturing costs. Through experiments and simulations, we have demonstrated that these heterogeneous cellular materials exhibit superior performance in applications that require high fracture toughness, strength, and energy absorption—for instance, for structural applications and bio-implant design. We will also discuss future research opportunities for these multifunctional materials to be used in a wide range of applications in the aerospace, automotive, sports, and biomedical sectors.