Meta-biomaterials.

Meta-biomaterials are designer biomaterials with unusual and even unprecedented properties that primarily originate from their geometrical designs at different (usually smaller) length scales. This concept has been primarily used in the context of orthopedic biomaterials with the ultimate aim of improving the bone tissue regeneration performance of implants and decreasing the risk of implant-associated infections. In this paper, we review the ways though which geometrical design at the macro-, micro-, and nanoscales combined with advanced additive manufacturing techniques (3D printing) could be used to create the unusual properties of meta-biomaterials. Due to their intended applications in orthopedics, metallic and hard polymeric biomaterials have received the most attention in the literature. However, the reviewed concepts are, at least in principle, applicable to a wide range of biomaterials including ceramics and soft polymers. At the macroscale, we discuss the concepts of patient-specific implants, deployable meta-implants, and shape-morphing implants. At the microscale, we introduce the concept of multi-physics meta-biomaterials while also covering the applications of auxetic meta-biomaterials for improving the longevity of orthopedic implants. At the nanoscale, the different aspects of the geometrical design of surface nanopatterns that simultaneously stimulate the osteogenic differentiation of stem cells and kill bacteria are presented. The concept of origami-based meta-biomaterials and the applications of self-folding mechanisms in the fabrication of meta-biomaterials are addressed next. We conclude with a discussion on the available evidence regarding the superior performance of meta-biomaterials and suggest some possible avenues for future research.