3D Printing in alloy design to improve biocompatibility in metallic implants

Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.

Detailed descriptions of the structural features of bone abound in the literature; however, the mechanical properties of bone, in particular those at the micro- and nano-structural level, remain poorly understood. This paper surveys the mechanical data that are available, with an emphasis on the relationship between the complex hierarchical structure of bone and its mechanical properties. Attempts to predict the mechanical properties of bone by applying composite rule of mixtures formulae have been only moderately successful, making it clear that an accurate model should include the molecular interactions or physical mechanisms involved in transfer of load across the bone material subunits. Models of this sort cannot be constructed before more information is available about the interactions between the various organic and inorganic components. Therefore, further investigations of mechanical properties at the 'materials level', in addition to the studies at the 'structural level' are needed to fill the gap in our present knowledge and to achieve a complete understanding of the mechanical properties of bone.