Additive manufacturing of stiffness optimised auxetic bone scaffold using cobalt-chromium-molybdenum superalloy

Abstract

Auxetic materials offer unconventional strain behaviour owing to their negative Poisson’s ratio (−𝜐) leading to deformation modes and mechanical characteristics different to traditional porous architecture. This can lead to favourable outcomes for load-bearing tissue engineering constructs, such as bone scaffolds for critical-size defects. Emerging early-stage studies have shown the potential of auxetic architecture in increasing cell proliferation and tissue reintegration due to their −𝜐. However, research on the development of stiffness optimised auxetic architecture for biomedical applications including bone scaffolds or implants is yet to be reported. In this regard, the thesis puts forward an open innovation framework for the selective laser melting (SLM) of auxetic bone scaffolds that offer the strength and porosity requirements while offering stiffness matching to a tibia host section. CoCrMo has been chosen as the biomaterial of choice due to its high elastic modulus and density which offered the potential for conceiving highly porous architectures. CoCrMo stiffness matched auxetic bone scaffolds optimised under two scenarios for their potential to offer near-zero and high negative Poisson’s ratio are demonstrated in this thesis. Overall, the investigations carried out in this thesis suggest that CoCrMo auxetic bone scaffolds can be additively manufactured with targeted Poisson’s ratio, mechanical performance and porosity characteristics by algorithmically modifying the design parameters. The surrogate model developed in this thesis can be used for user-defined scenarios to generate scaffolds with near-zero and high −𝜐, respectively while offering stiffness matching to host bone. Manufacturers and research institutions can use the validated methodology proposed in this thesis to further refine and generate alternate prototypes to inform further developments in the field of meta-biomaterials.