Biomedical titanium-tantalum alloys for orthopedic implant applications: From manufacturing to biological performance

An ideal biomedical material for orthopedic implant applications is characterized by being biologically compatible with the human body, mechanically matching human cortical or cancellous bones, and releasing no cytotoxic ions over its servicing time. Titanium-tantalum (Ti-Ta) binary alloy is such a potential biomaterial that is composed of the most biocompatible metal elements, and both metals have been heavily used as implant materials in clinical surgeries for decades. Additive manufacturing (AM) enables the innovative design of patient-specific medical implants, e.g., Ti-Ta lattices which display unique mechanical and biological properties. Such Ti-Ta lattice implants can best mimic the mechanical properties of natural bones and offer open pores and pore networks to promote implant-bone biological interactions, which are essential to successful and long-term implantation. This article extensively reviews the biomedical Ti-Ta alloys. It starts with a brief overview of Ti-Ta alloy development, then elaborates on its manufacturing, the resulting microstructures pertinent to cooling conditions, mechanical properties, and surface modification to improve the bioactivity. Ti-Ta lattices from AM process are particularly highlighted as they enable elastic moduli close to those of natural bones. Next, the corrosion resistance and wettability of Ti-Ta alloys are addressed. Last, the biological responses of Ti-Ta alloy in vitro and in vivo are scrutinized and discussed, highlighting the significance of the biocompatible Ti-Ta chemistry, the surface features and the AM-enabled lattice structures. This paper aims to establish a comprehensive and systematic understanding of binary Ti-Ta alloys for biomaterials research and artificial bone implant applications.