Abstract
Functional and mechanical properties of novel biomaterials must be carefully evaluated to guarantee long-term biocompatibility and structural integrity of implantable medical devices. Owing to the combination of metallic bonding and amorphous structure, metallic glasses (MGs) exhibit extraordinary properties superior to conventional crystalline metallic alloys, placing them at the frontier of biomaterials research. MGs have potential to improve corrosion resistance, biocompatibility, strength, and longevity of biomedical implants, and hence are promising materials for cardiovascular stent applications. Nevertheless, while functional properties and biocompatibility of MGs have been widely investigated and validated, a solid understanding of their mechanical performance during different stages in stent applications is still scarce. In this review, we provide a brief, yet comprehensive account on the general aspects of MGs regarding their formation, processing, structure, mechanical, and chemical properties. More specifically, we focus on the additive manufacturing (AM) of MGs, their outstanding high strength and resilience, and their fatigue properties. The interconnection between processing, structure and mechanical behaviour of MGs is highlighted. We further review the main categories of cardiovascular stents, the required mechanical properties of each category, and the conventional materials have been using to address these requirements. Then, we bridge between the mechanical requirements of stents, structural properties of MGs, and the corresponding stent design caveats. In particular, we discuss our recent findings on the feasibility of using MGs in self-expandable stents where our results show that a metallic glass based aortic stent can be crimped without mechanical failure. We further justify the safe deployment of this stent in human descending aorta. It is our intent with this review to inspire biodevice developers toward the realization of MG-based stents.
Highlights
Crystalline solid-state materials with all types of chemical bonds, i.e., van der Waals, hydrogen, covalent, ionic, and metallic, can be made amorphous by various techniques [1,2]
The high corrosion resistance and biocompatibility of MGs can be explained by the absence of structural defects, such as grain boundaries, especially on the surface of metallic glasses, as well as their chemical homogeneity, which act as oxidation sites [6,187]
In our recent work [247], we aimed to study the mechanical behaviour of a prototypical Zr-based bulk metallic glasses (BMGs) during crimping of four SX stents designed for percutaneous applications, including percutaneous carotid artery stenting (CAS), transcatheter aortic valve implantation (TAVI), percutaneous cava valve implantation, and transcatheter mitral valve replacement (TMR)
Summary
Crystalline solid-state materials with all types of chemical bonds, i.e., van der Waals, hydrogen, covalent, ionic, and metallic, can be made amorphous by various techniques [1,2]. As we will discuss in detail in this article, due to such a severe localized plastic deformation, application of MGs in balloon-expandable stents is constrained, and certain caveats must be taken into account to design other devices, such as self-expandable stents To clarify these important concepts, here, we first try to provide a brief yet comprehensive review of metallic glasses from the materials science point of view. By systematic investigation of the GFA in ternary systems of Fe and Al metals with rare-earth elements, they obtained exceptional BMGs such as La–Cu–Al samples with thicknesses of several millimetres [30] Based on these findings, quaternary and quinary BMGs, such as La–Al–Cu–Ni and La–Al–Cu–Ni–Coat, were synthesized with low cooling rates of less than 100 K/s. In addition to the continuous search for novel BMG forming alloys, the development of innovative manufacturing techniques is an active and persisting research topic, which is further discussed
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