Transcatheter cardiovascular devices require high-purity Nitinol materials with exceptional fatigue resistance to meet stringent Class III regulatory durability requirements. Ultra-clean VAR/EBR (Vacuum Arc Remelt/Electron Beam Remelt) Nitinol represents a metallurgical advancement that achieves unprecedented control over inclusion size and distribution. This study characterizes the fatigue behavior of VAR/EBR Nitinol with nominal inclusion sizes below 10 μm under conditions representative of transcatheter mitral valve replacement (TMVR) applications, using the HighLife Mitral Valve Replacement system as a clinical case study. Diamond-shaped fatigue specimens were manufactured from ultra-clean VAR/EBR Nitinol tubing used in the HighLife Mitral Valve Replacement system and tested under physiologically relevant conditions to 107, 108, and 4 × 108 cycles. Testing included multiple combinations of mean strains (1.5%-9%) and strain amplitudes (0.50%-2.50%) to simulate the multi-strain operating environments encountered in TMVR devices. VAR/EBR Nitinol demonstrated a conservative 130% improvement in 4 × 108-cycle Fatigue Strain Limit (FSL) compared to conventional VAR Nitinol at mean strains between 3% and 5%. The FSL behavior revealed two distinct strain regimes correlating with stress-induced martensitic transformation. Fractographic analysis confirmed elimination of inclusion-initiated fatigue failure, with crack initiation occurring independently of microstructural defects. The ultra-clean microstructure of VAR/EBR Nitinol enables a fundamental shift from flaw-dominated to stress-dominated fatigue behavior, providing unprecedented safety margins for complex transcatheter devices operating across diverse mechanical conditions. This material advancement has broad implications for Class III cardiovascular device design, enabling devices like the HighLife system and other TMVR platforms to meet stringent regulatory durability requirements while maintaining safety across complex multi-strain operating environments.

Intrinsic Ti4Ni2Ox and TiC inclusions are known to affect the fatigue behavior of Nitinol particularly in its ultralong fatigue life; nevertheless, there are few statistical analyses to characterize the inclusion sizes and morphology to show such relationships quantitatively. This investigation characterizes the inclusions in Nitinol from six melt sources with scanning electron microscopy in the backscattered imaging mode in accord with the on-going ASTM Working Document (Determining the Porosity and Inclusion Content of Nickel Titanium Shape-Memory Alloys (NiTi SMAs) Using Automatic Image Analysis). Specifically, the Feret diameter, area fraction, and aspect ratio were measured from N = 36 images from each condition and both orientations. The results from two laboratories resulted in similar trends with respect to longitudinal and transverse inclusion characteristics. The Feret diameters were further analyzed according to ASTM E2283. In the longitudinal direction VAR Nitinol has extreme dimensions of > 270 µm, whereas the VAR/EBR Nitinol has < 8 µm inclusion dimensions.

This study investigates the bending fatigue performance of Vacuum Arc Remelted/Electron Beam Refined (VAR/EBR) Nitinol for cardiovascular applications. Diamond-shaped fatigue specimens were manufactured from ultra-clean VAR/EBR Nitinol tubing with inclusion sizes below 10 μm and tested under physiologically relevant conditions to 100 million cycles. Testing included multiple combinations of mean strains (0–7

The total-life fatigue behavior of Nitinol superelastic wire under uniaxial tension-tension loading is here investigated while monitoring the global stresses and strains. The strain-life (ε/N) fatigue under positive mean strain (εm > 0) and strain ratio (Rε (= εmin/εmax) > 0) conditions is reported under displacement-controlled condition in the mixed austenite–martensite phase region. A total of 383 fatigue tests were conducted with four pre-strains (6 to 10

“Designing” metallic glasses to exhibit properties beyond those offered within the narrow composition ranges where glass formation is possible poses a formidable scientific challenge. This challenge may be tackled by forming composite structures comprising a metallic glass matrix and homogeneously precipitated dendrites, known as “metallic glass matrix composites” (MGMCs). In principle, MGMCs can be designed to exploit the attractive performance characteristics of the metallic glass while alleviating its negative undesirable attributes. In this work we introduce a MGMC development concept for designing color in metallic glass. MGMCs consisting of a white-gold metallic glass matrix with finely dispersed yellow-gold microdendrites are explored. A series of gold MGMCs is developed displaying uniform and visually-unresolved yellow colors over a broad range of chromaticity, along with high overall hardness. This design concept paves the way for the development of a new generation of metal alloys that combine advanced engineering performance with attractive cosmetic attributes.

The requirements imposed by the enormous scale and overall complexity of designing new implants or complete organ regeneration are well beyond the reach of present technology in many dimensions, including nanoscale, as researchers do not yet have the basic knowledge required to achieve these goals. The need for a synthetic implant to address multiple physical and biologic factors imposes tremendous constraints on the choice of suitable materials. There is a strong belief that nanoscale materials will produce a new generation of implant materials with high efficiency, low cost, and high volume. The nanoscale in materials processing is truly a new frontier. Metallic dental implants have been used successfully for decades, but they have serious shortcomings related to their osseointegration and the fact that their mechanical properties do not match those of bone. This paper reviews recent advances in the fabrication of novel coatings and nanopatterning of dental implants. It also provides a general summary of the state of the art in dental implant science and describes possible advantages of nanotechnology for future improvements. The ultimate goal is to produce materials and therapies that will bring state-of-the-art technology to the bedside and improve quality of life and current standards of care.

Owing to a lack of microstructure, glassy materials are inherently strong but brittle, and often demonstrate extreme sensitivity to flaws. Accordingly, their macroscopic failure is often not initiated by plastic yielding, and almost always terminated by brittle fracture. Unlike conventional brittle glasses, metallic glasses are generally capable of limited plastic yielding by shear-band sliding in the presence of a flaw, and thus exhibit toughness-strength relationships that lie between those of brittle ceramics and marginally tough metals. Here, a bulk glassy palladium alloy is introduced, demonstrating an unusual capacity for shielding an opening crack accommodated by an extensive shear-band sliding process, which promotes a fracture toughness comparable to those of the toughest materials known. This result demonstrates that the combination of toughness and strength (that is, damage tolerance) accessible to amorphous materials extends beyond the benchmark ranges established by the toughest and strongest materials known, thereby pushing the envelope of damage tolerance accessible to a structural metal.

The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I+II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and “weakest” microstructural resistance.

A novel biomimetic approach to the design of high‐ performance ceramic/metal composites Maximilien E. Launey 1 , Etienne Munch 1,† , Daan Hein Alsem 1,2 , Eduardo Saiz 1 , Antoni P. Tomsia 1 and Robert O. Ritchie 1,3,  1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 Department of Materials Science and Engineering, University of California, Berkeley, California, 94720, USA Abstract The prospect of extending natural biological design to develop new synthetic ceramic/metal composite materials is examined. Using ice‐templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine‐scale laminated ceramic/metal (bulk) composites that are inexpensive, lightweight, and display exceptional damage‐tolerance properties. Specifically, Al 2 O 3 /Al‐Si laminates with ceramic contents up to ~40 vol.% and with lamellae thicknesses down to 10 μm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa√m at a tensile strength of ~300 MPa. Salient toughening mechanisms are described together with further toughening strategies. Keywords: ceramics; metals; composites; toughness; strength; freeze casting Present address: Manufacture Francaise des Pneumatiques Michelin, 63040 Clermont Ferrand, France Author for correspondence (roritchie@lbl.gov)

In situ mechanical testing coupled with imaging using high-energy synchrotron X-ray diffraction or tomography is gaining in popularity as a technique to investigate micrometer and even sub-micrometer deformation and fracture mechanisms in mineralized tissues, such as bone and teeth. However, the role of the irradiation in affecting the nature and properties of the tissue is not always taken into account. Accordingly, we examine here the effect of X-ray synchrotron-source irradiation on the mechanistic aspects of deformation and fracture in human cortical bone. Specifically, the strength, ductility and fracture resistance (both work-of-fracture and resistance-curve fracture toughness) of human femoral bone in the transverse (breaking) orientation were evaluated following exposures to 0.05, 70, 210 and 630 kGrays (kGy) irradiation. Our results show that the radiation typically used in tomography imaging can have a major and deleterious impact on the strength, post-yield behavior and fracture toughness of cortical bone, with the severity of the effect progressively increasing with higher doses of radiation. Plasticity was essentially suppressed after as little as 70 kGy of radiation; the fracture toughness was decreased by a factor of five after 210 kGy of radiation. Mechanistically, the irradiation was found to alter the salient toughening mechanisms, manifest by the progressive elimination of the bone's capacity for plastic deformation which restricts the intrinsic toughening from the formation "plastic zones" around crack-like defects. Deep-ultraviolet Raman spectroscopy indicated that this behavior could be related to degradation in the collagen integrity.

One of the most intriguing protein materials found in nature is bone, a material composed of assemblies of tropocollagen molecules and tiny hydroxyapatite mineral crystals that form an extremely tough, yet lightweight, adaptive and multifunctional material. Bone has evolved to provide structural support to organisms, and therefore its mechanical properties are of great physiological relevance. In this article, we review the structure and properties of bone, focusing on mechanical deformation and fracture behavior from the perspective of the multidimensional hierarchical nature of its structure. In fact, bone derives its resistance to fracture with a multitude of deformation and toughening mechanisms at many size scales ranging from the nanoscale structure of its protein molecules to the macroscopic physiological scale.