The use of tungsten as a chronically implanted material

Abstract

This review paper shows that tungsten should not generally be used as a chronically implanted material. The metal has a long implant history, from neuroscience, vascular medicine, radiography, orthopaedics, prosthodontics, and various other fields, primarily as a result of its high density, radiopacity, tensile strength, and yield point. However, a crucial material criterion for chronically implanted metals is their long-term resistance to corrosion in body fluids, either by inherently noble metallic surfaces, or by protective passivation layers of metal oxide. The latter is often assumed for elemental tungsten, with references to its 'inertness' and 'stability' common in the literature. This review argues that in the body, metallic tungsten fails this criterion, and will eventually dissolve into the soluble hexavalent form W, typically represented by the orthotungstate [Formula: see text] (monomeric tungstate) anion. This paper outlines the metal's unfavourable corrosion thermodynamics in the human physiological environment, the chemical pathways to either metallic or metal oxide dissolution, the rate-limiting steps, and the corrosion-accelerating effects of reactive oxidising species that the immune system produces post-implantation. Multiple examples of implant corrosion have been reported, with failure by dissolution to varying extents up to total loss, with associated emission of tungstate ions and elevated blood serum levels measured. The possible toxicity of these corrosion products has also been explored. As the field of medical implants grows and designers explore novel solutions to medical implant problems, the authors recommend the use of alternative materials.

Processing of WC/W composites for extreme environments by colloidal dispersion of powders and SPS sintering

“…It is in this context where the high melting point (3420 °C) and high density (19,3 g/cm 3 ) stand out as an alternative. These physical characteristics are originated from its position in the group VI of the periodic table, sharing with U, Re, Pt, Ir, and Os to be the densest elements [5], and from the strong unsaturated covalent bonds between the valence 5d orbitals, which provide metallic tungsten the largest cohesive energy of all the pure elements (7,9-10,09 eV/atom), including diamond (carbon). In fact, tungsten is considered the most ceramic of the metals, as it is a refractory metal with a low thermal expansion coefficient (4,3 × 10 −6 /°C).…”

An implantable system for long-term assessment of atrial fibrillation substrate in unanesthetized rats exposed to underlying pathological conditions

“…On the contrary, at 4 W animals in the non-isolated group had small but significant increase in AF induction compared to the original (Isolated) sham group. Specifically, we suspected that tungsten, which was recently suggested to have unfavorable long-term effects as a chronically implanted material 35 , was involved in this phenomenon. To address this possibility, a new type of MBHE was fabricated.…”

Synovial Fluid pH Sensor for Early Detection of Prosthetic Hip Infections

“…Tantalum and tungsten were chosen as the preferred metals in the development of the sensor due to their biocompatibility, corrosion resistance and radio‐opacity (high atomic number and density). [ 33–35 ] In order for the sensor to detect hip infections in vivo, it needs to measure physiologically relevant pH changes indicating infection with a precision of ≈0.1 pH units in the range of pH 6.7–7.5, with an appropriate response rate (less than 12 h to facilitate physiological measurements and preferably less than 1 h to facilitate experimental study). For in vivo use, the sensor needs to be resistant to changes in temperature and ionic strength and maintain its performance in synovial fluid with minimal effect from biofouling.…”