Abstract
A β-Ta nanocrystalline coating was engineered onto a Ti-6Al-4V substrate using a double cathode glow discharge technique to improve the corrosion resistance and bioactivity of this biomedical alloy. The new coating has a thickness of ~40 μm and exhibits a compact and homogeneous structure composed of equiaxed β-Ta grains with an average grain size of ~22 nm, which is well adhered on the substrate. Nanoindentation and scratch tests indicated that the β-Ta coating exhibited high hardness combined with good resistance to contact damage. The electrochemical behavior of the new coating was systematically investigated in Hank’s physiological solution at 37 °C. The results showed that the β-Ta coating exhibited a superior corrosion resistance as compared to uncoated Ti-6Al-4V and commercially pure tantalum, which was attributed to a stable passive film formed on the β-Ta coating. The in vitro bioactivity was studied by evaluating the apatite-forming capability of the coating after seven days of immersion in Hank’s physiological solution. The β-Ta coating showed a higher apatite-forming ability than both uncoated Ti-6Al-4V and commercially pure Ta, suggesting that the β-Ta coating has the potential to enhance functionality and increase longevity of orthopaedic implants.
Highlights
With the worldwide rapidity of the population aging process, a significant increase in the incidence of musculoskeletal diseases that directly impacts the quality of life for aged persons, such as osteoporosis, osteoarthritis and degenerative joint disease, has prompted a rapidly expanding demand for materials for hard tissue replacement
The presence of the (002) texture is frequently observed on β-Ta coatings
Compared with uncoated Ti-6Al-4V and commercially pure Ta, the β-Ta coating exhibits wider frequency region for the linear relationship of log|Z| to log f and for the phase angle maximum plateau, denoting that the passive film formed on the β-Ta coating is more insulating and protective than those for the two reference samples
Summary
With the worldwide rapidity of the population aging process, a significant increase in the incidence of musculoskeletal diseases that directly impacts the quality of life for aged persons, such as osteoporosis, osteoarthritis and degenerative joint disease, has prompted a rapidly expanding demand for materials for hard tissue replacement. Amongst the suitable implantable materials in clinical practice, titanium-based alloys have attracted a lot of interest for load bearing implant applications outperforming more conventional stainless steels and cobalt-based alloys, due to their combination of outstanding characteristics, such as high specific strength, high immunity to corrosion and enhanced biocompatibility under in vivo conditions [1,2]. Excellent clinical results have been demonstrated with these materials, they suffer from several inherent drawbacks, including poor bioactivity, insufficient corrosion resistance in body fluids and inferior tribological characteristics, to cause long-term health problems. Metals 2016, 6, 221 body environment containing chloride ions and proteins, is very aggressive, in vivo corrosion of titanium-based implants is inevitable when exposed to such a harsh environment, thereby metal ions release from implants into body fluids [4,5]. The released ions are found to cause allergic and toxic reactions [5], and show potential negative effects on osteoblast behavior [6]
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