Improving the radiopacity of Fe–Mn biodegradable metals by magnetron-sputtered W–Fe–Mn–C coatings: Application for thinner stents

In this exploratory work, micrometric radiopaque W–Fe–Mn–C coatings were produced by magnetron sputtering plasma deposition, for the first time, with the aim to make very thin Fe–Mn stents trackable by fluoroscopy. The power of Fe–13Mn-1.2C target was kept constant at 400 W while that of W target varied from 100 to 400 W producing three different coatings referred to as P100, P200, P400. The effect of the increased W power on coatings thickness, roughness, structure, corrosion behavior and radiopacity was investigated. The coatings showed a power-dependent thickness and W concentration, different roughness values while a similar and uniform columnar structure. An amorphous phase was detected for both P100 and P200 coatings while γ-Fe, bcc-W and W3C phases found for P400. Moreover, P200 and P400 showed a significantly higher corrosion rate (CR) compared to P100. The presence of W, W3C as well as the Fe amount variation determined two different micro-galvanic corrosion mechanisms significantly changing the CR of coatings, 0.26 ± 0.02, 59.68 ± 1.21 and 59.06 ± 1.16 μm/year for P100, P200 and P400, respectively. Sample P200 with its most uniform morphology, lowest roughness (RMS = 3.9 ± 0.4 nm) and good radiopacity (∼6%) appeared the most suitable radiopaque biodegradable coating investigated in this study.
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Highlights • Three W–Fe–Mn–C coatings (P100, P200, P400) were developed by magnetron sputtering. • Coatings showed a columnar structure and power-dependent thickness and W concentration. • Thicknesses from 0.9 ± 0.2 to 1.8 ± 0.2 μm and RMS from 3.9 ± 0.4 to 54.3 ± 8.1 nm were found for P100, P200, P400, resp. • The amorphous phase of P100, P200 and γ-Fe, bcc-W and W3C of P400 significantly affected the CR. • The most uniform morphology, lowest roughness (3.9 ± 0.4 nm) and good radiopacity (∼6%) were found for P200.