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The role of zinc in the biocorrosion behavior of resorbable Mg‒Zn‒Ca alloys.
Journal article

The role of zinc in the biocorrosion behavior of resorbable Mg‒Zn‒Ca alloys.

  • Cihova M Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland. Electronic address: martina.cihova@mat.ethz.ch.
  • Martinelli E Department of Orthopaedics, Medical University Graz, 8036 Graz, Austria.
  • Schmutz P Laboratory for Joining Technologies and Corrosion, EMPA, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
  • Myrissa A Department of Orthopaedics, Medical University Graz, 8036 Graz, Austria.
  • Schäublin R Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.
  • Weinberg AM Department of Orthopaedics, Medical University Graz, 8036 Graz, Austria.
  • Uggowitzer PJ Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.
  • Löffler JF Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland. Electronic address: joerg.loeffler@mat.ethz.ch.
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  • 2019-09-21
Published in:
  • Acta biomaterialia. - 2019
Biocorrosion
Electrochemistry
Magnesium alloy
Microstructure
Nano-galvanic coupling
Redeposition
Transmission electron microscopy
Alloys
Animals
Body Fluids
Bone and Bones
Calcium
Corrosion
Electricity
Electrochemical Techniques
Electrodes
Hydrogen
Implants, Experimental
Magnesium
Rats, Sprague-Dawley
Thermodynamics
Tomography, X-Ray Computed
Zinc
English Zinc- and calcium-containing magnesium alloys, denominated ZX alloys, excel as temporary implant materials because of their composition made of physiologically essential minerals and lack of commonly used rare-earth alloying elements. This study documents the specific role of nanometric intermetallic particles (IMPs) on the in vitro and in vivo biocorrosion behavior of two ZX-lean alloys, Mg‒Zn1.0‒Ca0.3 (ZX10) and Mg‒Zn1.5‒Ca0.25 (ZX20) (in wt.%). These alloys were designed according to thermodynamic considerations by finely adjusting the nominal Zn content towards microstructures that differ solely in the type of phase composing the IMPs: ZX10, with 1.0 wt.% Zn, hosts binary Mg2Ca-phase IMPs, while ZX20, with 1.5 wt.% Zn, hosts ternary IM1-phase IMPs. Electrochemical methods and the hydrogen-gas evolution method were deployed and complemented by transmission electron microscopy analyses. These techniques used in concert reveal that the Mg2Ca-type IMPs anodically dissolve preferentially and completely, while the IM1-type IMPs act as nano-cathodes, facilitating a faster dissolution of ZX20 compared to ZX10. Additionally, a dynamically increasing cathodic reactivity with progressing dissolution was observed for both alloys. This effect is explained by redeposits of Zn on the corroding surface, which act as additional nano-cathodes and facilitate enhanced cathodic reaction kinetics. The higher degradation rate of ZX20 was verified in vivo via micro-computed tomography upon implantation of both materials into femurs of Sprague DawleyⓇ rats. Both alloys were well integrated with direct bone‒implant contact observable 4 weeks post operationem, and an appropriately slow and homogeneous degradation could be observed with no adverse effects on the surrounding tissue. The results suggest that both alloys qualify as new temporary implant materials, and that a minor adjustment of the Zn content may function as a lever for tuning the degradation rate towards desired applications. STATEMENT OF SIGNIFICANCE: In Mg‒Zn‒Ca (ZX)-lean alloys Zn is the most electropositive element, and thus requires special attention in the investigation of biocorrosion mechanisms acting on these alloys. Even a small increase of only 0.5 wt.% Zn is shown to accelerate the biodegradation rate in both simulated body conditions and in vivo. This is possible due to Zn's role in influencing the type of intermetallic particles (IMPs) in these alloys. These IMPs in turn, even though minute in size, are shown to govern the biocorrosion behavior on the macroscopic scale. The deep understanding gained in this study on the role of Zn and of the IMP type it governs is crucial to ensuring a safe and controllable implant degradation.
Language
  • English
Open access status
closed
Identifiers
Persistent URL
https://sonar.ch/global/documents/237558
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