Mechanical Analysis and Corrosion Analysis of Zinc Alloys for Bioabsorbable Implants for Osteosynthesis

Abstract

Zinc alloys have recently been researched intensely for their great properties as bioabsorbable implants for osteosynthesis. Pure zinc (Zn) itself has relatively poor strength, which makes it insufficient for most clinical use. Research has already proven that the mechanical strength of zinc can be enhanced significantly by alloying it with silver. This study evaluated zinc silver alloys (ZnAg) as well as novel zinc silver titanium alloys (ZnAgTi) regarding their mechanical properties for the use as bioabsorbable implants. Compared to pure zinc the mechanical strength was enhanced significantly for all tested zinc alloys. The elastic properties were only enhanced significantly for the zinc silver alloys ZnAg6 and ZnAg9. Regarding target values for orthopedic implants proposed in literature, the best mechanical properties were measured for the ZnAg3Ti1 alloy with an ultimate tensile strength of 262 MPa and an elongation at fracture of 16%. Besides the mechanical properties, the corrosion rates are important for bioabsorbable implants. This study tested the corrosion rates of zinc alloys in PBS solution (phosphate buffered solution) with electrochemical corrosion measurement. Zinc and its alloys showed favorable corrosion rates, especially in comparison to magnesium, which has a much lower degradation rate and no buildup of hydrogen gas pockets during the process. Altogether, this makes zinc alloys highly favorable for use as material for bioabsorbable implants for osteosynthesis.

Keywords: biodegradation; corrosion testing; mechanical stability; tensile testing; zinc alloy; zinc silver; zinc titanium.

Figure 1

Corrosion sample attached to sample holder.

Figure 2

Schematic layout of the corrosion measuring cell.

Figure 3

Example of a Tafel fitting on log current-potential curve.

Figure 4

Averaged stress–strain curves of all tensile tests with the ZwickRoell Z005 materials testing machine and recorded with TestXpert3, with (a) pure zinc, (b) ZnTi0.5 alloy, (c) zinc silver alloys, and (d) zinc silver titanium alloys.

Figure 5

Mean difference of corrosion current after ANOVA between zinc and the tested alloys.

Figure 6

Comparison of elongation at fracture (A) and ultimate tensile strength (UTS) of the alloys measured in this study (blue icons) with measurements reported in the literature [30,52,53,54,55,56,57,58]. The area highlighted in green corresponds to the target values given in the literature of an elongation at fracture between 15 to 20% and an ultimate tensile strength between 200 to 300 MPa.

Figure 7

Corrosion rates of zinc and zinc alloys measured in electrochemical corrosion testing in different media [21,22,30,31].