Mechanical characteristics and biocorrosion behaviour of AS-CAST Zn-3Cu-Al alloys for cardiovascular bioabsorbable devices

Abstract

In this study, the biomechanical and biocorrosion behaviour of as-cast Zn-3Cu-xAl (x = 0, 1, and 2 wt%) alloys for potential application as biodegradable cardiovascular stents was investigated. The alloys were manufactured by liquid metallurgy processing employing metal casting practices, while Scanning electron microscopy (SEM), X-ray diffractometry (XRD), hardness, tensile properties, fracture toughness, and invitro biodegradation rate evaluation in physiological saline solution (0.9% w/v sodium chloride and 5% w/v glucose), were yardsticks used to assess the alloys’ material characteristics. The results show that alloys all consist predominantly of ƞ Zn solid solution phase; while Cu5Zn8; Al4Cu9; and Al4Cu9, AlCu; were the intermetallic phases also identified as complementary phase constituents in the Zn-3Cu, Zn-3Cu-1Al, and Zn-3Cu-2Al alloys, respectively. The 1 and 2 wt% addition of Al in the Zn-3Cu alloy system, resulted in 4.52 and 21.89% increase in hardness, 4.46 and 35.17% increase in ultimate tensile strength, 5.09 and 36.88% increase in specific strength, 2.18 and 34.74% increase in fracture toughness, but 10.5 and 16.6% decrease in percentage elongation, respectively. The improved strength characteristics of the alloy compositions containing Al were attributed to matrix strengthening (due to solid solution strengthening), phase hardening and particle hardening effects (from the intermetallic phases) facilitated by the Al addition. Furthermore, the rate of in vitro corrosion decreased for the alloy compositions containing Al in comparison to the Zn-3Cu alloy, with the Zn-3Cu-1Al composition exhibiting the least biodegradation rate. The strength, toughness, ductility and biocorrosion property balance exhibited by the Zn-3Cu-1Al and Zn-3Cu-2Al alloy compositions make them promising candidates for further consideration for cardiovascular stent applications.