Evaluation of wrought Zn–Al alloys (1, 3, and 5 wt % Al) through mechanical and in vivo testing for stent applications

Abstract

Special high grade zinc and wrought zincaluminum (Zn-Al) alloys containing up to 5.5 wt % Al were processed, characterized, and implanted in rats in search of a new family of alloys with possible applications as bioabsorbable endovascular stents. These materials retained roll-induced texture with an anisotropic distribution of the second-phase Al precipitates following hot-rolling, and changes in lattice parameters were observed with respect to Al content. Mechanical properties for the alloys fell roughly in line with strength (190-240 MPa yield strength; 220-300 MPa ultimate tensile strength) and elongation (15-30%) benchmarks, and favorable elastic ranges (0.19-0.27%) were observed. Intergranular corrosion was observed during residence of Zn-Al alloys in the murine aorta, suggesting a different corrosion mechanism than that of pure zinc. This mode of failure needs to be avoided for stent applications because the intergranular corrosion caused cracking and fragmentation of the implants, although the composition of corrosion products was roughly identical between nonand Al-containing materials. In spite of differences in corrosion mechanisms, the cross-sectional reduction of metals in murine aorta was nearly identical at 30-40% and 40-50% after 4.5 and 6 months, respectively, for pure Zn and Zn-Al alloys. Histopathological analysis and evaluation of arterial tissue compatibility around Zn-Al alloys failed to identify areas of necrosis, though both chronic and acute inflammatory indications were present.

The Prospects of Zinc as a Structural Material for Biodegradable Implants—A Review Paper

“…The in vivo implantation of Zn-1Li demonstrated positive biocompatibility, with no significant differences in serum zinc observed before, and 1-3 months after, implantation. According to Bowen et al [52], biodegradation of a Zn-Al stent, with a weight of~50 mg and a 5 wt % Al content-assuming bioabsorption of the entire stent in 2 years and a stable corrosion rate-would result in a daily intake of~0.003 mg of Al, substantially below the~10 mg daily intake for an average person. In their in vivo studies [20,52], Zn-Al (1, 3 and 5% Al) strips were implanted in the wall of the abdominal aorta of adult Sprague-Dawley rats.…”

“…According to Bowen et al [52], biodegradation of a Zn-Al stent, with a weight of~50 mg and a 5 wt % Al content-assuming bioabsorption of the entire stent in 2 years and a stable corrosion rate-would result in a daily intake of~0.003 mg of Al, substantially below the~10 mg daily intake for an average person. In their in vivo studies [20,52], Zn-Al (1, 3 and 5% Al) strips were implanted in the wall of the abdominal aorta of adult Sprague-Dawley rats. The Zn-Al systems exhibited acceptable compatibility with surrounding arterial tissue, as the histopathological analysis failed to identify necrotic tissue in the samples examined, although indications of chronic and acute inflammation were both identified.…”

Long-term surveillance of zinc implant in murine artery: Surprisingly steady biocorrosion rate

“…The elongation to failure of pure Zn (60–80%) is, on the other hand, far superior relative to Mg (13%) and Fe (18%) [19]. Alloying of Zn can improve its strength to the level of Fe and above [39–41], with elongation to failure remaining above values characteristic for pure Mg and Fe [19]. Studies so far on Zn as an experimental stent material have shown good biocompatibility and a rate of degradation between 10–20 µm/yr, which is similar to the 20 µm/yr benchmark value for an ideal bioabsorable material [42,43].…”

Preparation and Characterization of Zinc Materials Prepared by Powder Metallurgy

“…The influence of the preparation method and its parameters on mechanical properties is studied only marginally [17,[27][28][29][30].…”