Evolution of degradation mechanism and fixation strength of biodegradable Zn-Cu wire as sternum closure suture: An in vitro study.

This work reports the first in vitro study on the in-situ biodegradation behaviour and the evolution of fixation strength of Zn-Cu alloy wires in a simulated sternum closure environment. Zn-Cu wires were used to reapproximate the partial bisected sternum models, and their fixation effect was compared with traditional surgical grade 316 L stainless steel (SS) wires in terms of fixation rigidity, critical load, first/ultimate failure characteristics. The metal sutures were then immersed in Hank's balanced salt solution for 12 weeks immersion period, and their corrosion behaviours assessed. Zn-Cu wires showed similar fixation rigidity at 70.89 ± 6.97 N/mm as SS, but the critical load, first failure and ultimate failure characteristics were inferior to SS. The key challenges that limited the fixation effect of the Zn-Cu wires were poor mechanical strength, short elastic region, and strain softening behaviours, which resulted in poor load-bearing capabilities and reduced the knot security of the sutures. The in-situ biodegradation of the Zn-Cu suture was accompanied by the early onset of localised corrosion within the twisted knot and the section located next to the incision line. Crevice corrosion and strain-induced corrosion were the dominant mechanisms in the observed localised corrosion. The localised corrosion on the Zn-Cu sutures did not lead to a significant shift in fixation rigidity, critical load and the first failure characteristics. The findings suggest that the Zn-based biodegradable metallic wires could be a promising sternum closure suture material once the limitations in mechanical characteristics are addressed.