Abstract: BACKGROUND: Due to the complex physiological environment of the human body, a wide variety of simulated physiological fluids have been chosen for the current degradation experiments. Therefore, it is of great interest to analyze the degradation behavior of Mg-Zn-Ca alloys in different simulated body fluid environments.
OBJECTIVE: To investigate the degradation process and property changes of Mg-Zn-Ca alloy in different simulated body fluids, and to clarify the influence of Ca content and simulated body fluid type on the alloy.
METHODS: Mg-Zn-Ca alloys with calcium content of 0.2%, 0.5% and 1% were prepared by melting extrusion molding process and were named Mg-Zn-0.2Ca, Mg-Zn-0.5Ca and Mg-Zn-1Ca alloys in turn, with Mg-Zn alloy as the control. The prepared alloys were placed into three simulated body liquids (physiological saline, PBS and Hank’s solution), and the morphology, compositional changes, mass loss, pH value and mechanical properties were characterized and analyzed during the degradation.
RESULTS AND CONCLUSION: (1) With the extension of degradation time, a large number of nanoscale lamellae and columnar structures were generated on the surface of the degraded alloy, and the main components were MgO and Mg(OH)2. The degradation rate of the four kinds of alloys in physiological saline was the fastest, and that in Hank’s solution was the slowest. The degradation rate in physiological saline was as follows: Mg-Zn < Mg-Zn-0.2Ca < Mg-Zn-0.5Ca < Mg-Zn-1Ca. The degradation rate in PBS and Hank’s solution was as follows: Mg-Zn < Mg-Zn-0.2Ca ≈ Mg-Zn-0.5Ca < Mg-Zn-1Ca. (2) With the extension of degradation time, all four kinds of alloys had a certain mass loss. The degradation in physiological saline was the fastest; the degradation in Hank’s solution and PBS was slow, and in the same simulated body fluid, with the increase of calcium content in the alloy, the corrosion rate of the alloy was obviously accelerated. (3) The pH rise was mainly concentrated in 1 day and slowed down after that, and the pH change was the largest in PBS. In the same simulated body fluid, with the increase of calcium content in the alloy, the pH value in the degradation environment increased significantly. (4) In the initial state, the elastic modulus of all Mg-Zn-Ca alloys was higher than that of Mg-Zn alloys. After being placed in simulated body fluids, the elastic modulus of the four alloys decreased with the extension of degradation time, and the decrease was most obvious in physiological saline. (5) In conclusion, a small amount of Ca addition improved the mechanical properties of Mg-Zn-Ca alloy. A small amount of Ca does not accelerate the degradation rate of the alloy, but excessive Ca accelerates the degradation rate of the alloy. During the degradation, the effect of physiological saline simulated body fluid on the mechanical strength of the alloy was the most significant.

Key words: Mg-Zn-Ca alloy, bone defect, degradation in vitro, mechanical property, simulated body fluid