The Suitability of Zn–1.3%Fe Alloy as a Biodegradable Implant Material

Abstract

Efforts to develop metallic zinc for biodegradable implants have significantly advanced following an earlier focus on magnesium (Mg) and iron (Fe). Mg and Fe base alloys experience an accelerated corrosion rate and harmful corrosion products, respectively. The corrosion rate of pure Zn, however, may need to be modified from its reported~20 µm/year penetration rate, depending upon the intended application. The present study aimed at evaluating the possibility of using Fe as a relatively cathodic biocompatible alloying element in zinc that can tune the implant degradation rate via microgalvanic effects. The selected Zn-1.3wt %Fe alloy composition produced by gravity casting was examined in vitro and in vivo. The in vitro examination included immersion tests, potentiodynamic polarization and impedance spectroscopy, all in a simulated physiological environment (phosphate-buffered saline, PBS) at 37 • C. For the in vivo study, two cylindrical disks (seven millimeters diameter and two millimeters height) were implanted into the back midline of male Wister rats. The rats were examined post implantation in terms of weight gain and hematological characteristics, including red blood cell (RBC), hemoglobin (HGB) and white blood cell (WBC) levels. Following retrieval, specimens were examined for corrosion rate measurements and histological analysis of subcutaneous tissue in the implant vicinity. In vivo analysis demonstrated that the Zn-1.3%Fe implant avoided harmful systemic effects. The in vivo and in vitro results indicate that the Zn-1.3%Fe alloy corrosion rate is significantly increased compared to pure zinc. The relatively increased degradation of Zn-1.3%Fe was mainly related to microgalvanic effects produced by a secondary Zn 11 Fe phase.

Alloying design of biodegradable zinc as promising bone implants for load-bearing applications

“…Apart from the solid solution and refined grain, tensile twin was a key factor affecting the mechanical property of as-extruded Zn-Mn alloys 49 . Although Ca and Sr showed no strengthening effect on Zn in this study, an increased tensile strength of Zn-Ca, Zn-Sr, and Zn-Fe alloys with higher contents were observed elsewhere 16,50 . Alloying with selected elements here increased the degradation rates of Zn to varying degrees.…”

Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process

“…The corresponding electrical equivalent circuits, along with the related fitted parameters for the initial and long-term immersion, are shown in Figure 13a,b, respectively. The fitted parameters include the following factors: R1-solution resistance, R2 and Q1 (capacitor), related to the double layer [19,20], R3 and Q2, corresponding to charge transfer resistance and capacitor, respectively, which are related to the effect of corrosion products and the time constant that appeared in the low frequency region [21,22]. Stress corrosion examination of the printed ER70S-6 and reference ST-37 alloys by slow strain rate testing (SSRT) in 3.5% NaCl solution in terms of UTS and elongation are shown in Figures 14 and 15, respectively.…”

The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

“…The related electrical equivalent circuit, as well as the fitted parameters, are shown in Figure 6. The fitted parameters were: R1, solution resistance; R2 and C1 represent the double layer [29]; R3 and C2 represent the charge transfer resistance and capacitor [30].…”

“…The related electrical equivalent circuit, as well as the fitted parameters, are shown in Figure 6. The fitted parameters were: R1, solution resistance; R2 and C1 represent the double layer [29]; R3 and C2 represent the charge transfer resistance and capacitor [30]. The high cycle fatigue strengths of additively manufactured ER70S-6 alloy and its counterpart ST-37 alloy, in air and in 3.5% NaCl solution, in terms of their S-N curves, are shown in Figure 7a,b.…”