Biodegradation behaviour of Fe-based alloys in Hanks’ Balanced Salt Solutions: Part I. material characterisation and corrosion testing

Abstract

Research on Fe-based biodegradable alloys for implant applications has increased considerably over the past decade. However, there is limited information on the influence of testing electrolytes on corrosion product formation and general corrosion progress. In this work, the effect of Hanks’ Balanced Salt Solution (HBSS) with or without Ca 2+ on the corrosion of Fe, Fe35Mn and (Fe35Mn)5Ag powder-processed coupons has been studied using potentiodynamic polarisation, Electrochemical Impedance Spectroscopy (EIS), and preliminary localised measurement of pH and dissolved oxygen concentration in close proximity to the metal surface. Both Fe35Mn and (Fe35Mn)5Ag alloys showed accelerated corrosion when compared to pure Fe based on potentiodynamic testing results, with FeMnAg exhibiting the highest corrosion rate in Ca 2+ -containing HBSS. The results indicate that in Ca 2+ -containing HBSS, the formation of a partially protective Ca/P layer decelerates the corrosion progress, whereas the Fe- and Mn-phosphates formed in Ca 2+ -free HBSS do not have the same effect. The Ca/P layer on (Fe35Mn)5Ag experienced a reduction in resistance following several hours of testing, indicating partial loss of its protective effect.

FeMn with Phases of a Degradable Ag Alloy for Residue-Free and Adapted Bioresorbability

“…Thus, further materials such as molybdenum (Mo), zinc (Zn), and iron (Fe) are investigated [ 1 , 2 , 4 , 7 , 10 , 11 , 12 ]. Due to its mechanical properties and biocompatibility, Fe is a promising material [ 10 , 13 , 14 , 15 , 16 ]. Since Fe is a necessary trace element for the human organism, with a needed uptake of 8–27 mg per day corresponding to 9.8 g per year, the amount of Fe released by the dissolution of an osteosynthesis plate with a weight of 2 g over a few months is acceptable [ 17 ].…”

“…However, an adaption of pure Fe is necessary, since the degradation rate is too low, the mechanical properties are insufficient compared to commercially used Fe alloys, and the use of magnetic resonance imaging (MRI) is impossible. [ 3 , 10 , 12 , 18 ] Alloying with manganese (Mn) is a promising approach to overcome these limitations [ 13 , 14 , 19 , 20 ]. Mn stabilizes the paramagnetic austenitic structure, enabling MRI and improving the mechanical properties.…”

“…Achieving a reliable and suited degradation under all possible conditions is challenging, since the degradation of Fe-based alloys strongly depends on the ambient conditions. The degradation is affected by the ingredients of the solution, the pH value, which determines the solubility of the corrosion products, and the amount of dissolved gases, such as oxygen (O), that is required for the cathodic reaction [ 14 , 33 , 35 , 37 , 44 ]. For implant design, the slowest degradation must guarantee a sufficient supporting effect for healing, while the fastest degradation must enable the dissolution in a defined period.…”

Stress-Induced Dual-Phase Structure to Accelerate Degradation of the Fe Implant

“…41 Similarly, the double-layer capacitance (CPE f ) and adsorbed film resistance (R f ) were related to the capacitance and resistance behavior at the interface of the oxide layer and metal substrate, respectively. 42 All the fitting parameters are listed in Table 1. The R s did not vary notably for all three alloys.…”

“…The double-layer capacitance (CPE dl ) and the charge-transfer resistance ( R ct ) reflected the capacitance and resistance behavior of the electrolyte–oxide film . Similarly, the double-layer capacitance (CPE f ) and adsorbed film resistance ( R f ) were related to the capacitance and resistance behavior at the interface of the oxide layer and metal substrate, respectively . All the fitting parameters are listed in Table .…”