The use of multiple pseudo-physiological solutions to simulate the degradation behavior of pure iron as a metallic resorbable implant: a surface-characterization study

Abstract

Understanding the interactions of a pure iron surface with biological elements, such as ions and proteins in an aqueous medium, is essential for an accurate in vitro assessment of corrosion patterns. In fact, the synergy of chlorides, carbonates, phosphates and complex organic molecules present in the body environment is a key factor affecting both in vivo and in vitro degradation of materials, especially iron and its alloys. The aim of this work was the assessment of degradation patterns of pure iron in 5 commercial pseudo-physiological solutions by a thorough study of degraded surface chemistry and morphology. It also provides a methodological basis to understand the short-term degradation mechanism of degradable iron depending on the surrounding physiological media. The standard static immersion corrosion test was modified to adapt the procedure to pseudo-physiological solutions. After a 14-day static immersion test, the surfaces of samples were investigated by scanning electron microscopy, stylus profilometry and atomic force microscopy techniques. The chemistry and phase composition of the degraded layers were evaluated, respectively, by X-ray photoelectron spectrometry and X-ray diffractometry. The morphology and composition of the degradation layers were found to be different for the test-solutions: for phosphate-rich solutions, the formation of an adherent passive layer was found; degradation mechanisms related to general corrosion were predominant for all the other solutions. In conclusion, the chemical composition of the used medium plays a fundamental role in the degradation pattern of pure iron, so that direct comparisons of solutions with different ion concentrations, as reported in the literature, need to be carefully assessed.

Long-term in vitro degradation behaviour of Fe and Fe/Mg2Si composites for biodegradable implant applications

“…2c). 19 Similarly, aer 50 days of an experiment, the degraded surfaces of composites consist of siderite and goethite ( Fig. 2b and c).…”

“…29 Hanks' modied solution is one of the most common simulated body uids to perform in vitro degradation tests. 3,5,19 The corrosion pattern of Fe and Fe/Mg 2 Si composites in this solution can be used to predict their in vivo behavior because its ionic concentration is similar to that in blood plasma. 22 The degradation of Fe is a phenomenon triggered by surface conditions and it depends on the chemical composition of the corrosive medium, pH, temperature, and solubility of metallic ions released from the substrate.…”

“…22 The degradation of Fe is a phenomenon triggered by surface conditions and it depends on the chemical composition of the corrosive medium, pH, temperature, and solubility of metallic ions released from the substrate. 19 When Fe is immersed in a solution, it is oxidized to Fe 2+ based on the following reaction: 30 Fe / Fe 2+ + 2e…”

“…36 Other researchers reported that the presence of phosphates in the solution promotes Fe passivation, resulting in the formation of phosphates in either amorphous or crystalline form. 19,34,37 It was reported by Refait et al 37 that the amorphous deposit created on the Fe surface was made of nanoparticles revealing a similar structure to that of carbonatebased green rust. The adsorption of phosphate species on these nanoparticles hindered their growth and transformation into a fully ripened Fe carbonates.…”

“…The latest efforts have brought the development of several testing strategies, that predict the evolution of Fe corrosion and release. [19][20][21] A variety of parameters affect the Fe ion release and there is no agreement regarding the quantitative extent that each factor contributes. As a result, a direct comparison between the reported in the literature degradation rates for Fe and Fe-based BMs remains impossible.…”