Electrochemical determination of corrosion properties of iron foams prepared by using urea as a spaceholder

Porous biodegradable materials have the potential to serve as temporary orthopedic scaffolds with the ability to degrade spontaneously in the human body environment. Several production methods may be used for their manufacturing, including replication methods, additive manufacturing, or casting. The space-holder method represents a cost-effective production way that can produce highly porous materials with an easily controllable porosity ratio. Since porosity plays an important role in the evaluation of material corrosion and mechanical properties, a series of samples with increasing space-holder (urea) ratio (Fe:Urea - 95: 5, 90:10, 85:15, and 80:20) to the iron were fabricated and tested for their electrochemical corrosion properties. Iron powder and spherical urea particles were used as a starting material, compressed into cylindrical shapes, and sintered at 1120 °C for one hour in a reducing hydrogen atmosphere. Potentiodynamic polarization curves of Fe samples were obtained in Hanks´ solution at 37 °C and pH = 7.4±0.2. A decrease of the corrosion potential (E_corr) with increasing porosity was confirmed in simulated body fluids, suggesting the importance of porosity and its influence on the degradation susceptibility of iron-based biomaterials. Smaller urea addition (5 wt.%) did not significantly affect the corrosion potential when compared to the pure iron prepared without the space-holder addition. However, the mechanical integrity of the samples with a higher Fe-urea ratio (80:20) was not maintained after sample sintering, which also must be addressed during future fabrication of such material.