The influence of Desulfovibrio desulfuricans bacteria on a Ni-Ti alloy: electrochemical behavior and surface analysis

The combined effect of carbon starvation and exogenous riboflavin accelerated the Pseudomonas aeruginosa-induced nickel corrosion

The primary objective of this study is to elucidate the synergistic effect of an exogenous redox mediator and carbon starvation on the microbiologically influenced corrosion (MIC) of metal nickel (Ni) by nitrate reducing Pseudomonas aeruginosa. Carbon source (CS) starvation markedly accelerates Ni MIC by P. aeruginosa. Moreover, the addition of exogenous riboflavin significantly decreases the corrosion resistance of Ni. The MIC rate of Ni (based on corrosion loss volume) is ranked as: 10 % CS level + riboflavin > 100 % CS level + riboflavin > 10 % CS level > 100 % CS level. Notably, starved P. aeruginosa biofilm demonstrates greater aggressiveness in contributing to the initiation of surface pitting on Ni. Under CS deficiency (10 % CS level) in the presence of riboflavin, the deepest Ni pits reach a maximum depth of 11.2 μm, and the corrosion current density (icorr) peak at approximately 1.35 × 10-5 A·cm-2, representing a 2.6-fold increase compared to the full-strength media (5.25 × 10-6 A·cm-2). For the 10 % CS and 100 % CS media, the addition of exogenous riboflavin increases the Ni MIC rate by 3.5-fold and 2.9-fold, respectively. Riboflavin has been found to significantly accelerate corrosion, with its augmentation effect on Ni MIC increasing as the CS level decreases. Overall, riboflavin promotes electron transfer from Ni to P. aeruginosa, thus accelerating Ni MIC.

Carbon starvation considerably accelerated nickel corrosion by Desulfovibrio vulgaris

Carbon starvation can affect the activity of microbes, thereby affecting the metabolism and the extracellular electron transfer (EET) process of biofilm. In the present work, the microbiologically influenced corrosion (MIC) behavior of nickel (Ni) was investigated under organic carbon starvation by Desulfovibrio vulgaris. Starved D. vulgaris biofilm was more aggressive. Extreme carbon starvation (0% CS level) reduced weight loss due to the severe weakening of biofilm. The corrosion rate of Ni (based on weight loss) was sequenced as 10% CS level > 50% CS level > 100 CS level > 0% CS level. Moderate carbon starvation (10% CS level) caused the deepest pit of Ni in all the carbon starvation treatments, with a maximal pit depth of 18.8 μm and a weight loss of 2.8 mg·cm-2 (0.164 mm·y-1). The corrosion current density (icorr) of Ni for the 10% CS level was as high as 1.62 × 10-5 A·cm-2, which was approximately 2.9-fold greater than the full-strength medium (5.45 × 10-6 A·cm-2). The electrochemical data corresponded to the corrosion trend revealed by weight loss. The various experimental data rather convincingly pointed to the Ni MIC of D. vulgaris following the EET-MIC mechanism despite a theoretically low Ecell value (+33 mV).

Enhanced corrosion resistance, antibacterial properties, and biocompatibility by hierarchical hydroxyapatite/ciprofloxacin-calcium phosphate coating on nitrided NiTi alloy

Multi-functional hierarchical coatings are deposited on the nitrided NiTi alloy. The nitrided layer is first deposited by nitrogen plasma immersion ion implantation and a middle layer containing porous hydroxyapatite and ciprofloxacin (Cip) is produced before the top calcium phosphate coating is deposited by the sol-gel method. The thicknesses of the coating and nitrided intermediate layer are about 1.54 μm and 160 nm, respectively and Cip penetrates to a depth of about 530 nm. Calcium phosphate reduces surface defects resulting in a surface roughness of 17 ± 2 nm compared to 34 ± 5 nm of the porous hydroxyapatite coating. The corrosion resistance is improved due to reduced defects and localized corrosion as manifested by the decrease in the Ni²⁺ release rate by 11.6% from 0.0198 to 0.0175 mg L^-1 cm^-2. The bacterial resistance against E. coli is also improved by about 88 times on account of Cip release and good biocompatibility is confirmed by proliferation of MC3T3 cells. This multi-functional hierarchical coating has large potential in orthopedic and dental applications.