Bowden, Lucy; Monroe, Jacquelyn; Bowden, Anton E.; Jensen, Brian D. (Brigham Young University)
Faculty Advisor: Bowden, Anton (Engineering, Mechanical Engineering); Jensen, Brian (Engineering, Mechanical Engineering)
Previously our lab has shown that carbon-infiltrated carbon nanotube (CI-CNT) surfaces enhance osseointegration and resist biofilm formation, making them attractive possibilities as orthopedic implant materials. For these applications, CI-CNTs and their underlying substrate material must be able to withstand aqueous physiologic conditions. Due to microstructural changes that occur during CI-CNT production, we hypothesized that stainless steel substrate materials experience a loss of their protective, passivating layer, subsequently corroding when immersed in a simulated biological environment. The purpose of the study was to compare corrosion resistance of CI-CNT coated stainless steel substrates to bare stainless steel control samples after two days of incubation in different physiological analog media.
CI-CNTs were grown on 316L stainless steel samples which were sonicated for 20 minutes in isopropyl alcohol and given a 2 minute heat treatment in air at 800°C, followed by a 20 minute growth at the same temperature in ethylene and argon. Carbon infiltration was done for 5 minutes in the same gases at 900°C. The samples were autoclaved and placed into different media including deionized water, phosphor buffered saline solution (PBS), and DMEM culture media. The samples were then incubated for 48 hours at 37°C.
Macroscopic observation showed no obvious signs of corrosion (e.g., discoloration of the liquid media, cloudiness, physical changes in sample appearance) for any of the control samples, or for CI-CNT coated samples in deionized water. In contrast, the CI-CNT coated samples immersed in PBS and culture media exhibited significant discoloration and a cloudy appearance. Subsequent SEM images of the CI-CNT coated samples which had been immersed in culture media and PBS showed foreign residue. Energy dispersive x-ray analysis characterized this residue as having markedly higher levels of sodium and phosphorus than a baseline CI-CNT coated stainless steel sample. SEM images of the bare stainless steel samples and the CI-CNT samples cultured in deionized water showed no signs of corrosion or residue.
Our preliminary results illustrate that media containing salts initiated corrosion of CI-CNT coated stainless steel samples, likely due to disruption of the passivating layer in the substrate. Future work will explore methods for re-establishing the passivating layer in stainless steel materials.