Corrosion property of vitamin D loaded nanotubes for bio-implants application in an in vitro environment

Abstract

Event Abstract Back to Event Corrosion property of vitamin D loaded nanotubes for bio-implants application in an in vitro environment Sweetu Patel1, Cortino Sukotjo2, Christos Takoudis3, Mathew Mathew4, Farid Amirouche5, Craig Friedrich1 and Tolou Shokuhfar1, 3 1 Michigan Technological University, Mechanical Engineering, United States 2 University of Illinois at Chicago, Restorative Dentistry, United States 3 University of Illinois at Chicago, Bioengineering, United States 4 Rush University Medical Center, Orthopaedics, United States 5 University of Illinois at Chicago, Orthopaedics, United States Introduction: In this study, Ti6Al4V surface has been functionalized with TiO2 nanotubes (TNTs), which has a biomimetic topography that resembles the porous bone morphology structure. Additionally, these TNTs are loaded with Vitamin D, which plays an essential role in homeostasis of the bone remodeling[1]. Previously, various beneficial factors of TNTs have been studied; however, the corrosion property of drug loaded TNTs has yet to be investigated[2]. Therefore, the main objectives of this study is to investigate the corrosion properties of the vitamin D loaded TNTs by performing open circuit potential (OCP), electrochemical impedance spectroscope (EIS) and potentiodynamic (PD) testing in phosphate buffer saline (PBS) and bovine calf serum (BCS) solutions. Methods: Ti6Al4V discs were divided into three groups: non-anodized (NA), anodized (A), and vitamin D loaded anodized surfaces (AD). A and AD surfaces were anodized in 0.2-wt% NH4F, 4-vol% H2O, in EG with a constant voltage of 60V for 2 hours. For AD surfaces, 5000 IU of Vitamin D (within recommended dosage by NIH) was loaded inside TNTs using pipetting and centrifuging technique[3]. Finally, corrosion property of each surface was investigated by performing OCP, EIS and PD testing. Results: Figure 1 shows the OCP graphs of NA, A, and AD samples in PBS and BCS. It is observed that the OCP of A and AD samples are significantly high (p<0.05) compared to NA. This suggests that TNTs decorated surface has higher tendency to resist corrosion than non-treated Ti6Al4V surfaces. Figure 2 shows the PD curves for all the samples, which provides information regarding the corrosion current density (Icorr) and passivation current (Ipass). It shows that lower Icorr and Ipass were obtained for A and AD in PBS compared to NA, indicating its ability to resist corrosion. Figure 3 shows the quantitative data of polarization resistance (Rp) and capacitance (C) of the surface. It is observed that significantly high Rp and low C were observed for A and AD surfaces in PBS or BCS solution, which indicates that A and AD surfaces can resist current flow due to electrochemical reaction and it also has less electrochemically active sites for charge transfer that can facilitate corrosion. Discussion: Results from this study show that Vitamin D loaded nanotubes have similar corrosion properties as non-loaded TNTs. Comprehensive analysis from OCP, PD and EIS data suggests that at either at resting or dynamic conditions, anodized surface have a lower tendency to corrode at bone-implant interface due to its thick oxide layer and the ability of the surface to interact with ions in the surrounding environment, thereby forming insulating dielectric film. Additionally, the electrostatic interaction between the negatively charged TNTs and the proteins from the extracellular fluid forms a protective layer on the anodized surface, which explains the high resistance and low capacitance value[4]. Significance: The study highlights two key points in the development of smart TNTs surfaces. First we have shown that a biomimetic surface is possible and second we have demonstrated how these clusters of nanotubes can act as a reservoir for potential drug storage and drug delivery without risking any surface corrosion resistance property loss. This work made use of instrument in the Electron Microscopy Service (Research Resource Center, UIC). Financial support was provided by the Mechanical Engineering Department at MTU. We are grateful to National Science Foundation, DMR Grant # 1350734, NSF award 1359734 and CBET Grant # 1067424, for making some of our characterizations possible.