Date Published: May 22, 2019
Publisher: Public Library of Science
Author(s): Murali Krishna Duvvuru, Weiguo Han, Prantik Roy Chowdhury, Sahar Vahabzadeh, Federico Sciammarella, Sherine F. Elsawa, Sakamuri V. Reddy.
Inflammation and implant loosening are major concerns when using titanium implants for hard tissue engineering applications. Surface modification is one of the promising tools to enhance tissue-material integration in metallic implants. Here, we used anodization technique to modify the surface of commercially pure titanium (CP-Ti) and titanium alloy (Ti-6Al-4V) samples. Our results show that electrolyte composition, anodization time and voltage dictated the formation of well-organized nanotubes. Although electrolyte containing HF in water resulted in nanotube formation on Ti, the presence of NH4F and ethylene glycol was necessary for successful nanotube formation on Ti-6Al-4V. Upon examination of the interaction of bone marrow stromal cells (BMSCs) with the modified samples, we found that Ti-6Al-4V without nanotubes induced cell proliferation and cluster of differentiation 40 ligand (CD40L) expression which facilitates B-cell activation to promote early bone healing. However, the expression of glioma associated protein 2 (GLI2), which regulates CD40L, was reduced in Ti-6Al-4V and the presence of nanotubes further reduced its expression. The inflammatory cytokine interleukin-6 (IL-6) expression was reduced by nanotube presence on Ti. These results suggest that Ti-6Al-4V with nanotubes may be suitable implants because they have no effect on BMSC growth and inflammation.
Commercially pure titanium (CP-Ti) and titanium alloy (Ti-6Al-4V) are widely used as dental and orthopedic implants due to their biocompatibility, excellent corrosion resistance and desired mechanical properties. This includes properties such as low Young’s modulus, low density and fatigue resistance [1–3]. However, the formation of a fibrous capsule around titanium implants and the resultant implant loosening can cause severe pain for patients, which often requires revision surgery . Surface modification techniques such as applying an osteoconductive coating, alkali treatment, acidic treatment, and electrochemical anodization are promising tools to enhance osseointegration of Ti implants . Among the various techniques, introducing TiO2 nanotubes on the surface of Ti through anodization has gained attention as it is a simple, cost efficient and well controlled methodology. However, parameters such as electrolyte composition, voltage and the duration of anodization have been shown to alter the morphology of the surface [6,7]. In the current study, we used five different conditions to investigate and compare the effects of substrate composition and anodization parameters on successful formation of nanotubes on both CP-Ti and Ti-6Al-4V [8,9]. We hypothesized that different conditions are needed to achieve well-formed nanotubes on CP-Ti and Ti-6Al-4V.
TiO2 nanotubes are of great interest due to their excellent physical, mechanical and biological properties. Previous studies have reported that nanotubes enhance the protein adsorption and osteoblast cell attachment which improves bioactivity [23,24]. In this study, we fabricated nanotubes on the surface of both CP-Ti and Ti-6Al-4V using experimental different conditions. These conditions were selected based on previous work for different types of titanium alloys [8,9]. We found that formation of nanotubes depends on both anodization parameters and substrate composition. This is in line with the literature where formation of nanotubes was confirmed on IMI834 titanium alloy using H3PO4+HF electrolyte, whereas no nanotube was found on CP-Ti and Ti-6Al-4V substrates using the same anodization conditions, showing the dependency of the successful anodization on phase composition of Ti and its alloys . Nanotubes formed by anodization are usually referred to as TiO2 nanotubes. However, pure TiO2 nanotubes are formed only on CP-Ti while the presence of Al and V in Ti-6Al-4V results in formation of Ti-Al-V-O nanotubes. High amounts of Al decrease the dissolution rate, while the presence of V increases the dissolution rate which affect nanotube formation . Similar to Al and V, increase in Zr content in Ti-alloy increases interspace between TiO2 nanotubes . However, regardless of Ti composition, the presence of fluoride ions appears crucial for the growth of TiO2 nanotubes, as F- helps in the chemical dissolution of the oxide layer. In addition to F-, water content and the viscosity of ethylene glycol (EG) alter nanotube formation as they alter the rate of oxidation and diffusion of ions in the electrolyte, respectively [27,28].