Full Length ArticleIn-vitro biocompatibility and corrosion resistance of electrochemically assembled PPy/TNTA hybrid material for biomedical applications
Graphical abstract
Introduction
Over the past decades, there is an increasing demand for biomedical implants and the researchers have been trying to develop a appropriate bioactive implant material for use in the human body [1], [2]. Titanium and its alloys has become the material of choice in medical applications due to unique combination of favorable material properties like strength, biocompatibility and corrosion resistance compared to other metallic implants [3], [4]. However, being bioinert in nature, it cannot bond directly to living bone after implantation. Inorder to solve the above stated issue, modifying the surface to improve the bio performance of titanium implants is essential [5]. Recent researches in this field have highlighted the importance of altering the surface morphology to nanoscale by the formation of TiO2 nanotubes to better mimic the surface features of natural bone in the nanoscale regime and to favor a positive cellular interaction with cells [6], [7], [8].
Polypyrrole (PPy), one of the promising conducting polymers has been highly investigated for biomedical applications because of its significant features like conductivity, ease of preparation, good biocompatibility and chemical stability [9], [10], [11]. PPy can be used for the development of efficient biomimetic systems such as artificial muscles [12], drug delivery [13], scaffold material for nerve regeneration [14] and compatible with wide range of cell types In-vitro [15] and in vivo [16], [17]. PPy is being employed as a biocompatible and electroactive polymeric substrate for the manipulation of cell growth, adhesion and proliferation of numerous tissues like bone, skin, cartilage etc due to its capability to electronically control a wide range of physical and chemical properties [18]. Despite all the advantages, PPy has some inherent shortcomings such as poor mechanical strength, processability, which hinders its application in biomedicine. One of the known drawbacks of the polypyrrole is its poor adhesion to oxidizable metals (Al, Fe, Zn, Ti) [2]. Development of hybrid nanomaterial by combining inorganic and organic components in to a single material has been one of the recent approaches in attempting to overcome the above limitations.
Hybrid assemblies with ordered structure, distinct morphologies and good electrical contact with substrate can be developed by infiltrating the polypyrrole in to TiO2 nanotube framework. The properties of both oxide semiconductor and the organic counterpart can be combined through the formation of hybrid structures. Among the different approaches reported such as chemical [19] thermal [20] and UV photopolymerization [21] to develop homogenous hybrid materials, electropolymerization is a particular versatile method to deposit the conducting polymer as it can be directly electrodeposited on the inorganic nanostructure which acts as the working electrode. The fundamental understanding of the site selective filling of the nanotubes with polypyrrole using pulse current approach was reported by Kowalski et al. [22]. Ngaboyamahina et al. [23] reported the deposition of polypyrrole into titanium nanotube arrays in dark using lithium perchlorate electrolyte, signifying the influence of back ground salt in the rate of deposition of polypyrrole. However, controlled experimental conditions are required for the effective and homogenous electrodeposition of conducting polymer into TiO2 nanostructures. The electrochemically synthesized NTA/PPy hybrid system has been used for solar energy [24] and super capacitor [25] applications as revealed from literature. Despite the fact that titania nanostructures and polypyrrole were distinctly used for many implant applications, to the best of our knowledge, the use of polypyrrole/titania nanotube arrays (PPy/TNTA) hybrid system to modify the bioimplants in terms of electrochemical stability and biocompatibility is rather scarce.
Hence, the main goal of the present study is to fabricate PPy/TNTA hybrid material for biomedical application. Indeed, we demonstrate normal pulse voltammetry technique by varying the pulse potential to achieve a homogenous deposition of polypyrrole on titania nanotube frame work. The phase composition, morphology, surface roughness and wettability of the hybrid material were studied. Further the paper mainly extends the investigation to focus on the analysis of the electrochemical corrosion behavior of PPy/TNTA using potentiodynamic polarization and electrochemical impedance spectroscopy studies. We also evaluated the biocompatibility performance of PPy/TNTA on MG63 osteoblast cells via In-vitro cell culture studies.
Section snippets
Materials
Commercially pure titanium (Cp-Ti) of thickness (2 mm) was obtained from Ti Anode Fabricators, Chennai. Pyrrole (monomer), lithium perchlorate, glycerol and all other chemicals used in the present study were purchased from Sigma Aldrich chemical company. The pyrrole monomer was distilled before use and all other chemicals were used without any further treatment. Double distilled water was used to make all the solutions.
Fabrication of titania nanotube arrays (TNTA)
Prior to anodization, titanium sheets (1.5 × 2 × 0.2 cm3) were cut and
Preparation of PPy/TNTA hybrid
PPy/TNTA hybrid was prepared by normal pulse voltammetry electrodeposition process. After a series of optimization experiments, electrolyte solution containing 0.2 M LiClO4 and 0.1 M pyrrole were chosen for the deposition process. Fig. 1(a) shows the applied potential curve in the normal pulse voltammetry electrodeposition process. The pulse width was 0.06 s and the pulse period was controlled at 4 s and 6 s respectively to benefit pyrrole monomer deposition. The current curve obtained during
Conclusions
Fabrication of PPy/TNTA hybrid material was successfully achieved by normal pulse voltammetry electrodeposition method. The morphology, chemical identity and interaction between PPy and TNTA were studied using HR-SEM, XPS, ATR-FTIR and Raman spectroscopy studies respectively. TNTA retained the nanotubular morphology even after the deposition of polypyrrole as evidenced from the HR-SEM images. Controlled filling of PPy initially in to the spaces between the nanotubes at pulse potential of 4 s
Acknowledgement
One of the authors Simi.V.S is thankful to Department of Science and Technology (DST), New Delhi, India for financial assistance under women scientist scheme (WOS-A) (Ref.N0: SR/WOS-A/CS-93/2012(G) Dated: 20.09.2013). The Instrumentation facilities provided by DST-FIST and UGC-DRS to Department of Chemistry, Anna University, Chennai, India are gratefully acknowledged.
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