Short communicationInvestigation of morphology and bioactive properties of composite coating of HA/vinyl acetate on pure titanium
Introduction
Metals still account for a substantial percentage of clinically used materials and for many medical applications. They have the attributes of strength, stiffness, toughness and impact resistance properties, that are particularly important for load bearing applications, such as total joint replacements. Major implant materials used in medical and dental applications include commercially pure titanium and its alloys. However, after their application, a bond with living bone often does not develop or the integration of the implants with bone tissue takes generally several months. Hence, there is a growing interest in shortening the process toward osseointegration, and reducing the surgical restrictions. In the past three decades, research in this field has been oriented towards coating titanium implants with hydroxyapatite. Many coating procedures have been documented, but all have shortcomings.
Calcium phosphate ceramics have been received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several forms of Cap, synthetic hydroxyapatite [Ca10(PO4)5(OH)2, hereafter HA], a major inorganic component of natural bone, is particularly attractive. HA is recognized as osteoconductive and able to accelerate bone in growth and attachment to the surface of implant during the early stages after implantation. Furthermore, the fixation and lifetime of the implant are improved. However, the mechanical strength is too poor to use in load-bearing prostheses were investigated to maintain biocompatibility and to improve mechanical properties [1], [2], [3].
Electrochemical methods of calcium phosphate coating for biomedical applications have been investigated since 1990s. Electrochemical deposition of HA coating can be conducted at room temperature. Thus homogeneity of chemistry and phase can be readily performed. Since the deposition of HA is nonlinear in nature, HA can be deposited on the internal surface of porous metal substrates. The coating morphology can be controlled in electrochemical deposition due to the easy control of the deposition rate by varying the electrochemical potential, current density, electrolyte concentration and temperature. The calcium phosphate coating by the electrochemical technique has been shown to exhibit higher bioactivity in vivo experiments. The morphology of the deposited HA can change from needle to granule type. There are two main techniques used for electrochemical: (1) anodic oxidation of metal surface in electrolyte containing calcium (Ca) and phosphorus (P) plus high-pressure steam treatment to produce Ca/P precipitation; (2) direct deposition of calcium phosphate on a metal cathode. The second method is simpler and more widely studied [4], [5], [6], [7], [8], [9], [10].
The present work is aimed to improving the bioactive properties of HA coating by modifying the electrochemical processing. This is done by adding variable amount of vinyl acetate in the electrolyte, so that the HA and the biocompatible polymer could be co-deposited on the titanium substrate. Vinyl acetate polymer has used as a dental material due to its good biocompatibility and chemical stability. It is expected that a synergistic effect of co-deposition of HA coating and vinyl acetate polymer might exhibit improved crystallization of HA coating, with better bioactivity [11], [12], [13].
Section snippets
Solution preparation and electro-deposition
The HA coating were obtained by cathodic deposition method in electrochemical processing; 30 mm × 20 mm × 3 mm plates of Ti were used as the cathode, that on them HA was deposited. The Ti plates were polished using abrasive paper of 600 grits, degreased with methanol and rinsed with deionized water before the deposition processing. The electrolyte was an aqueous solution containing 0.0042 mM of Ca(NO3)2·4H2O, 0.0025 mM of NH4H2PO4, with 0.006, 0.01, 0.014, 0.018, 0.022 and 0.026 vol.% of vinyl acetate.
Results and discussion
The electrodeposited biomaterial layers on the both sides of the Ti plate were obtained after electrochemical processing for 1 h. The average thickness of HA coating was around 20 μm. The XRD analysis indicated, that HA was the main phase. Fig. 1a–d shows the XRD spectra of the deposited layers with variable amount of the vinyl acetate. There was no evidence that vinyl acetate can change chemical composition of the calcium phosphate during the deposition process. Table 1, Table 2 show the
Conclusion
Electrochemical method was developed for co-depositing HA/vinyl acetate polymer composite coating on titanium surface. The HA/polymer composite coating has not only a better crystallization, but also a better bioactivity, due to a remarkable change on the surface morphology, by increasing amount of vinyl acetate in the composite bio-ceramic coating. The present work showed that by increasing the amount of vinyl acetate in the electrolyte, flower-type pattern grow is increased. On the other
Acknowledgments
One of the authors, Mardali Yousefpour, gratefully thanks Sharif University of Technology in Iran and National Engineering Research Center in Biomaterials at Sichuan University in China for the research support.
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