Titanium and its alloys are reported to be the most suitable material for use as implants in the human body. However, there are reports showing corrosion in the titanium implants due to the bio-environment in the body.
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Surface modification on titanium implants has emerged as an efficient solution for enhancing corrosion resistance. In addition, it enhances other properties necessary for the use as a biomaterial.
Metals are commonly used as implants in the human body; however, they should possess some properties that enable them to function inside the body without side effects.
Metallic biomaterials should have biocompatibility properties, bioadhesion, biofunctionality, and corrosion resistance.
Metallic biomaterials mainly used are stainless steel, cobalt alloys, titanium, and titanium alloys. Titanium and its alloys are the most promising metallic biomaterials that are utilized in various biomedical applications like orthopedic implants, cardiac stent and valve implants, and oral implants.
Advantages of titanium as an implant include biocompatibility, light-weight, corrosion resistance, high strength to weight ratio, non-magnetic features, and low modulus of elasticity.
Straumann, Envista and Osstem Implant (HIOSSEN) are among the various companies that provide titanium-based body implants.
High biocompatibility of titanium is due to the low electrical conductivity, which leads to electrochemical oxidation of titanium and the formation of a thin oxide passivation layer, typically a few nanometers thick. This oxide layer further provides high corrosion resistance to titanium. In addition, the pH value of this oxide layer is the same as that of the human body and has low reactivity with other macromolecules.
Have Titanium Implants Reported Corrosion?
Despite all these properties of titanium, studies are reporting the corrosion of titanium when used as implants. Accumulation of titanium in tissues at the proximity of implant signifying the release and corrosion of metal in in-vivo conditions were reported.
Factors such as body fluid (blood, plasma, and proteins), electrochemical activities of the implant (cathodic or anodic), and interaction with bacteria, bio-molecules, and cells could alter the corrosion resistance and stability of titanium. This could increase corrosion propensity and hasten the destruction of the oxide layer on the titanium implant surface.
An increase in corrosion rate could increase the ion release, which could interact with the surrounding cells affecting the cell metabolic activities. These inflammatory cells could lead to corrosion and further to implant failure.
Corrosion can reduce the life span of implants and consequently can result in re-surgery. In addition, such implant corrosion may lead to a threat to human life.
Modified Titanium Implants With Enhanced Corrosion Resistance:
Surface modification of titanium implants for enhancing the corrosion resistance and related properties of biomaterials has proved to be the most useful and viable strategy.
Titanium nitride surface layers over titanium implant were studied as wear-resistant and corrosion-resistant surface modification. Titanium nitride phases had shown suppressing ion release and stabilizing the growth of titanium oxide layer on the surface of titanium.
Plasma immersion ion implantation was reported to be another technique through which ions of nitrogen, carbon, and oxygen could be implanted on the titanium surface to obtain desired properties. This modified surface layer was further treated with another layer for better results.
Ultrafine nanoparticles have shown selective oxidation that creates a defense mechanism to corrosion and have shown greater adhesion to the surface of biomaterials.
Studies on the surface modification of titanium substrates through surface treatment methods creating nanorough surfaces utilizing titanium oxide, aluminum oxide, and hydroxyapatite, were reported. Other surface modifying nanostructures, such as nanoporous membranes and nanofibers, were also studied.
Zinc coatings are widely used in biomedical applications due to their improved osteoblastic differentiation. Modifying the surface of titanium with zinc nanowires has been reported to show antioxidant and anti-inflammatory properties. In addition, it showed reduced corrosion susceptibility of titanium in the oxidizing microenvironment.
Nanoscale zinc oxide particles had reported properties like antimicrobial and low toxicity. In the study, antibacterial properties of zinc oxide nanoparticles were exhibited due to the release of Zn2+ ions and reactive oxygen species.
The appropriate amount of zinc on the surface of biomaterials has been reported to create a good environment for cell adhesion, proliferation, mineralization, and many more.
Studies have reported titanium implants can be modified with nano zinc oxide nanoparticle coatings through various methods, such as electrodeposition, atomic layer deposition, sol-gel method, magnetron sputtering, laser deposition, hydrothermal method, and electrohydrodynamic spraying.
Future Perspective of Modified Titanium Implants:
Surface-modified titanium through various materials has shown corrosion resistance and increased biocompatibility. However, it is requisite to construct sophisticated microenvironment models that mimic the human body, to study biochemical mechanisms happening after implantation under immune response.
This will further help develop multifunctional nanomaterials for superior metallic biomaterials, which could show enhanced corrosion resistance, improved osseointegration efficiency, and biocompatibility.
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References and Further Reading:
Sidambe, A.T. (2014) Biocompatibility of advanced manufactured titanium implants—A review. Materials, 7(12), pp.8168-8188. Available at: https://doi.org/10.3390/ma7128168.
Sharan, J., Lale, S.V., Koul, V., Mishra, M. and Kharbanda, O.P. (2015) An Overview of Surface Modifications of Titanium and its Alloys for Biomedical Applications. Trends in Biomaterials & Artificial Organs, 29(2). Available at: https://biomaterials.org.in/tibao/index.php/tibao/article/view/133.
Aziz-Kerrzo, M., Conroy, K.G., Fenelon, A.M., Farrell, S.T. and Breslin, C.B. (2001) Electrochemical studies on the stability and corrosion resistance of titanium-based implant materials. Biomaterials, 22(12), pp.1531-1539. https://www.sciencedirect.com/science/article/abs/pii/S0142961200003094?via%3Dihub
Zhu, W.Q., Shao, S.Y., Xu, L.N., Chen, W.Q., Yu, X.Y., Tang, K.M., Tang, Z.H., Zhang, F.M. and Qiu, J. (2019) Enhanced corrosion resistance of zinc-containing nanowires-modified titanium surface under exposure to oxidizing microenvironment. Journal of nanobiotechnology, 17(1), pp.1-18. Available at: https://doi.org/10.1186/s12951-019-0488-9.
Wang, Z., Wang, X., Wang, Y., Zhu, Y., Liu, X. and Zhou, Q. (2021) NanoZnO-modified titanium implants for enhanced anti-bacterial activity, osteogenesis and corrosion resistance. Journal of Nanobiotechnology, 19(1), pp.1-23. https://jnanobiotechnology.biomedcentral.com/articles/10.1186/s12951-021-01099-6
Mohammed, M.T., Khan, Z.A. and Siddiquee, A.N. (2014) Surface modifications of titanium materials for developing corrosion behavior in human body environment: a review. Procedia Materials Science, 6, pp.1610-1618. Available at: https://doi.org/10.1016/j.mspro.2014.07.144.