In-Vitro and in-Vivo Responses of New Promising Surface Modification of Ti6Al4V Implants by TiTaNb Multiple Principal Element Coating
先進鈦鉭鈮多元合金薄膜對Ti6Al4V植入物表面改質之體內外測試分析
Student thesis: Doctoral Thesis
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Award date | 4 Jul 2023 |
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Permanent Link | https://scholars.cityu.edu.hk/en/theses/theses(70e21ff0-5b88-4c46-a9b7-0abb5bc80011).html |
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Abstract
Ti-6Al-4V (in wt%) is one of the common orthopedic implants due to the high strength-to-weight ratio, average corrosion resistance and lightweight characteristic. However, despite the widespread usage of Ti6Al4V in orthopedics, some reports pointed out that the metallic wear debris and the released Al and V ions may induce the potential neurotoxic effects like Alzheimer's disease, neuropathy, and osteomalacia. In addition, the human body fluid is full of chloride ions, which are corrosive and can prompt dissolution of implants, leading to the sharp and narrow pits produced on surfaces that make the implants weaker and damaged. From the prospective of long-term implantation in human body, the corrosion resistance of Ti6Al4V is still not highly satisfactory. Furthermore, Ti6Al4V is weak in inducing osteointegration due to its inert biological properties. For the above reasons, surface modification for Ti6Al4V is a method to eliminate the health concerns and improve the innate bio-inert property. Surface modification can also enhance corrosion and wear resistance of Ti6Al4V to achieve the goal of long-term implantation. Therefore, we prepare the Ti-Ta-Nb multiple-principal-element bioactive films by sputtering as the potential candidates to modify the physical and chemical properties of Ti6Al4V. All these elements exhibit great biocompatibility in human body and the alloying of Ti with Ta and Nb can stabilize the passive layer and enhance the corrosion resistance. Besides, among these elements, Ta is a bioactive metal with excellent osteogenic properties and known as one of the most excellent bio-corrosion resistant elements owing to the formation of dense Ta2O5 passive layer. It follows that we investigate in this thesis work the influence of bioactive element Ta content from 25, 33, to 50 at% in this system by a series of in-vitro and in-vivo biocompatibility measurements.
Firstly, the mechanical properties and wear resistance are examined in the beginning. We then explore the corrosion behavior of Ti-Ta-Nb series films by electrochemical measurements. The Ti-Ta-Nb system shows significantly improved corrosion resistance compared to Ti6Al4V in the modified simulated body fluid (m-SBF). In addition, from the polarization curve and EIS results, Ta50 has the highest corrosion resistance among these films, following TiTaNb and Ti50. Moreover, passivation is another important factor related to the corrosion properties. The passivation mechanism and passive layer analyses are extensively explored and discussed in this study.
Secondly, the in-vitro biological responses are analyzed by four categories: cell viability, cell attachment, cell proliferation and cell differentiation. Due to the addition of bioactive element, Ta, the results show that the biological properties of Ti6Al4V can be improved by Ti-Ta-Nb coating films, and among these films, Ta50 has the highest active cell–surface interaction level to show the best biological properties. Generally speaking, the highly hydrophilic surfaces are more desirable for cells to adhere. However, some studies indicate the higher hydrophilic surface does not always correspond to higher cell adhesion, the cell might be favored on moderate hydrophilic biomaterial surfaces. In our study, the D1 cells which we use in the experiments prefer to attach on surface with a water contact angle about 60°.
Finally, the Ti6Al4V base alloy and the Ti6Al4V substrate coated with 3 different Ti-Ta-Nb films in composition are implanted in the rabbits’ tibias for 3, 6 and 9 weeks. The order of calculated in-vivo response value for bone matrix/area and morphogenetic protein-2 (BMP-2) is all Ta50 > TiTaNb > Ti50 > Ti6Al4V. These results support the in-vitro tests and prove that Ta could significantly facilitate bone-tissue regeneration.
Given these points, this thesis study has explored the brand new sputtered bioactive Ti-Ta-Nb system for feasible orthopedic implantation. The Ta50 film is found to possess great potential as the promising choice for surface modification materials.
Firstly, the mechanical properties and wear resistance are examined in the beginning. We then explore the corrosion behavior of Ti-Ta-Nb series films by electrochemical measurements. The Ti-Ta-Nb system shows significantly improved corrosion resistance compared to Ti6Al4V in the modified simulated body fluid (m-SBF). In addition, from the polarization curve and EIS results, Ta50 has the highest corrosion resistance among these films, following TiTaNb and Ti50. Moreover, passivation is another important factor related to the corrosion properties. The passivation mechanism and passive layer analyses are extensively explored and discussed in this study.
Secondly, the in-vitro biological responses are analyzed by four categories: cell viability, cell attachment, cell proliferation and cell differentiation. Due to the addition of bioactive element, Ta, the results show that the biological properties of Ti6Al4V can be improved by Ti-Ta-Nb coating films, and among these films, Ta50 has the highest active cell–surface interaction level to show the best biological properties. Generally speaking, the highly hydrophilic surfaces are more desirable for cells to adhere. However, some studies indicate the higher hydrophilic surface does not always correspond to higher cell adhesion, the cell might be favored on moderate hydrophilic biomaterial surfaces. In our study, the D1 cells which we use in the experiments prefer to attach on surface with a water contact angle about 60°.
Finally, the Ti6Al4V base alloy and the Ti6Al4V substrate coated with 3 different Ti-Ta-Nb films in composition are implanted in the rabbits’ tibias for 3, 6 and 9 weeks. The order of calculated in-vivo response value for bone matrix/area and morphogenetic protein-2 (BMP-2) is all Ta50 > TiTaNb > Ti50 > Ti6Al4V. These results support the in-vitro tests and prove that Ta could significantly facilitate bone-tissue regeneration.
Given these points, this thesis study has explored the brand new sputtered bioactive Ti-Ta-Nb system for feasible orthopedic implantation. The Ta50 film is found to possess great potential as the promising choice for surface modification materials.