A novel biomedical titanium alloy with high antibacterial property and low elastic modulus

doi:10.1016/j.jmst.2021.01.015

Abstract

Abstract:

β-type titanium alloys have attracted much attention as implant materials because of their low elastic modulus and high strength, which is closer to human bones and can avoid the problem of stress fielding and extend the lifetime of prosthetics. However, other issues, such as the infection or inflammation postimplantation, still trouble the titanium alloy's clinical application. In this paper, we developed a novel near β-titanium alloy (Ti-13Nb-13Zr-13Ag, TNZA) with low elastic modulus and strong antibacterial ability by the addition of Ag element followed by proper microstructure controlling, which could reduce the stress shielding and bacterial infections simultaneously. The microstructure, mechanical properties, corrosion resistance, antibacterial properties and cell toxicity were studied using SEM, electrochemical testing, mechanical test and cell tests. The results have demonstrated that TNZA alloy exhibited an elastic modulus of 75-87 GPa and a strong antibacterial ability (up to 98 % reduction) and good biocompatibility. Moreover, it was also shown that this alloy's corrosion resistance was better than that of Ti-13Nb-13Zr. All the results suggested that Ti-13Nb-13Zr-13Ag might be a competitive biomedical titanium alloy.

Key words: Low Young’s modulus, Antibacterial property, Titanium alloy, Compatibility, Antibacterial titanium alloy

Diangeng Cai, Xiaotong Zhao, Lei Yang, Renxian Wang, Gaowu Qin, Da-fu Chen, Erlin Zhang. A novel biomedical titanium alloy with high antibacterial property and low elastic modulus[J]. J. Mater. Sci. Technol., 2021, 81: 13-25.

Figures/Tables 16

Table 1 Chemical composition of TNZA alloy tested by EDS (wt.%).

Nb	Zr	Ag	Ti
12.72	12.37	12.50	Balanced

Fig. 1. XRD patterns of TNZA(T4, T6-2h, T6-4h, T6-6h).

Fig. 2. Optical microstructures of TNZA: (a) T4, (b) T6-2h, (c) T6-4h, (d) T6-6h.

Fig. 3. SEM microstructures (backscattered electron mode) of TNZA: (a) T4, (b) T6-2h, (c) T6-4h, (d) T6-6h.

Table 2 The results of EDS analysis.

Materials	EDS position	Elements (wt.%)
Materials	EDS position	Ti	Nb	Zr	Ag
T4	Point A	60.59	13.26	13.63	12.52
T6-2h	Point B	59.74	7.98	7.21	25.07
T6-2h	Point C	59.81	13.55	13.83	12.81
T6-4h	Point D	62.35	12.35	13.07	12.23
T6-4h	Point E	58.7	6.56	7.87	26.87
T6-6h	Point F	60.86	12.45	13.43	13.26
T6-6h	Point G	39.81	8.44	6.24	45.51

Fig. 4. TEM images of TNZA: (a-d) show the microstructures of T4, T6-2h, T6-4h, and T6-6h samples with SAD, (e) and (f) the high-solution TEM microstructures of T6-4h sample.

Fig. 5. STEM and element mappings of T6-4h specimen.

Fig. 6. Microhardness and elastic modules of TNZA alloys with different heat treatments.

Fig. 7. Electrochemical characteristics and equivalent circuits for modeling impedance parameters of TNZA alloys: (a) Open-circuit potential (OCP), (b) Tafel curves, (c) Nyquist plots and equivalent circuit (Rs, CPE, Rp), (d) Bode phase plots.

Table 3 Electrochemical data determined from electrochemical experiments (the cp-Ti and Ti-6Al-4 V data listed as well [29,30]).

Materials	E_ocp (mV)	i_corr (μA/cm²)	E_corr (mV)	R_s (Ω cm²)	CPE (μF/cm²)	n	R_p (10⁵ Ω cm²)
T4	-74.5 ± 8.6	0.201 ± 0.011	-153.62 ± 19.34	58.36 ± 8.72	686.8 ± 20.32	0.801 ± 0.012	7.614 ± 0.81
T6-2h	-105.2 ± 12.2	0.636 ± 0.045	-227.17 ± 23.12	59.76 ± 7.33	731.9 ± 23.56	0.825 ± 0.014	8.395 ± 0.056
T6-4h	-118.4 ± 11.4	0.133 ± 0.032	-262.53 ± 21.56	58.65 ± 7.58	241.3 ± 12.36	0.902 ± 0.023	11.902 ± 0.67
T6-6h	-100.6 ± 10.0	0.824 ± 0.046	-128.98 ± 22.28	60.19 ± 9.23	552.4 ± 19.92	0.836 ± 0.036	4.844 ± 0.89
Cp-Ti	-135.0	0.260	-157
Ti-6Al-4V	-	0.032	-265

Fig. 8. Ag ion release concentration from TNZA alloys after 1 day, 3 days and 7 days immersion.

Fig. 9. Typical bacteria colonies on cp-Ti and TNZA with different heat treatments alloys and antibacterial rates: (a) cp-Ti, (b) T4, (c) T6-2h, (d)T6-4h, (e) T6-6h, (f) antibacterial rates of TNZA alloys (p < 0.05).

Fig. 10. Dead and live bacteria staining results on cp-Ti and TNZA samples with different heat treatments: (a) cp-Ti, (b) T4, (c) T6-2h, (d) T6-4h, (e) T6-6h.

Fig. 11. Survival rates of MC3T3-E1 with samples' 3-day-soaking solution after 1 day, 3 days and 7 days culture: (a) the OD value and (b) the survival rates of cells cultured for different time.

Fig. 12. Cell morphologies after 48h incubation on cp-Ti and TNZA samples: (a) cp-Ti, (b) T4, (c) T6-2h, (d) T6-4h, (e) T6-6h.

Fig. 13. (Bo)-(Md) map of titanium alloys [33].

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