Vacuum wetting of Ag/TA2 to develop a novel micron porous Ti with significant biocompatibility and antibacterial activity

doi:10.1016/j.jmst.2021.11.045

Abstract

Abstract:

Porous Ti with low modulus, excellent bio-corrosion resistance, biocompatibility, and antibacterial activity is highly pursued as advanced implant materials. In this work, a new approach to prepare micron porous structures on the surface layer of a grade 2 commercially-pure Ti (TA2) was proposed, which utilized a simple vacuum wetting process of pure Ag on the surface of TA2. The microstructure, corrosion resistance, biocompatibility, mechanical properties, antibacterial ability, and formation mechanism of the as-fabricated porous Ti were studied. The results show that the pores (with average pore sizes of 0.5-5 μm) are distributed on the surface layer of the TA2 with a depth of ∼10 μm. In particular, a large number of silver nanoparticles (AgNPs) form which are dispersed on the porous structures. The formation mechanisms of the porous structures and AgNPs were elucidated, suggesting that the volatilization/sublimation of Ag in TA2 is crucial. The porous Ti possesses excellent bio-corrosion resistance, surface wettability, biocompatibility, antibacterial activity, and a relatively low elastic modulus of 40-55 GPa, which may have a promising future in the field of orthopedic implants. This work also provides a novel idea for the development of advanced porous Ti materials for orthopedic-related basic research and biomedical applications.

Key words: Porous titanium, Biomaterials, Vacuum wetting, Porous surface, Antibacterial activity

Guanpeng Liu, Yulong Li, Ming Yan, Jicai Feng, Jian Cao, Min Lei, Quanwen Liu, Xiaowu Hu, Wenqin Wang, Xuewen Li. Vacuum wetting of Ag/TA2 to develop a novel micron porous Ti with significant biocompatibility and antibacterial activity[J]. J. Mater. Sci. Technol., 2022, 116: 180-191.

Figures/Tables 19

Fig. 1. Fabrication of the porous Ti: (a) temperature profiles for the vacuum wetting experiment; macro morphology of the Ag/TA2 specimen (b) before and (c) after the wetting experiment; (d) schematic diagram for preparing the porous structure on the surface of TA2.

Fig. 2. Projection images of the pure Ag wetting over TA2.

Fig. 3. Microstructure characteristics of the porous Ti: (a) and (b) the central area and edge area of the wetting area (porous structure), (c) cross-section of the porous structure, (d) enlarged morphology of the selected area in (a), (e) enlarged morphology of the selected area in (b), (f) enlarged morphology of (c), (g) enlarged morphology of (d), (h) enlarged morphology of (e), and (i) enlarged morphology of the selected area in (f), the inserted images in (e) and (i) are line scan distributions.

Table 1. The EDS analysis associated with Fig. 3.

Empty Cell	EDS results (at.%)
Elements	A	B	C	D	E	F	G
Ti	97.56	95.96	97.41	100	98.44	98.63	100
Ag	2.44	4.04	2.59	0	2.56	1.37	0

Fig. 4. The elemental compositions of the porous structure: (a) EDS analysis of the porous structure, (b) XRD patterns of TA2 substrate and porous structure.

Table 2. Phase transition reaction in the Ag-Ti system.

Phase transition	Type	Temperature ( °C)
(βTi)+Ag(Liquid)⇄TiAg	Peritectic reaction	1020 ± 5
(βTi)+TiAg⇄Ti2Ag	Peritectoid reaction	940 ± 5
(βTi)⇄(αTi)+Ti2Ag	Eutectoid reaction	855 ± 5
Ag(Liquid)⇄TiAg+Ag(Solid)	Eutectic reaction	959 ± 1

Fig. 5. TEM images of the representative areas of the porous structure: (a-c) in different areas, (d) HRTEM image of the AgNPs in (a), (e) the SAED of the black precipitate (AgNPs), (f) the SAED of the matrix (α-Ti), and (g) and (h) STEM images and (i) and (j) EDS mapping of the AgNPs.

Table 3. The weight change of the samples performed in vacuum.

Test 1	Pre-experiment (g)	Post-experiment (g)	Weight-loss (g)
Sample 1 (Ag/TA2)	0.4752	0.4643	0.0109
Sample 2 (Ag/TA2)	0.4707	0.4609	0.0098
Sample 3 (Ag/TA2)	0.4742	0.4623	0.0119
Sample 4 (Ag/TA2)	0.4715	0.4612	0.0103
Sample 5 (TA2)	0.4563	0.4563	0.0000

Table 4. The weight change of samples performed in ultrahigh purity argon.

Test 2	Pre-experiment (g)	Post-experiment (g)	Weight-loss (g)
Sample 6 (Ag/TA2)	0.4644	0.4649	-0.0005
Sample 7 (Ag/TA2)	0.4652	0.4654	-0.0002
Sample 8 (Ag/TA2)	0.4628	0.4635	-0.0007
Sample 9 (Ag/TA2)	0.4680	0.4683	-0.0003
Sample 10 (TA2)	0.4458	0.4460	-0.0002

Fig. 6. Schematic illustration of the formation process of the porous structure.

Fig. 7. Results of electrochemical tests of the porous Ti and TA2 in Hanks’ SBF solution: (a) polarization curves, (b) Nyquist plots, (c) Bode plots of impedance versus frequency, (d) Bode plots of phase angle vs frequency (inserted image means the EC).

Table 5. Corrosion parameters of the porous Ti and TA2 samples.

Sample	E_corr (mV)	I_corr (μA cm^-2)	Corrosion condition	Refs.
Porous Ti	-129	0.163	Hanks’ SBF solution	Present
TA2	-147	0.386	Hanks’ SBF solution	Present
316 L SS	-431	0.853	Hanks’ SBF solution	[58]
NiTi	-99	0.872	Hanks’ SBF solution	[59]
TC4	-178	0.169	Hanks’ SBF solution	[60]

Table 6. Corrosion parameters of the porous Ti and TA2 from the EIS spectra.

Sample	R_p (Ω cm²)	R_s (Ω cm²)	R_t (Ω cm²)	CPE-t (F cm^-2)	CPE-p
Porous Ti	132,672.05	12.05	132,660	1.61 × 10^-5	0.927
TA2	105,505.31	10.31	105,495	2.59 × 10^-4	0.901

Fig. 8. SEM images of the HEPG-2, HUVEC, and MG-63 cells incubated on porous Ti for 2 h: (a) and (b) HEPG-2 cells, (c) and (d) HUVEC cells, (e) and (f) MG-63 cells.

Fig. 9. Optical density measurements for (a) HEPG-2, (b) HUVEC, and (c) MG-63 cells proliferation on the TA2 and porous Ti samples after 24, 72, and 120 h of culture (Note: *** means P < 0.001 compared to TA2).

Fig. 10. The contact angle images of deionized water on (a) porous Ti and (b) TA2.

Fig. 11. (a) Typical nanoindentation load-depth curves and (b) typical relation of modulus and indentation depth for samples of TA2 and porous Ti.

Fig. 12. Release concentration of Ag+ from the porous Ti after specific days of immersion in Hanks’ SBF solution at 37 °C.

Fig. 14. Calculated antibacterial rates of the porous Ti and TA2 samples against S. aureus and E. coli.

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