Comparative Study of the Effects of Nano ZnO and CuO on the Biodegradation, Biocompatibility, and Antibacterial Properties of Micro-arc Oxidation Coating of Magnesium Alloy

doi:10.1007/s40195-023-01627-3

Abstract

Abstract:

This research systematically examined the degradation, antibacterial effects, and biocompatibility of micro-arc oxidation (MAO) coatings with nano CuO and ZnO on extruded Mg alloys. Both copper (Cu) and Zinc (Zn) possess antibacterial properties. The findings demonstrated that adding ZnO will appreciably reduce the degradation rate of MAO-coating alloy due to the self-sealing micro holes. CuO + MAO coating exhibited excellent antibacterial performance, with an antibacterial rate of over 90% within 6 h co-cultured with Staphylococcus aureus. Similarly, the antibacterial rate of ZnO + MAO coating reached 90% after 12 h co-culture. Cytotoxicity test using MG63 cell indicated that the incorporation of CuO and ZnO did not notably affect the cell viability rate of the coating. Moreover, after 14 days of culture, the CuO + MAO and ZnO + MAO coated samples exhibited higher alkaline phosphatase (ALP) activity than the MAO-coated and uncoated samples, suggesting favorable osteogenic properties.

Key words: Copper oxide, Zinc oxide, Micro-arc oxidation (MAO) coating, Corrosion behavior, Antibacterial characteristics

Ying Shen, Xianfeng Shan, Iniobong P. Etim, Muhammad Ali Siddiqui, Yang Yang, Zewen Shi, Xuping Su, Junxiu Chen. Comparative Study of the Effects of Nano ZnO and CuO on the Biodegradation, Biocompatibility, and Antibacterial Properties of Micro-arc Oxidation Coating of Magnesium Alloy[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(2): 242-254.

Figures/Tables 13

Table 1 Composition of the electrolyte fabricating MAO coatings

Coatings	Ca(OH)₂ (g/L)	(NaPO₃)₆ (g/L)	KF (g/L)	Nano-CuO (g/L)	Nano-ZnO (g/L)
MAO	1.2	4.0	8.0	-	-
CuO + MAO	1.2	4.0	8.0	1.0	-
ZnO + MAO	1.2	4.0	8.0	-	1.0

Fig. 1 Microstructure of coatings: a1-c1 cross section; a2-c2 surface morphology; a3-c3 surface porosity

Table 2 EDS analysis of the areas marked in Fig. 1

Samples	Position	Composition (at.%)
Samples	Position	O	Mg	F	P	Ca	Cu	Zn
MAO coating	A	46.15	25.61	13.08	11.28	3.87	-	-
	Pore opening	46.41	21.21	15.66	12.38	4.35	-	-
	Pore sealing	43.29	21.05	22.00	9.50	4.16	-	-
CuO + MAO coating	B	43.53	24.44	14.89	12.11	4.95	0.08	-
	Pore opening	31.02	25.36	9.42	17.49	16.72	-	-
	Pore sealing	44.4	23.68	22.47	6.98	2.29	0.18	-
ZnO + MAO coating	C	43.21	31.99	15.56	8.14	0.76	-	0.35
	Pore opening	38.66	28.18	7.77	18.38	2.02	-	4.99
	Pore sealing	42.12	31.43	13.53	10.32	0.69	-	1.91

Fig. 2 XRD patterns of the coatings: a MAO coating, b CuO + MAO coating, c ZnO + MAO coating

Fig. 3 Electrochemical tests of potentiodynamic polarization and impedance curves: a potentiodynamic polarization curves, b Nyquist curves, c Bode curves, d Bode phase angle curves, e equivalent circuit of MAO coated alloy and CuO + MAO coated alloy, f equivalent circuit of ZnO + MAO coated alloy

Table 3 Tafel fitting results based on potentiodynamic polarization tests in Hank's solution

Samples	i_corr (µA/cm²)	E_corr (V)	Corrosion rate (mm/y)
MAO coated	0.44 ± 0.03	− 1.55 ± 0.02	0.010 ± 0.0001
CuO + MAO coated	0.42 ± 0.04	− 1.53 ± 0.03	0.009 ± 0.0009
ZnO + MAO coated	0.19 ± 0.02	− 1.50 ± 0.02	0.004 ± 0.0004

Table 4 Fitting results of different samples immersed in Hank's solution

Samples	R_s (Ω cm²)	CPE₁		R₁ (Ω cm²)	CPE₂		R₂ (Ω cm²)	R₃ (Ω cm²)	L (H cm⁻²)
Samples	R_s (Ω cm²)	Y₀₁ (μΩ⁻¹ cm⁻² s⁻¹)	n₁	R₁ (Ω cm²)	Y₀₂ (μΩ⁻¹ cm⁻² s⁻¹)	n₂	R₂ (Ω cm²)	R₃ (Ω cm²)	L (H cm⁻²)
MAO coated	24.91	4.75 × 10^-8	0.90	2317	3.64 × 10^-6	0.43	4.75 × 10⁴	2.93 × 10⁵	8.35 × 10⁴
CuO + MAO coated	19.00	4.99 × 10^-7	0.73	8.14 × 10⁴	6.17 × 10^-7	0.70	1.49 × 10⁵	1.97 × 10⁵	1.13 × 10⁷
ZnO + MAO coated	17.67	1.55 × 10^-8	0.99	1011	4.46 × 10^-7	0.70	3.99 × 10⁵	-	-

Fig. 4 pH values of Hank's solution during the sample immersion period

Fig. 5 Corrosion morphologies of the samples after 14 days of immersion in Hank's solution: a1-c1 micro-cross-sectional morphologies of the coated samples; a2-c2 micro-surface morphologies of the coated samples; a3-c3 macro-surface morphologies of the coated samples

Table 5 EDS analysis of the areas marked in Fig. 5

Samples	Position	Composition (at.%)
Samples	Position	O	Mg	F	P	Ca	Cu	Zn
MAO coating	A	55.19	23.11	3.46	14.30	3.95	-	-
CuO + MAO coating	B	49.06	25.44	9.39	13.85	2.25	-	-
ZnO + MAO coating	C	51.45	25.12	6.56	13.29	3.15	-	0.43

Fig. 6 Antibacterial tests of a antibacterial effects of materials co-cultured with S. aureus for 6, 12, and 24 h, respectively, b the content of Zn and Cu ions in Hank’s solution for 6, 12, and 24 h, respectively. c S. aureus concentration in the bacterial solution co-cultured with different samples, and d antibacterial rates of different samples against S. aureus

Fig. 7 SEM morphologies of S. aureus on surfaces of different samples after co-culture for 24 h with a MAO-coated alloy, b CuO + MAO coated alloy, and c ZnO + MAO-coated alloy

Fig. 8 a Cell viability of cells (MC3T3-E1) in different extracts after 1, 3, and 5 d, b relative ALP activity of cells after being cultured in the extracts of different samples for 7 and 14 d. (*p < 0.05)

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