In vitro and in vivo biodegradation and biocompatibility of an MMT/BSA composite coating upon magnesium alloy AZ31

doi:10.1016/j.jmst.2020.02.006

Abstract

Abstract:

The performance of biodegradable magnesium alloy requires special attention to rapid degradation and poor biocompatibility, which can cause the implant to fail. Here, a sodium montmorillonite (MMT)/bovine serum albumin (BSA) composite coating was prepared upon magnesium alloy AZ31 via hydrothermal synthesis, followed by dip coating. We evaluated the surface characterization and corrosion behavior in vitro, and the biocompatibility in vitro and in vivo. Biodegradation progress of the MMT-BSA coated Mg pieces was examined through hydrogen evolution, immersion tests, and electrochemical measurements in Hank’s solution. In vitro biocompatibility studies were evaluated via hemolysis tests, dynamic cruor time tests, platelet adhesion, MTT testing and live-dead stain of osteoblast cells (MC3T3-E1). It was found that the MMT-BSA coating had good corrosion resistance and a marked improvement in biocompatibility in comparison to bare Mg alloy AZ31. in vivo studies were carried out in rat model and the degradation was characterized by computed tomography scans. Results revealed that the MMT-BSA coated Mg alloy AZ31 implants maintained their structural integrity and slight degradation after 120 d of post-implantation. A 100% survival rate for the rats was observed with no obvious toxic damages on the organs and tissues. Additionally, we proposed a sound coating formation mechanism. Considering the good corrosion protection and biocompatibility, the MMT-BSA coated Mg alloy AZ31 is a promising candidate material for biomedical implants.

Key words: Magnesium alloy, Hydrothermal synthesis, Corrosion resistance, Biocompatibility, Coating

Wang Jian, Cui Lanyue, Ren Yande, Zou Yuhong, Ma Jinlong, Wang Chengjian, Zheng Zhongyin, Chen Xiaobo, Zeng Rongchang, Zheng Yufeng. In vitro and in vivo biodegradation and biocompatibility of an MMT/BSA composite coating upon magnesium alloy AZ31[J]. J. Mater. Sci. Technol., 2020, 47: 52-67.

Figures/Tables 19

Table 1 Chemical composition (g L-1) of Hank’s solution.

NaCl	KCl	NaHCO₃	KH₂PO₄	Na₂HPO₄	D-Glucose	CaCl₂	MgSO₄	MgCl₂
8.0	0.4	0.35	0.06	0.0477	1.0	0.14	0.049	0.047

Fig. 1. Schematic illustration of preparation of MMT-BSA composite coating.

Fig. 2. Position of implanted samples.

Fig. 3. SEM morphologies and the corresponding EDS spectra of the (a, b) MMT and (c, d) MMT-BSA coatings, (e) FT-IR spectra and (f) XRD patterns of the MMT-BSA coating, BSA powder, MMT coating, MMT powder and Mg alloy AZ31.

Fig. 4. XPS broad survey of MMT coating (a) and MMT-BSA coating(b).

Fig. 5. HEA curves of Mg alloy AZ31, MMT and MMT-BSA coatings immersed in Hank’s for 5 d (a), variation in pH values (b) and accumulated Mg2+ ions released with immersion (c) for AZ31, MMT and MMT-BSA coatings in Hank’s solution for 1 d.

Fig. 6. FT-IR spectra of MMT and MMT-BSA coatings immersed in Hank’s for 5 d (a) and XRD patterns (b) of Mg alloy AZ31, MMT coating and MMT-BSA coating immersed in Hank’s for 5 d.

Fig. 7. SEM morphologies and the corresponding EDS spectra of Mg alloy AZ31 (a-f), MMT (g-l) and MMT-BSA (m-r) coatings immersed in Hank’s for 1, 3, and 5 d.

Fig. 8. Potentiodynamic polarization (PDP) curves of Mg alloy AZ31, MMT and MMT-BSA coatings immersed in Hank’s solution.

Table 2 Electrochemical parameters of the polarization curves.

Samples	β_a (mV dec^-1)	-β_c (mV dec^-1)	E_corr (V_SCE)	i_corr (A cm^-2)	R_p (Ω cm²)
AZ31	104.98	130.73	-1.41	6.27 × 10^-6	4.03 × 10⁶
MMT coating	51.50	168.28	-1.42	2.09 × 10^-6	8.20 × 10⁶
MMT-BSA coating	54.42	128.75	-1.40	7.65 × 10^-7	2.17 × 10⁷

Fig. 9. EIS and the fitted results for Mg alloy AZ31, MMT and MMT-BSA coatings: (a) Nyquist plots; (b) Bode plots of |Z| vs. frequency; (c) Bode plots of phase angle vs. frequency in Hank’s solution; equivalent circuits of the Mg alloy AZ31 (d); (e) MMT coating and the MMT-BSA coating.

Table 3 Electrochemical data obtained via equivalent circuit fitting of the EIS curves.

Samples	R_s (Ω cm²)	CPE₁ (Ω^-1 cm^-2 sⁿ)	n₁	R₁ (Ω cm²)	CPE₂ (Ω^-1 cm^-2 sⁿ)	n₂	R_ct (Ω cm²)	R_L (Ω cm²)	L (H cm²)
AZ31	91.09	7.92 × 10^-6	0.92	_	_	_	2.28 × 10³	1.98 × 10³	1.6 × 10³
MMT-coating	120.68	1.98 × 10^-5	0.39	172.5	6.08 × 10^-6	0.87	8.22 × 10³	_	_
MMT-BSA coating	101.9	1.61 × 10^-6	0.68	172.6	1.04 × 10^-5	0.68	1.57 × 10⁴	_	_

Fig. 10. (a) Absorbance value of hemoglobin, Hemolysis ratio (b) and dynamic clotting time curve (c) of Mg alloy AZ31, MMT and MMT-BSA coatings.

Fig. 11. Typical SEM images of platelet adhesion and corresponding EDS spectra of different samples: (a, b) Mg alloy AZ31; (c, d) MMT; (e, f) MMT-BSA coatings.

Fig. 12. Viability of MC3T3-E1 cells incubated for 24 h and 72 h (a) and CLSM images of live/dead staining incubated for 24 h with leach liquor of negative control and samples (b, c, d, e).

Fig. 13. Mg alloy AZ31, MMT coating and MMT-BSA coating in vivo: (a1-c1) Spiral CT scan 1 d; (a2-c2) 120 d; (a3-c3, a4-c4) SEM images 120 d; (a5-c5) EDS.

Fig. 14. H&E staining of myocardium, liver, lung, renal cortex, medulla and local muscle after 120 d of implantation of Mg alloy AZ31, MMT coating and MMT-BSA coating.

Fig. 15. PDP curves of Zn-MMT coating immersed in DMEM + 10% CS solution.

Table 4 Comparison of corrosion resistance of other biological coatings and BSA coatings on Mg alloys.

Materials	Coating	Solution	E_corr (V)	I_corr (A cm^-2)	Refs.
AZ31	Zn-MMT	DMEM	-1.38	2.86 × 10^-7	[46]
AZ31	(PVP/DNA) _n	SBF	-1.53	4.71 × 10^-6	[66]
AZ31	PDA-HA-BMP-2	PBS	-1.53	5.20 × 10^-5	[67]
Mg-4Li-1Ca	MAO/CS-3	Hank’s	-1.93	6.71 × 10^-6	[68]
AZ31	PEO/Mg-Zn-Al LDH	PBS	-0.68	8.59 × 10^-6	[69]
AZ31	MMT-BSA	Hank’s	-1.40	9.65 × 10^-7	present work

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