Review of the Effect of Surface Coating Modification on Magnesium Alloy Biocompatibility

Abstract

Magnesium alloy, as an absorbable and implantable biomaterial, has been greatly developed in the application field of biomaterials in recent years due to its excellent biocompatibility and biomechanics. However, due to the poor corrosion resistance of magnesium alloy in the physiological environment, the degradation rate will be unbalanced, which seriously affects the clinical use. There are two main ways to improve the corrosion resistance of magnesium alloy: one is by adding alloying elements, the other is by surface modification technology. Compared with adding alloy elements, the surface coating modification has the following advantages: (1) The surface coating modification is carried out without changing the matrix elements of magnesium alloy, avoiding the introduction of other elements; (2) The corrosion resistance of magnesium alloy can be improved by relatively simple physical, chemical, or electrochemical improvement. From the perspective of corrosion resistance and biocompatibility of biomedical magnesium alloy materials, this paper summarizes the application and characteristics of six different surface coating modifications in the biomedical magnesium alloy field, including chemical conversion method, micro-arc oxidation method, sol-gel method, electrophoretic deposition, hydrothermal method, and thermal spraying method. In the last section, it looks forward to the development prospect of surface coating modification and points out that preparing modified coatings on the implant surface combined with various modification post-treatment technologies is the main direction to improve biocompatibility and realize clinical functionalization.

Keywords: biocompatibility; corrosion resistance; implantable bio-metal materials; magnesium alloy; surface coating modification.

Figure 1

Comparison diagram of newly-born bone cells coated with (a,b) calcium phosphate around the culture. Reprinted with permission from Ref. [24]. Copyright 2019 Copyright Elsevier.

Figure 2

Mouse fibroblasts on Mg surface that had been pre-treated by soaking in M-SBF at 37 °C for 5 days. Fluorescence imaging of cells and cell spreading area as a function of culture time. Reprinted with permission from Ref. [25]. Copyright 2009 Copyright Elsevier.

Figure 3

SEM surface morphology of the magnesium fluoride-coated materials after 11 days of immersion in DMEM: (a) PM Mg, (b) cast Mg, and (c) AZ31 alloy. Reprinted with permission from Ref. [27]. Copyright 2011 Copyright Elsevier.

Figure 4

SEM images of blood platelet adhesion on the micro-arc oxidation (MAO) coating HA-containing coating: (a) SEM images with scale of 10μm, (b) SEM images with scale of 2μm. Reprinted with permission from Ref. [42]. Copyright 2018 Copyright Elsevier.

Figure 5

SEM analyses of (a) uncoated AZ31, (b) Nb2O5 coated AZ31 substrate. Reprinted with permission from Ref. [55]. Copyright 2014 Copyright Elsevier.

Figure 6

DAPI staining of nuclei of live osteoblast cells showing blue fluorescence on (a) uncoated and (b) Nb₂O₅ coated substrates after incubation with MG63 osteoblast cells for 24 h and (c) nuclei of live cells observed on Nb₂O₅ coated substrate after 48 h of incubation with MG63 osteoblast cells. (Ethidium bromide/acridine orange combined stain causes live cells to fluoresce green, whereas apoptotic cells cause the distinctive red-orange fluorescence.) Reprinted with permission from Ref. [55]. Copyright 2014 Copyright Elsevier.

Figure 7

Comparison of SEM micrographs of Mg alloy coated with HAP and uncoated with HAP: (a) Mg alloy uncoated with HAP, (b) Mg alloy coated with HAP. Reprinted with permission from Ref. [65]. Copyright 2020 Copyright Elsevier.

Figure 8

Shows the SEM micrograph of superhydrophobic hydroxyapatite coating. Reprinted with permission from Ref. [67]. Copyright 2018 Copyright Elsevier.

Figure 9

(a) Surface morphology of coating, (b) microstructure of coating section. Reprinted with permission from Ref. [82]. Copyright 2018 Copyright Elsevier.