Magnesium Alloys With Tunable Interfaces as Bone Implant Materials

Abstract

Magnesium (Mg) based biodegradable materials are a new generation orthopedic implant materials that are intended to possess same mechanical properties as that of bone. Mg alloys are considered as promising substitutes to permanent implants due to their biodegradability in the physiological environment. However, rapid corrosion rate is one of the major constraints of using Mg alloys in clinical applications in spite of their excellent biocompatibility. Approaches to overcome the limitations include the selection of adequate alloying elements, proper surface treatment, surface modification with coating to control the degradation rate. This review focuses on current advances on surface engineering of Mg based biomaterials for biomedical applications. The review begins with a description of corrosion mechanism of Mg alloy, the requirement for appropriate surface functionalization/coatings, their structure-property-performance relationship, and suitability for biomedical applications. The control of physico-chemical properties such as wettability, surface morphology, surface chemistry, and surface functional groups of the coating tailored by various approaches forms the pivotal part of the review. Chemical surface treatment offers initial protection from corrosion and inorganic coating like hydroxyapatite (HA) improves the biocompatibility of the substrate. Considering the demand of ideal implant materials, multilayer hybrid coatings on Mg alloy in combination with chemical pretreatment or inorganic HA coating, and protein-based polymer coating could be a promising technique to improve corrosion resistance and promote biocompatibility of Mg-based alloys.

Keywords: biomedical application; corrosion; interfacial engineering; magnesium alloy; surface coating.

Figure 1

Physio-chemical properties of biodegradable Mg alloys for biomedical applications.

Figure 2

(A) Several forms of corrosion and (B) corrosion mechanism of CaP coated Mg substrate in physiological environment.

Figure 3

Schematic illustration of interfacial engineering of untreated Mg alloys.

Figure 4

Effect of surface roughness on cellular behavior.

Figure 5

(A) Illustration of number of scientific publications from 2008 to 2018 using the search terms “magnesium” and “biomedical applications”. Data analysis was performed on 14 August 2019 using Scopus search system. (B) Basic requirements of biomaterials.

Figure 6

Schematic illustration of various coatings: (Left) polymer coatings: Col, CS—bioactive coatings, PLA, PLGA, PCL, PDA-bioinert coatings and (Right) biomimetic coatings (Left figure: Reprinted with the permission; Li et al., 2018). Copyright 2018, Elsevier.

Figure 7

Potentiodynamic polarization curves of PCL, PLA, and uncoated AZ91 Mg alloy in SBF solution. Reprinted with permission (Chen et al., 2011). Copyright 2011, IOP publishing.

Figure 8

Schematic structural formula of Bio-MOF coating on Mg alloy. Reprinted with permission (Liu et al., 2019). Copyright 2019, Elsevier.

Figure 9

Schematic of cellular response in different environment in various timescale: (A) osteoblast cells with physico-chemical interaction, (B) cell attachment with integrin binding, and (C) key steps in osseointegration and bone TE. Adapted with permission from Pioletti (2010).

Figure 10

Cell viability of uncoated and hybrid coated AZ31 Mg alloy for different immersion periods. Reprinted with permission (Zhu et al., 2017). Copyright 2017, MDPI.

Figure 11

SKP map of pristine: uncoated mild steel (MS), 3-[(methacryloyloxy)propyl] trimethoxysilane (MEMO): 2-(methacryloyloxy) ethyl phosphate (EGMP) M:E 1:1 and M:E 3:7 samples and gold on Al as reference. Reprinted with permission (Kannan et al., 2010). Copyright 2010, Elsevier.

Figure 12

Schematic illustration of bone remodeling on Mg through signaling pathways in the microenvironment regulating the cross talk of osteoblast to osteoclast.

Figure 13

Osteoblastic cell morphology of hybrid coating on Mg sample. (A) Bare Mg, (B) pure PEI, (C) PEI-15% silica, and (D) PEI-30% silica coated Mg specimens after 6 h cell attachment. Reprinted with permission (Kang et al., 2016). Copyright 2016, IOP publishing.

Figure 14

Confocal microscopy of scaffolds: (a) PA66 scaffold, (b) n-HA/GF/PA66 scaffold (X200), (c) n-HA/GF/PA66 scaffold (X500), and (d) n-HA/GF/PA66 scaffold (X1000) after 4d cell culture. Reprinted with permission (Su et al., 2013). Copyright 2013, Elsevier.

Figure 15

Radiography examination of composite coated Mg alloy implant in the femur of rabbit for different time periods. Yellow arrows, periosteal reaction/callus; green arrows, hydrogen bubble; blue arrows, residual implant. (a–c) Anteroposterior view of femurs in the experimental group; (e–g) lateral view of femurs in the experimental group; (d,h) anteroposterior and lateral view of femurs in the control group (Liu et al., 2020).