Sealing the Pores of PEO Coating with Mg-Al Layered Double Hydroxide: Enhanced Corrosion Resistance, Cytocompatibility and Drug Delivery Ability

Abstract

In recent years, magnesium (Mg) alloys show a promising application in clinic as degradable biomaterials. Nevertheless, the poor corrosion resistance of Mg alloys is the main obstacle to their clinical application. Here we successfully seal the pores of plasma electrolytic oxidation (PEO) coating on AZ31 with Mg-Al layered double hydroxide (LDH) via hydrothermal treatment. PEO/LDH composite coating possess a two layer structure, an inner layer made up of PEO coating (~5 μm) and an outer layer of Mg-Al LDH (~2 μm). Electrochemical and hydrogen evolution tests suggest preferable corrosion resistance of the PEO/LDH coating. Cytotoxicity, cell adhesion, live/dead staining and proliferation data of rat bone marrow stem cells (rBMSCs) demonstrate that PEO/LDH coating remarkably enhance the cytocompatibility of the substrate, indicating a potential application in orthopedic surgeries. In addition, hemolysis rate (HR) test shows that the HR value of PEO/LDH coating is 1.10 ± 0.47%, fulfilling the request of clinical application. More importantly, the structure of Mg-Al LDH on the top of PEO coating shows excellent drug delivery ability.

In-Situ Growth of NiAl-Layered Double Hydroxide on AZ31 Mg Alloy towards Enhanced Corrosion Protection

“…Herein, we report a facile hydrothermal measurement to in-situ growth of NiAl-LDH nanocomposite on Mg alloy by use of alkaline solutions with three different nickel salts for preparation of a highly enhanced corrosion-resistant coating with an extraordinary low corrosion rate ( Figure 1 ). The NiAl-LDH coating prepared by nickel carbonate exhibits uniformly and vertically aligned nanoarrays with an extremely large impedance modulus at a low frequency of 0.1 Hz (| Z | f = 0.1 Hz ), 11.6 MΩ cm 2 , and a significantly low j corr down to 1.06 nA cm −2 in 3.5 wt % NaCl corrosive electrolyte, which outperforms the values of the foregoing achieved LDH coating on Mg alloy ( Table 1 ) [ 8 , 10 , 13 , 14 , 16 , 17 , 18 ]. The NiAl-LDH coatings were characterized, and the enhanced corrosion inhibition mechanism was proposed and discussed.…”

“…Recently, MgFe-LDH and MgCr-LDH films were also obtained on anodized AZ31 Mg alloy by in-situ growth measurement [ 10 ]. However, the orders of magnitude of the j corr of these in-situ grown LDH coatings are higher than −8, mostly range from −5 to −7 ( Table 1 ) [ 8 , 11 , 12 , 13 , 14 ]. To break the bottleneck of j corr , it is advisable to prepare carbonate-based LDHs film by attempting more different divalent or trivalent metallic cations.…”

Osteogenesis, angiogenesis and immune response of Mg-Al layered double hydroxide coating on pure Mg

“…S3 ). Our previous study revealed that cell viability decreased significantly when concentration of Mg 2+ higher than 20 mM or pH value higher than 8.5 [ 37 ]. The extract of pure Mg would experience a severe change of Mg 2+ concentration and pH value, thus leading to a severe cytotoxicity.…”

A Review on LDH-Smart Functionalization of Anodic Films of Mg Alloys

“…The elevated temperatures associated with the formation of PEO–LDH composite coatings would lead to a mismatch between the dissolution of PEO layers and the growth of Mg–Al LDH film [ 84 , 85 , 86 , 87 , 88 , 89 ]. This deficiency would restrict the large improvement in the protective properties of these materials.…”

“…Second, if the dissolution rate of the PEO coating is identical to the growth rate of the LDH film, this may cause a certain improvement in the protective properties due to the partial sealing of structural defects of PEO coating by LDH films. As an example, Peng et al [ 85 ] made a Mg–Al LDH film on the PEO-coated AZ31 Mg alloy by hydrothermal treatment at 293 K for 12 h using a solution with a pH of 12.8. PDP results in a phosphate-buffered saline solution indicated that the i corr of the PEO coating was only reduced from 9.45 × 10 −6 A cm −2 to 3.92 × 10 −6 A cm −2 upon the application of Mg–Al LDH film on the surface of PEO coating, suggesting a slight improvement in the corrosion resistance was achieved.…”