Nanostructured surfaces
Surface roughness and wettability of PEO-coated Mg alloys in different alkali solutions
Husak Ye.V.1, Oleshko O.M.1, Dudko J.S.1
1Sumy State University, 2, Rymsky-Korsakov Str., Sumy 40007, Ukraine 
E-mail: evgenia.husak@gmail.com 

Introduction. Magnesium (Mg) and Mg alloys considered as perspective materials for biodegradable implant development but fast and uncontrolled corrosion limited its clinical application. Plasma electrolytic oxidation (PEO) is a high-voltage electrochemical process that can provide protective coating over Mg implants [1]. Alkaline silicate, sodium fluoride, and phosphate electrolytes are recently used for PEO due to impact on mechanical and protective properties of the coating. Additionally, PEO can provide porous surface topography that provide adequate environment for cell adhesion and proliferation. 
Objectives. The objective of current study was to evaluate surface parameters of Mg after PEO in different alkali solutions.
Methods. All chemicals have been purchased from Sigma Aldrich and used as received. Pure Mg (99.9%) alloy used as substrate for PEO in following solutions: Sol 1 (Na2SiO3, NH4F and NaOH), Sol 2 (Na2SiO3, NH4F, and Ca(OH)2) and Sol 3 (Na2HPO4 and NaOH). PEO process performed with following parameters: current density - 0.1 A cm−2 and final voltage - 200, 250, 275, and 300 V for 10 min. Contact angle (CA) measurements were made using a video-based optical contact angle-measuring instrument. Surface roughness was determined by the tactile stylus method using a surface roughness tester. The arithmetic mean of the sum of roughness profile values (Ra, µm) was measured.
Results. The results showed statistically significant increases (p < 0.0001) the surface roughness in the case of Sol 2 300 V (2.10±0.15) and Sol 3 300 V (2.88±0.3) samples among obtained coatings. 
The contact angle for the samples Sol 1 and Sol 2 characterized as the surface with high wettability. Samples Sol 3 refers to the surface with low wettability.
Conclusion. The Mg treated under Sol 2 with final voltage 300 V showed the higher roughness value and complete wettability. The hydrophilicity of obtained coating and high roughness made them suitable for biomedical applications.
Acknowledgements. This research supported by H2020 MSCA-RISE-2017 project “NanoSurf 777926” and Ukraine MESU Grant # 0119U100770.

1. Gh. Barati Darband et al. Plasma electrolytic oxidation of magnesium and its alloys: Mechanism, properties and applications // Journal of Magnesium and Alloys. – 2017. - Volume 5, Issue 1. – P. 74-132