Citation: Schwartz, A.; Kossenko, A.; Zinigrad, M.; Danchuk, V.; Sobolev, A. Cleaning Strategies of Synthesized Bioactive Coatings by PEO on Ti-6Al-4V Alloys of Organic Contaminations. Materials 2023, 16, 4624. https://doi.org/10.3390/ ma16134624 Academic Editor: Camelia Ungureanu Received: 26 May 2023 Revised: 22 June 2023 Accepted: 24 June 2023 Published: 27 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Cleaning Strategies of Synthesized Bioactive Coatings by PEO on Ti-6Al-4V Alloys of Organic Contaminations Avital Schwartz 1 , Alexey Kossenko 1 , Michael Zinigrad 1 , Viktor Danchuk 2 and Alexander Sobolev 1, * 1 Department of Chemical Engineering, Ariel University, Ariel 4070000, Israel; avitals@ariel.ac.il (A.S.); kossenkoa@ariel.ac.il (A.K.); zinigrad@ariel.ac.il (M.Z.) 2 Physics Department, Faculty of Natural Sciences, Ariel University, Ariel 4076414, Israel; viktorde@ariel.ac.il * Correspondence: sobolev@ariel.ac.il; Tel.: +972-3-9143085 Abstract: The effect of various cleaning methods on coating morphology and their effectiveness in removing organic contaminants has been studied in this research. Bioactive coatings containing titanium oxides and hydroxyapatite (HAP) were obtained through plasma electrolytic oxidation in aqueous electrolytes and molten salts. The cleaning procedure for the coated surface was performed using autoclave (A), ultraviolet light (UV), radio frequency (RF), air plasma (P), and UV-ozone cleaner (O). The samples were characterized using scanning electron microscopy (SEM) with an EDS detector, X-ray photoelectron spectroscopy (XPS), X-ray phase analysis (XRD), and contact angle (CA) measurements. The conducted studies revealed that the samples obtained from molten salt exhibited a finer crystalline structure morphology (275 nm) compared to those obtained from aqueous electrolytes (350 nm). After applying surface cleaning methods, the carbon content decreased from 5.21 at.% to 0.11 at.% (XPS), which directly corresponds to a reduction in organic contaminations and a decrease in the contact angle as follows: A > UV > P > O. This holds true for both coatings obtained in molten salt (25.3 ◦ > 19.5 ◦ > 10.5 ◦ > 7.5 ◦ ) and coatings obtained in aqueous electrolytes (35.2 ◦ > 28.3 ◦ > 26.1 ◦ > 16.6 ◦ ). The most effective and moderate cleaning method is ozone treatment. Keywords: plasma electrolytic oxidation; titanium alloys; cleaning; hydroxyapatite; molten salt; organic contamination 1. Introduction Titanium and its alloys are the most widely used material in biomedical applications due to their excellent properties, such as high corrosion resistance, high specific strength, and low density [1–3]. Artificial joints, dental implants, and orthopedic/bone screws are common application fields for titanium and its alloys [4,5]. Since Ti is bioinert [6], it does not form strong bonds with soft and hard tissues, negatively affecting its bioactive and osseointegration properties and sometimes complicating its use in biomedical applications. To improve these properties various surface modification methods are employed to en- hance these properties [7,8], aimed at increasing the contact surface of biological tissue with the implanted material (sandblasting, chemical etching, etc.). As combined methods for improving the surface properties of implanted materials, the sol-gel method, plasma spraying, anodizing, PVD, and CVD are used [9,10]. The combination of these methods enhances the specific surface area of the implanted material and introduces bioactive prop- erties by incorporating various precursors into the coating composition. The introduced precursors usually consist of various combinations of calcium and phosphorus compounds (hydroxyapatite, tricalcium phosphate, etc.) [11–13]. Therefore, the modified surface is char- acterized by higher bioactivity and, as a result, an increased rate of osseointegration [14–17]. Bioactive coatings based on calcium and phosphorus compositions are utilized because they form compounds that closely resemble the chemical composition of human bone tis- sue [15,18]. However, it is crucial to remember that the applied coating must meet several Materials 2023, 16, 4624. https://doi.org/10.3390/ma16134624 https://www.mdpi.com/journal/materials