Citation: Pawlowski, L.; Ro´ sciszewska, M.; Majkowska-Marzec, B.; Ja ˙ zd ˙ zewska, M.; Bartma ´ nski, M.; Zieli ´ nski, A.; Tybuszewska, N.; Samsel, P. Influence of Surface Modification of Titanium and Its Alloys for Medical Implants on Their Corrosion Behavior. Materials 2022, 15, 7556. https:// doi.org/10.3390/ma15217556 Academic Editors: Mikhail Zheludkevich and Hideki Hosoda Received: 20 September 2022 Accepted: 24 October 2022 Published: 27 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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 Influence of Surface Modification of Titanium and Its Alloys for Medical Implants on Their Corrosion Behavior Lukasz Pawlowski 1 , Magda Ro´ sciszewska 2 , Beata Majkowska-Marzec 2 , Magdalena Ja ˙ zd˙ zewska 2 , Michal Bartma ´ nski 2 , Andrzej Zieli ´ nski 2, * , Natalia Tybuszewska 2 and Pamela Samsel 2 1 Department of Construction Materials, Institute of Manufacturing and Materials Technology, Faculty of Mechanical Engineering and Ship Technology, Gda´ nsk University of Technology, 80-233 Gda´ nsk, Poland 2 Department of Biomaterials Technology, Institute of Manufacturing and Materials Technology, Faculty of Mechanical Engineering and Ship Technology, Gda´ nsk University of Technology, 80-233 Gda´ nsk, Poland * Correspondence: andrzej.zielinski@pg.edu.pl; Tel.: +48-501329368 Abstract: Titanium and its alloys are often used for long-term implants after their surface treatment. Such surface modification is usually performed to improve biological properties but seldom to increase corrosion resistance. This paper presents research results performed on such metallic materials modified by a variety of techniques: direct voltage anodic oxidation in the presence of fluorides, micro-arc oxidation (MAO), pulse laser treatment, deposition of chitosan, biodegradable Eudragit 100 and poly(4-vinylpyridine (P4VP), carbon nanotubes, nanoparticles of TiO 2 , and chitosan with Pt (nano Pt) and polymeric dispersant. The open circuit potential, corrosion current density, and potential values were determined by potentiodynamic technique, and microstructures of the surface layers and coatings were characterized by scanning electron microscopy. The results show that despite the applied modifications, the corrosion current density still appears in the region of very low values of some nA/cm 2 . However, almost all surface modifications, designed principally for the improvement of biological properties, negatively influence corrosion resistance. The reasons for observed effects can vary, such as imperfections and permeability of some coatings or accelerated degradation of biodegradable deposits in simulated body fluids during electrochemical testing. Despite that, all coatings can be accepted for biological applications, and such corrosion testing results are presumed not to be of major importance for their applications in medicine. Keywords: titanium; titanium oxide; carbon nanotubes; nano platinum; chitosan; polyamine; polymethacrylate; electrophoretic deposition; corrosion testing; microstructure 1. Introduction Titanium and its alloys are well-known as resistant to general corrosion in many environments. Because of that and other outstanding features such as high biocompatibility, suitable mechanical properties except for wear resistance, and lightweight, they have become the best biomaterials for long-term endoprostheses or their components. However, they may appear prone to localized corrosion, wear corrosion, and general corrosion, in particular at low pH values and in saline-containing environments, i.e., just during the inflammation state [1–3]. There have been some papers in the last few years describing corrosion parame- ters of different coatings deposited or layers created on titanium [1,4–15] and its alloys: Ti6Al4V [16–23], Ti13Nb13Zr [14,24–27]. The coatings were designed and produced particu- larly to enhance corrosion resistance [1,4,6–9,11,16–19,21–24] or the corrosion characteristics were determined only to verify whether and to what extent the applied coating may affect the degradation process [5,10,12–15,20,25]. The main difference between coated materials was the presence or the absence of an artificial titanium oxide layer created by oxidation in different conditions [1,3,5–11,15,19,20] such as direct voltage anodic oxidation, micro- arc oxidation (MAO), or hydrothermal oxidation. The coatings other than rutile/anatase Materials 2022, 15, 7556. https://doi.org/10.3390/ma15217556 https://www.mdpi.com/journal/materials