Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci A crack-free anti-corrosive coating strategy for magnesium implants under deformation Kwang-Hee Cheon a , Chao Gao b , Min-Ho Kang a , Hyun-Do Jung c , Tae-Sik Jang d , Hyoun-Ee Kim a,e , Yaning Li b, ⁎ , Juha Song d, ⁎ a Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea b Department of Mechanical Engineering, University of New Hampshire, Durham, NH, 03824 USA c Liquid Processing & Casting Technology R&D Group, Korea Institute of Industrial Technology, Incheon 406-840, Republic of Korea d School of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, 637457, Singapore e Advanced Institutes of Convergence Technology, Seoul National University, Suwon-si, 443-270, Republic of Korea ARTICLE INFO Keywords: Magnesium Corrosion resistance Deformation Hard coating Biomaterials ABSTRACT Surface patterns can be used as a selective coating platform on metal surfaces, in particular, under various deformation conditions because they induce local strain gradients along with pattern geometry. In this study, hard and flexible coating materials were introduced to regions with small and large deformations, respectively, on patterned magnesium (Mg) surfaces. Despite significant deformation, a polymer-ceramic coating on patterned Mg maintained its protection, as opposed to a ceramic coating on a flat Mg surface. Our proposed approach can be implemented in various Mg-based medical-device platforms by optimizing surface patterns on Mg depending on their loading conditions for clinical use. 1. Introduction Functional coating is a common technique for altering the surface properties of a material. Functional coatings offer enhanced mechanical protection, resistance to chemical deterioration, biocompatibility, and responsive performances to external stimuli [1–3]. However, the coating layers also cause intrinsic mechanical problems such as buck- ling, surface cracking, and delamination upon deformation. Therefore, a coating method that improves the mechanical stability of the coated product under various operation conditions is greatly desired [4]. The interfaces of different materialities, especially hard–soft interfaces, are challenging because of the large deformation discrepancy between the two materials under an external force [4,5]. To avoid hard–soft inter- facial problems, the stress and strain can be gradually distributed through functionally graded layers placed between the hard and soft materials, thereby suppressing interfacial delamination [6]. The contact stability might also improve by new flexible coating materials that better match the underlying material [7,8]. Despite the proven ad- vantages of these approaches, the limited thickness and fatigue of coating layers reduce the long-term durability of the devices in practical use. To the best of our knowledge, these issues remain unresolved [9]. The hard–soft interface problem also occurs for magnesium (Mg)- based implants when coating layers are introduced to Mg to improve corrosion resistance. Although Mg-based implants have attracted much attention based on their good biocompatibility, biodegradability, and suitable mechanical properties, they quickly corrode when exposed to water in physiological environments, producing hydrogen gas and hy- droxide ions. Such corrosion often provokes acute and chronic in- flammation responses in hosts [10–12]. The corrosion behavior of Mg implants has been moderated by protective coating methods, such as tunable coating layers, with the coating layers often improving the biological performance, providing corrosion barriers, and invoking multifunctional effects (e.g., drug delivery) in the Mg implants [13–15]. Common coating materials include biopolymers such as poly-L-lactic acid, poly(lactide-co-glycolide), polycaprolactone, and polyetherimide (PEI) and bioceramics such as hydroxyapatite (HA) and tricalcium phosphate [15–19]. However, similar to various coating systems in other fields, biological coatings on implants must meet the practical requirements for clinical use. For example, in orthopedic applications, the coating materials of degradable Mg implants must be mechanically stable against implant deformation during surgical operations and physiological loading conditions after fixation in the body. In addition to the load-bearing role of the implant, the substrate will be deformed post-surgery by bone regenerated through the healing process [16,20,21]. In this context, flexible biopolymer-coating materials are more mechanically stable to deformations than bioactive ceramic https://doi.org/10.1016/j.corsci.2017.12.030 Received 21 September 2017; Received in revised form 21 November 2017; Accepted 21 December 2017 ⁎ Corresponding authors. E-mail addresses: Yaning.li@nhu.edu (Y. Li), songjuha@ntu.edu.sg (J. Song). Corrosion Science xxx (xxxx) xxx–xxx 0010-938X/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Cheon, K.-h., Corrosion Science (2017), https://doi.org/10.1016/j.corsci.2017.12.030