Strategies to improve the corrosion resistance of microarc oxidation (MAO) coated magnesium alloys for degradable implants: Prospects and challenges T.S.N. Sankara Narayanan ⇑ , Il Song Park ⇑ , Min Ho Lee ⇑ Department of Dental Biomaterials and Institute of Oral Bioscience, Brain Korea 21 Project School of Dentistry, Chonbuk National University, Jeonju 561-756, South Korea article info Article history: Received 5 November 2012 Received in revised form 28 March 2013 Accepted 30 August 2013 Available online 5 September 2013 abstract The development of biodegradable implants is indeed fascinating and among the various types of materials used in this regard, mag- nesium and its alloys assume significance. However, the rapid cor- rosion, generation of a large volume of hydrogen gas, accumulation of the hydrogen bubbles in gas pockets adjacent to the implant, increase in local pH of the body fluid, are the major impediments in using them as an implant material. Hence, development of Mg/Mg alloy based degradable implants requires that (i) they should maintain sufficient mechanical strength and integrity until the affected part of body is healed; (ii) they should exhibit good resistance to corrosion in the body fluid during the initial periods of implantation and subsequently corrode in a controlled and uni- form fashion; and (iii) the corrosion products should not exceed the acceptable absorption level of the human body. Reducing the rate of corrosion of Mg is the most appropriate strategy and this can be achieved with the use of alloying, surface treatment/coating and mechanical processing. Surface treatment/coating is a viable approach as it not only enables improvement in corrosion resis- tance but also provides a suitable surface for better bone bonding and cell growth. Among the various surface modification processes, microarc oxidation (MAO) has received considerable attention since the protective oxide layer would delay the rate of corrosion attack during the initial period of implantation and, the decrease in the extent of hydrogen evolution would enhance the primary 0079-6425/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pmatsci.2013.08.002 ⇑ Tel./fax: +82 0632704040. E-mail addresses: tsnsn@rediffmail.com (T.S.N. Sankara Narayanan), ilsong@jbnu.ac.kr (Il Song Park), lmh@chnbuk.ac.kr (Min Ho Lee). Progress in Materials Science 60 (2014) 1–71 Contents lists available at ScienceDirect Progress in Materials Science journal homepage: www.elsevier.com/locate/pmatsci