Corrosion resistance of a composite polymeric coating applied on biodegradable AZ31 magnesium alloy q A. Zomorodian a,⇑ , M.P. Garcia b , T. Moura e Silva a,c , J.C.S. Fernandes a , M.H. Fernandes b , M.F. Montemor a a ICEMS/DEQ, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b Laboratory for Bone Metabolism and Regeneration, Faculty of Dental Medicine, University of Porto, Porto, Portugal c ISEL, Department of Mechanical Engineering, 1959-007 Lisboa, Portugal article info Article history: Available online xxxx Keywords: Polymeric coating Magnesium alloy Hydroxyapatite Corrosion resistance Cytocompatibility abstract The high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide simultaneously corro- sion resistance and enhanced biocompatibility. In this work, a composite coating containing polyether imide, with several diethylene triamine and hydroxyapatite contents, was applied on AZ31 magnesium alloys pre-treated with hydrofluoric acid by dip coating. The coated samples were immersed in Hank’s solution and the coating performance was studied by electrochemical impedance spectroscopy and scan- ning electron microscopy. In addition, the behavior of MG63 osteoblastic cells on coated samples was investigated. The results confirmed that the new coatings not only slow down the corrosion rate of AZ31 magnesium alloys in Hank’s solution, but also enhance the adhesion and proliferation of MG63 osteoblastic cells, especially when hydroxyapatite nanoparticles were introduced in the coating formulation. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. 1. Introduction Biomedical implants such as screws, plates and pins are used for healing bone defects. For these applications it is possible to use metallic materials that degrade slowly in the physiological envi- ronment, being absorbed by the organism. This procedure elimi- nates the need for a second surgery for removal of the implant from the body [1]. One of these materials is magnesium and its al- loys, which show mechanical properties similar to those of the bone, and can degrade in the physiological environment. Magne- sium ions are naturally found in the bone tissue and play an essen- tial role in human metabolism and bone healing [2]. Thus, its release is indeed beneficial for current body functions. Hard-tissue repair typically requires implantation of the mate- rial for at least 12 weeks [1]. From this point of view, the use of magnesium is quite limited because it is very active and corrodes very fast in the physiological fluids, increasing the risk of excess H 2 (g) release inside the body [2]. In addition, the high corrosion rate of magnesium and its alloys affect negatively the mechanical properties of the implant before total healing of the bone defects. One of the ions present in the physiological environment that pro- motes the corrosion of magnesium alloys is the chloride ion. As a consequence of the corrosion process, Mg dissolves and, in the presence of hydroxyl ions released by the cathodic processes, leads to the formation of magnesium hydroxide (natural protective layer). However, in the presence of excess chloride ions, Mg can also be converted into magnesium chloride, which is more soluble in aqueous solution than magnesium hydroxide, resulting in an in- crease of the corrosion rate. Avoiding this phenomenon is essential to delay the corrosion process. One possibility consists of the for- mation of surface layers with good corrosion resistance. It has been reported that pre-treatment of Mg alloys such as AZ31 with hydro- fluoric acid promotes the formation of a magnesium-fluoride-rich coating, increasing the corrosion resistance in aggressive solutions [2–4]. However, this pre-treatment is not enough to protect the Mg alloy for long periods in aggressive media, and corrosion proceeds very fast in a short term. It has been demonstrated that the most effective method to delay corrosion activity on Mg alloys is the application of surface coatings. Nevertheless it is well known that the coating performance relies heavily on appropriate pre-treat- ments that functionalize the surface [2], improving adhesion. Organic coatings are attractive for biomedical applications as they offer protection against corrosion and can be functionalized for ‘‘smart’’ functions, such as controlled drug delivery and loading with organic biomolecules. Many polymers such as poly(L-lactic acid) (PLLA), polycaprolactone (PCL) and poly(glycolic acid) (PGA) have been approved for human clinical uses, including small 1742-7061/$ - see front matter Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actbio.2013.02.036 q Part of the Biodegradable Metals Conference 2012 Special Issue, edited by Professor Frank Witte and Professor Diego Mantovani. ⇑ Corresponding author. Tel.: +0351 21 841 97 69. E-mail address: amir.zomorodian@ist.utl.pt (A. Zomorodian). Acta Biomaterialia xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Acta Biomaterialia journal homepage: www.elsevier.com/locate/actabiomat Please cite this article in press as: Zomorodian A et al. Corrosion resistance of a composite polymeric coating applied on biodegradable AZ31 magnesium alloy. Acta Biomater (2013), http://dx.doi.org/10.1016/j.actbio.2013.02.036