Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Nanostructured amorphous magnesium phosphate/poly (lactic acid) composite coating for enhanced corrosion resistance and bioactivity of biodegradable AZ31 magnesium alloy Yufu Ren a, ⁎ , Elham Babaie b , Sarit B. Bhaduri a,c a Department of Mechanical, Industrial and Manufacturing Engineering, The University of Toledo, Toledo, OH, USA b Department of Bioengineering, The University of Toledo, Toledo, OH 43606, USA c Division of Dentistry, The University of Toledo, Toledo, OH, USA ARTICLE INFO Keywords: AZ31 magnesium alloy Amorphous magnesium phosphate Poly-lactic acid Composite coating ABSTRACT Due to the combination many interesting properties, magnesium alloys have attracted considerable interest as suitable metallic biomaterials for bioresorbable orthopedic implants. Nevertheless, their fast degradation in physiological environments pose challenge for their practical applications. Here, we report that spin coating of composites of nano amorphous magnesium phosphate (nAMP) and poly (lactic acid) (PLA) on AZ31 magnesium alloy. The idea is to use the nAMP/PLA composite film while tailoring the degradation and enhancing the bioactivity of magnesium alloys. SEM examinations show that as-deposited nAMP/PLA film is smooth, crack-free and the nAMP particles are well distributed in PLA matrix. The electrochemical test including potentiodynamic polarization and EIS associated with immersion test results reveal that the corrosion activities of nAMP/PLA coated AZ31 magnesium alloy in SBF are markedly suppressed. Furthermore, it is seen that massive bone-like apatite precipitates formed on surface of nAMP/PLA coated sample, which is indicative for the superior bio- mineralization capability achieved by nAMP/PLA nanocomposite coating. Thus, the nAMP/PLA composite coating has great potential to be employed as the protective and bioactive coating on biodegradable magnesium alloys for orthopedic applications. 1. Introduction Over the last decade, magnesium alloys have attracted tremendous interest as biodegradable orthopedic implant materials, due to their low density, suitable elastic moduli and degradability in physiological en- vironment [1–3]. The controlled degradation of magnesium implants in vivo could eliminate the second surgical intervention to avoid potential risks associated with such procedures. The high degradation kinetics of magnesium alloys, however is a double-edged sword. The rapid de- gradation of magnesium alloys in physiological condition usually leads to the locally elevated pH value, formation of hydrogen gas cavities and premature mechanical failure of implants [3–5]. To retard the gas evolution and enhance the corrosion resistance of magnesium alloys, various forms of surface modification have been proposed. The pro- tective coatings include, but are not limited to chemical conversion coatings [6], bioceramic coatings [7–11], polymeric coatings [12–14] and hybrid coatings [15–17]. Of special interest are biodegradable polymeric coatings which can not only serve as the barrier layer, but can perform the drug delivery vehicles [18]. A case in point is poly- lactic acid (PLA) which is already cleared by the FDA for clinical ap- plications [19]. The degradation of PLA through bulk erosion me- chanism is relatively slow, and the degradation product (lactic acid) is metabolically digestible [20]. To improve degradation resistance of magnesium alloy, PLA coatings have been deposited on magnesium and its alloys via various methods, such as spin coating, dip coating and spray [21–23]. In general, the PLA film prepared by spin coating is more uniform with less defects, thereby providing better corrosion re- sistance. However, the degradation of PLA generates the acidic product that can lower the local pH value, subsequently hinder the biominer- alization and osseointegration [24]. Therefore, incorporating the nano- sized bioactive ceramic in PLA matrix is a feasible solution to overcome its drawback, while regulating the degradation of magnesium alloy si- multaneously. Magnesium phosphate compounds are the alternative to the well- known calcium phosphates and have not been extensively explored. Amorphous magnesium phosphate (AMP) is a sub-set of MgO-P 2 O 5 group, which has been attracting increasing interests due to their out- standing biocompatibility, biodegradability and bioactivity [25,26]. https://doi.org/10.1016/j.porgcoat.2018.01.014 Received 25 July 2017; Received in revised form 10 January 2018; Accepted 13 January 2018 ⁎ Corresponding author. E-mail address: Yufu.Ren@rockets.utoledo.edu (Y. Ren). Progress in Organic Coatings 118 (2018) 1–8 0300-9440/ © 2018 Elsevier B.V. All rights reserved. T