Microwave assisted Magnesium Phosphate coating on AZ31
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1
The University of Toledo, Mechanical, Industrial and Manufacturing Engineering (MIME), United States
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2
The University of Toledo, Division of Dentistry, United States
Introduction: Magnesium and its alloys attracted tremendous interests as potential biodegradable implant materials for orthopedic and devices. However the extremely high degradation rate of magnesium alloys in physiological environment can result in the mechanical failure of implants before the remodeling of bones occurs. Calcium phosphates, especially hydroxyapatite and brushite have been extensively studied as the protective coatings[1]. Magnesium phosphate is the alternative to calcium phosphate and also a promising candidate for biomedical applications. To best of our knowledge, applying magnesium phosphate to tailor the degradation rate of magnesium alloys and improve their biological responses has not been systemically studied. In addition, microwave radiation can significantly accelerate the deposition kinetics and shorten the coating process to minutes[2].
Materials and Methods: Commercially available AZ31 alloy was polished and ultrasonically cleaned by ethanol and DI water. The coating bath was prepared by dissolving 2.564g Mg(NO3)2·6H2O , 0.7198g NaH2PO4 in 100ml DI water. The pH value of the coating bath was adjusted to 5.6 by 1M NaOH solution. Next, a vessel containing 50 ml solution and AZ31 substrates was placed in a microwave system (MARS 230/60) and heated by microwave for 30 min at 80°C, 120°C and 160°C respectively. The coated samples were characterized by XRD, FTIR, and SEM coupled with EDS.
Results and Discussion: Fig. 1(a) presents X-ray diffraction pattern of bare and treated AZ31 substrates. The diffraction peaks of the coating prepared at 80 °C and 120 °C correspond to the newberyite (MgHPO4·3H2O). In contrast to coating prepared at lower temperature, the film produced at 160°C showed biphasic structure consisting with both newberyite and trimagnesium phosphate tetrahydrate (Mg3(PO4)2·4H2O) phases. It can be speculated that phase transformation happened when temperature increased to 160°C. The IR spectra of magnesium phosphate coatings are showed in Fig. 1(b). The absorption peaks attributed to phosphate band (PO43 –) were centered at 1161cm-1, 1054 cm-1 and 1014 cm-1.The coating deposited at 80°C and 120°C revealed comparable morphologies, except the smaller particles were achieved in the coating treated at 120°C. As shown in Fig. 2(a) and (b), both coatings comprised micron sized newberyite precipitates with polyhedral and tabular structures. At 160°C however, the AZ31 substrate was uniformly covered with flower-like trimagnesium phosphate tetrahydrate. EDS results indicated the major elements present in the coating are Mg, P and O.
Conclusion: Magnesium phosphate coatings have been successfully deposited onto AZ31 magnesium alloy substrate using a microwave assisted coating process. The phase composition and morphology of the magnesium phosphate coating can be differed due to the treatment temperature. The degradation behavior and cellular response are being studied currently.
Fig. 1 (a) XRD patterns of the bare and treated samples (b) FTIR spectra of the MgP coated samples.
Fig. 2 SEM images and EDS spectra of MgP coated AZ31 substrates, (a) 80°C-30min, (b) 120°C-30min and (c) 160°C-30min.
References:
[1] Shadanbaz, Shaylin, and George J. Dias. "Calcium phosphate coatings on magnesium alloys for biomedical applications: a review." Acta Biomaterialia 8.1 (2012): 20-30.
[2] Ren, Yufu, Huan Zhou, Maryam Nabiyouni, and Sarit B. Bhaduri. "Rapid coating of AZ31 magnesium alloy with calcium deficient hydroxyapatite using microwave energy." Materials Science and Engineering: C 49 (2015): 364-372.
Keywords:
Biocompatibility,
Surface modification,
Biodegradable metal
Conference:
10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016.
Presentation Type:
Poster
Topic:
Metallic biomaterials and alloys
Citation:
Ren
Y and
Bhaduri
S
(2016). Microwave assisted Magnesium Phosphate coating on AZ31.
Front. Bioeng. Biotechnol.
Conference Abstract:
10th World Biomaterials Congress.
doi: 10.3389/conf.FBIOE.2016.01.02546
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Received:
27 Mar 2016;
Published Online:
30 Mar 2016.