In Vitro Biodegradation and Mechanical Properties of Mg-Zn Alloy and Mg-Zn-Hydroxyapatite Composite Produced by Mechanic
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INTRODUCTION
MAGNESIUM (Mg) stands out as a potential candidate for temporary implants in biomedical applications due to its light weight, as well as its elastic modulus and compressive yield strength, which are compatible with those of natural bone.[1] The density of Mg is 1.738 g/cm3, which is only slightly less than that of natural bone (1.8 to 2.1 g/cm3),[2] while the elastic modulus of pure Mg is 45 GPa[3,4] as compared to human bone (30 to 57 GPa).[5] Although Mg, Fe, and Zn are essential nutritional elements for a healthy body, the recommended daily intake of Mg for adults (240 to
EMEE MARINA SALLEH and HUSSAIN ZUHAILAWATI are with the Biomaterials Niche Area, School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia. Contact e-mail: [email protected] SITI NOOR FAZLIAH MOHD NOOR is with the Cranofacial and Biomaterials Science Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Bertam, 13200 Kepala Batas, Penang, Malaysia EMEE MARINA SALLEH and NORINSAN KAMIL OTHMAN are with the School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia Manuscript submitted May 29, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
420 mg/day) is up to 52.5 times more than that of Fe (8 to 18 mg/day) and Zn (8 to 11 mg/day).[1,6,7] In addition, the elastic modulus of Mg alloys (41 to 48 GPa) is closer to that of natural bone than that of Fe (~211 GPa) and Zn (~90 GPa).[8,9] This mismatch of elastic moduli can cause the implant to carry a greater portion of the load resulting in stress shielding within the surrounding bone.[10] This biomechanical incompatibility may result in critical clinical issues, including early implant loosening, damage to the healing process, skeletal thickening, and chronic inflammation.[11] Therefore, reducing the corrosion rate of Mg and its alloys in body fluids is a vital issue to be addressed before Mg-based materials can be used as degradable implants. The preparation of protective coatings on the substrate is one of the effective routes in enhancing the corrosion resistance of Mg and its alloys.[12] A sequence of techniques has been adopted for the surface modification of Mg alloys, including hydrothermal treatment, alkali-heat-treatment, thermal spray coating, ion implantation, anodizing coating, and so on.[13–15] Tomozawa and Hiromoto (2011) reported that hydroxyapatite (HA) coatings on pure Mg could be attained by hydrothermal treatment using a C10H12N2O8Na2Ca (Ca-EDTA) solution. The protectiveness of the coating toward corrosion attacks increased with a growth of dome-shaped precipitates containing apatite and the formation of a thin
magnesium hydroxide (Mg(OH)2) layer.[16] However, the mechanical reliability of the coating was not reported in their study. Currently, surface modification via apatite conversion film is one of the promising approaches in improving the corrosion resistance of Mg-based materials.[17] Yet, this
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