Enhanced Mechanical Properties and Corrosion Behavior of Biodegradable Mg-Zn/HA Composite
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TRODUCTION
MAGNESIUM (Mg) alloys have attracted considerable attention for biomaterial applications due to their low density, inherent biocompatibility, and resemblance of mechanical properties to human bone. Magnesium is able to degrade and to be safely absorbed in the physiological media, and excess Mg can be efficiently filtered by the kidneys.[1,2] To date, a number of approaches have been developed to produce biodegradable Mg alloy with adjustable in vitro and in vivo corrosion rates, while the mechanical integrity is not compromised. Another important point for a biomaterial is the ability of the implant to establish bonding with the surrounding bone tissue, which is bioactivity of the implant.[3,4] Therefore, it seems necessary to increase the bioactivity of Mg-based materials. An approach to this challenge might be the application of metal matrix composite (MMC). The advantage of using MMCs as biomaterials is the adjustable mechanical properties (Young’s modulus and compressive and tensile strength) as well as the adjustable corrosion behavior by choosing EMEE MARINA SALLEH, HUSSAIN ZUHAILAWATI, and SIVAKUMAR RAMAKRISHNAN 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] BRIJ KUMAR DHINDAW is with the School of Minerals Metallurgical and Materials Engineering, Indian Institute of Technology, Bhubaneswar, 751007, India. Manuscript submitted September 1, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
suitable reinforcement materials. Introducing bioactive particles containing Ca is known to reduce the susceptibility of Mg to corrode when added in amounts of a few tenths weight percent.[5,6] As a natural bone composition, bioactive hydroxyapatite (HA; Ca10(PO4)6(OH)2) is known to possess a low solubility in body environment. HA seems to be an appropriate reinforcement particle in Mg-based implants, as HA presents a good ability to induce the deposition of Ca-P compounds that can increase the surface biocompatibility and bioactivity of the Mg alloy matrix materials.[7–9] Witte et al.[10] produced MMC made of AZ91D alloy reinforced with 20 wt pct HA powder by mixing the raw powders and subsequent extrusion at 673 K (400 C) to a diameter of 18 mm. From the study, corrosion tests revealed that HA particles stabilized the corrosion rate and exhibited more uniform corrosion attack in both artificial sea water and cell solutions. Cocultivation of AZ91D-HA revealed that the human bone derived cells; cells of osteoblast lineage and cells of macrophage lineage adhered, proliferated, and survived on the corroding surface of AZ91D-HA composite. However, the presence of aluminum (Al) has been shown to increase estrogen-related gene expression in human breast cancer cells when cultured in a laboratory setting.[2,5] In summary, biodegradable and cytocompatible Al-free Mg-based implants with adjustable mechanical and corrosion properties might be achieved by incorporatin
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