Magnesium is an alkaline earth light metal with good biocompatibility and osteoconductivity. It is one of the essential minerals for the human body. However, pure magnesium is not suitable for artificial biomaterials since its low mechanical properties and corrosion resistance. Composites of magnesium and its alloys with bioceramics have been developed to enhance desired properties. In this work, magnesium alloy (AZ31) and hydroxyapatite (HA) composites were fabricated using microwave energy of 2.45 GHz at 1.4 kW microwave power for 15 min exposure time in argon atmosphere. Biodegradable metal matrix composites (BMMCs) of three compositions; AZ31 with 10, 15 and 20 wt% hydroxyapatite, were explored. The role of nano-hydroxyapatite in microwave heating of BMMCs was analyzed and observed that heating rate increased as HA content increased in the BMMCs. It happened due to the higher dielectric loss of HA than AZ31. The high dielectric loss enhanced the microwave absorption in the green compact of BMMCs and raised the temperature at the same exposure time and microwave power. Microwave heating mechanism of BMMCs was also tried to understand. Moreover, these three BMMCs were characterized for their microstructural, mechanical properties and corrosion behaviour. The XRD and SEM results revealed that the major phases are Mg and HA, while in AZ31/20HA, one minor phase of the β-Ca3(PO4)2 is observed. AZ31/20HA showed the highest density and microhardness among the three compositions. In contrast, AZ31/15HA exhibited the highest compressive strength, Young's modulus and corrosion resistance. The reason for reducing AZ31/20HA compressive strength is the formation of the β-Ca3(PO4)2 phase since it shows lesser compressive strength than HA phase, which reduces the compressive strength of BMMC. Similarly, β-TCP degrades faster than HA due to its high solubility in simulated body fluid, which reduces the corrosion resistance of AZ31/20HA. However, the noble achievement of this study is the porosity gradient developed in the microwave processed BMMCs. The porosity gradient was obtained due to specific microwave heating characteristics; material gets heated from core to surface. Porosity gradient could be the desirable attribute of BMMCs for orthopedic applications. It enhances the osteogenesis reactions, increases surface area for more ion exchange from artificial material to host tissue and helps in tissue in growth.
Shivani Gupta is a Senior Research Fellow at Indian Institute of Technology Roorkee, India and she is going to finish her Doctor of Philosophy. She has done her B.Tech with honor and was awarded Gold Medal in her Master's. She visited The Pennsylvania State University, USA, as an Exchange Visiting Scholar under SPARC scheme. Her research areas are manufacturing processes, process optimization, powder metallurgy, microwave materials processing, biomaterials, characterization, modeling and simulation.
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