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Designing and manufacturing of porous spinal cages using Ti6A14V foamed metal
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Open cell Ti6Al4V foams with varying porosities (50, 60 and 70%) were prepared at sintering temperatures between 1200 and 1350 °C using ammonium bicarbonate particles (315 - 500 .m) as space holder. Two different biomedical grade commercial, gas atomized spherical Ti6Al4V powders were used to prepare foams. Powder 1 was in size range of between 45 - 150 .m and Powder 2 in size range of between 30 - 90 .m. The foams were sintered under argon atmosphere in a tightly enclosed tube furnace. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macro pores (300 - 500 .m) and micro pores (1 - 30 .m). Compression tests of foam samples have shown that increasing sintering temperature or decreasing porosity increased the elastic modulus, yield and compressive strength and failure strain. The improvement in the mechanical properties of foams prepared using smaller size Ti6Al4V powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. The foam prepared with optimum porosity, pore size and mechanical properties for bone in-growth was further used to produce prototype porous spinal cages which are widely used in spinal surgery for vertebrae fixation. The geometries and size of the prototype spinal cages were determined through the measurements taken from human vertebrae. The foams for spinal cage preparation were first prepared in the form of plates and then core-drilled using water jet based on the design geometrical parameters determined for each vertebra segment.