Yan Chunze, Hao Liang, Hussein Ahmed, Young Philippe
State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China; College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, Devon, United Kingdom.
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, Devon, United Kingdom.
J Mech Behav Biomed Mater. 2015 Nov;51:61-73. doi: 10.1016/j.jmbbm.2015.06.024. Epub 2015 Jul 9.
Triply periodic minimal surface (TPMS) structures have already been shown to be a versatile source of biomorphic scaffold designs. Therefore, in this work, Ti-6Al-4V Gyroid and Diamond TPMS lattices having an interconnected high porosity of 80-95% and pore sizes in the range of 560-1600 μm and 480-1450 μm respectively were manufactured by selective laser melting (SLM) for bone implants. The manufacturability, microstructure and mechanical properties of the Ti-6Al-4V TPMS lattices were evaluated. Comparison between 3D micro-CT reconstructed models and original CAD models of the Ti-6Al-4V TPMS lattices shows excellent reproduction of the designs. The as-built Ti-6Al-4V struts exhibit the microstructure of columnar grains filled with very fine and orthogonally oriented α' martensitic laths with the width of 100-300 nm and have the microhardness of 4.01 ± 0.34 GPa. After heat treatment at 680°C for 4h, the α' martensite was converted to a mixture of α and β, in which the α phase being the dominant fraction is present as fine laths with the width of 500-800 nm and separated by a small amount of narrow, interphase regions of dark β phase. Also, the microhardness is decreased to 3.71 ± 0.35 GPa due to the coarsening of the microstructure. The 80-95% porosity TPMS lattices exhibit a comparable porosity with trabecular bone, and the modulus is in the range of 0.12-1.25 GPa and thus can be adjusted to the modulus of trabecular bone. At the same range of porosity of 5-10%, the moduli of cortical bone and of the Ti-6Al-4V TPMS lattices are in a similar range. Therefore, the modulus and porosity of Ti-6Al-4V TPMS lattices can be tailored to the levels of human bones and thus reduce or avoid "stress shielding" and increase longevity of implants. Due to the biomorphic designs, and high interconnected porosity and stiffness comparable to human bones, SLM-made Ti-6Al-4V TPMS lattices can be a promising material for load bearing bone implants.
三重周期极小曲面（TPMS）结构已被证明是生物形态支架设计的一个通用来源。因此，在本研究中，通过选择性激光熔化（SLM）制造了用于骨植入物的Ti-6Al-4V类螺旋体和菱形TPMS晶格，其具有80-95%的相互连通高孔隙率，孔径分别在560-1600μm和48-1450μm范围内。对Ti-6Al-4V TPMS晶格的可制造性、微观结构和力学性能进行了评估。Ti-6Al-4V TPMS晶格的三维显微CT重建模型与原始CAD模型之间的比较显示出设计的优异再现性。增材制造的Ti-6Al-4V支柱呈现出柱状晶粒的微观结构，其中填充有非常细小且正交取向的α'马氏体板条，宽度为100-300nm，显微硬度为4.01±0.34GPa。在680°C下热处理4小时后，α'马氏体转变为α和β的混合物，其中占主导比例的α相以宽度为500-800nm的细板条形式存在，并被少量狭窄的暗β相相间区域隔开。此外，由于微观结构的粗化，显微硬度降至3.71±0.35GPa。孔隙率为80-95%的TPMS晶格与松质骨具有相当的孔隙率，模量在0.12-1.25GPa范围内，因此可以调整到松质骨的模量。在5-10%的相同孔隙率范围内，皮质骨和Ti-6Al-4V TPMS晶格的模量处于相似范围。因此，Ti-6Al-4V TPMS晶格的模量和孔隙率可以调整到人体骨骼的水平，从而减少或避免“应力屏蔽”并提高植入物的使用寿命。由于其生物形态设计、高相互连通孔隙率以及与人体骨骼相当的刚度，SLM制造的Ti-6Al-4V TPMS晶格可能是用于承重骨植入物的一种有前途的材料。
