近年來，越來越多的3D列印技術應用於生醫組織工程。尤其金屬積層製造方面被認為是最具應用潛力的一項技術，其中功能性孔洞梯度支架扮演著重要角色，因為該技術製作的材料使植入物在病患體內能夠有效的減少排斥現象，並避免應力屏蔽效應發生。
本研究透過選擇性雷射燒熔技術以鈦合金製造梯度多孔性結構，並進行結構設計及參數研究。內容主要分成兩部分，第一部分為了有效控制梯度多孔性結構材料之45°剪切斷裂現象，將參數分為: 1.保持相同的整體材料孔隙度，改變高孔隙度層數及排列方式，2.探討高孔隙度層數減少時，無法產生45°剪切斷裂的極限層數，第二部分探討應變率效應對高孔隙度層數的影響。研究結果顯示，當整體材料孔隙度相同，高孔隙度層數不同排列時，高孔隙區連續層數較低，高孔隙度每層承受偏移角度變大，材料強度降低更快。而當高孔隙度區層數達到一層時，多孔材料已無空間生成45°斷裂面之裂紋，因此小裂紋沿界面生成，顯示吾人可以選擇適當的多孔性設計，控制沿45°破壞的現象。第二，高孔隙度層數下降到一定比例時，應變速率會提高一個級別，變成衝擊測試，造成材料塑性變形量大幅下降。研究結果亦發現，當高孔隙度層數由8層減少到4層時，降伏應力大幅上升1.5倍，顯示在此過程出現穩態轉變至非穩態的轉折點。

In recent years, a growing number of 3D-printing technology has been applied to biomedical tissue engineering. In particular, additive Manufacturing is considered to be the most potential technology for it. Furthermore, functionally graded porous scaffold is used to avoid stress shielding effect and reduce the rejective reactions on implant of patients. In this study, we use Ti-alloy to manufacture functionally graded porous scaffolds by Selective Laser Melting, then design the structural of scaffolds and investigate the mechanical properties of each sample. The content is divided into two parts. First of all, in order to control the occurrence of shear fracture of functionally graded porous scaffolds under compression test, we use different number of high porosity layers and arrangement for parameters. Secondly, we investigate the effect of the strain rate effect on the number of high porosity layers. We have demonstrated that when the porosity of the whole material is the same and the arrangement of high porosity region is different, the sample with low continuous high porosity layer results in faster failure owing to the larger offset angle. Furthermore, the porous material has no space to develop 45° Shear fracture as the number of high porosity layer becomes one. Hence small cracks are formed along the interface. This indicates that we can control the occurrence of 45° Shear fracture by the design of high porosity layers. What’s more, as the strain rate increases a level and becomes an impact test high porosity layer drops to a certain percentage, resulting in a significant decrease in the amount of plastic deformation of the material. Finally, it is found that the yield stress increases by a factor of 1.5 when the number of high porosity layers are reduced from 8 layers to 4 layers. This shows a turning point of a process from a steady-state to an unsteady transition.

[1] X. Tan, Y. Tan, C. Chow, S. Tor, W. J. M. S. Yeong, and E. C, "Metallic powder-bed based 3D printing of cellular scaffolds for orthopaedic implants: A state-of-the-art review on manufacturing, topological design, mechanical properties and biocompatibility," vol. 76, pp. 1328-1343, 2017.
[2] A. Kumar, K. Nune, L. Murr, and R. J. I. M. R. Misra, "Biocompatibility and mechanical behaviour of three-dimensional scaffolds for biomedical devices: process–structure–property paradigm," vol. 61, no. 1, pp. 20-45, 2016.
[3] F. P. Melchels, K. Bertoldi, R. Gabbrielli, A. H. Velders, J. Feijen, and D. W. Grijpma, "Mathematically defined tissue engineering scaffold architectures prepared by stereolithography," Biomaterials, vol. 31, no. 27, pp. 6909-6916, 2010.
[4] X.-Y. Zhang, G. Fang, and J. J. M. Zhou, "Additively manufactured scaffolds for bone tissue engineering and the prediction of their mechanical behavior: A review," vol. 10, no. 1, p. 50, 2017.
[5] J. An, J. E. M. Teoh, R. Suntornnond, and C. K. Chua, "Design and 3D Printing of Scaffolds and Tissues," (in English), Engineering, Review vol. 1, no. 2, pp. 261-268, Jun 2015.
[6] X. Wang et al., "Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: a review," Biomaterials, vol. 83, pp. 127-141, 2016.
[7] A. Ataee, Y. C. Li, D. Fraser, G. S. Song, and C. E. Wen, "Anisotropic Ti-6Al-4V gyroid scaffolds manufactured by electron beam melting (EBM) for bone implant applications," (in English), Materials & Design, Article vol. 137, pp. 345-354, Jan 2018.
[8] C. Yan, L. Hao, A. Hussein, and P. J. J. o. t. m. b. o. b. m. Young, "Ti–6Al–4V triply periodic minimal surface structures for bone implants fabricated via selective laser melting," vol. 51, pp. 61-73, 2015.
[9] W. van Grunsven, E. Hernandez-Nava, G. C. Reilly, and R. Goodall, "Fabrication and mechanical characterisation of titanium lattices with graded porosity," Metals, vol. 4, no. 3, pp. 401-409, 2014.
[10] S. J. Li et al., "Functionally Graded Ti-6Al-4V Meshes with High Strength and Energy Absorption," (in English), Advanced Engineering Materials, Article vol. 18, no. 1, pp. 34-38, Jan 2016.
[11] B. V. Krishna, S. Bose, and A. Bandyopadhyay, "Low stiffness porous Ti structures for load-bearing implants," Acta biomaterialia, vol. 3, no. 6, pp. 997-1006, 2007.
[12] N. Sudarmadji, J. Y. Tan, K. F. Leong, C. K. Chua, and Y. T. Loh, "Investigation of the mechanical properties and porosity relationships in selective laser-sintered polyhedral for functionally graded scaffolds," (in English), Acta Biomaterialia, Article vol. 7, no. 2, pp. 530-537, Feb 2011.
[13] S. Giannitelli, D. Accoto, M. Trombetta, and A. Rainer, "Current trends in the design of scaffolds for computer-aided tissue engineering," Acta biomaterialia, vol. 10, no. 2, pp. 580-594, 2014.
[14] B. Bucklen, W. Wettergreen, E. Yuksel, M. J. V. Liebschner, and P. Prototyping, "Bone-derived CAD library for assembly of scaffolds in computer-aided tissue engineering," vol. 3, no. 1, pp. 13-23, 2008.
[15] N. Yang, S. Wang, L. Gao, Y. Men, and C. Zhang, "Building implicit-surface-based composite porous architectures," Composite Structures, vol. 173, pp. 35-43, 2017.
[16] L. Wang, J. Kang, C. Sun, D. Li, Y. Cao, and Z. Jin, "Mapping porous microstructures to yield desired mechanical properties for application in 3D printed bone scaffolds and orthopaedic implants," Materials & Design, vol. 133, pp. 62-68, 2017.
[17] S. Van Bael et al., "The effect of pore geometry on the in vitro biological behavior of human periosteum-derived cells seeded on selective laser-melted Ti6Al4V bone scaffolds," Acta biomaterialia, vol. 8, no. 7, pp. 2824-2834, 2012.
[18] N. Chantarapanich et al., "Scaffold library for tissue engineering: a geometric evaluation," vol. 2012, 2012.
[19] S. Rajagopalan and R. A. J. M. I. A. Robb, "Schwarz meets Schwann: design and fabrication of biomorphic and durataxic tissue engineering scaffolds," vol. 10, no. 5, pp. 693-712, 2006.
[20] B. Derby, "Printing and prototyping of tissues and scaffolds," Science, vol. 338, no. 6109, pp. 921-926, 2012.
[21] K. MONKOVA, P. MONKA, I. ZETKOVA, P. HANZL, D. J. D. T. o. C. S. MANDULAK, and Engineering, "Three Approaches to the Gyroid Structure Modelling as a Base of Lightweight Component Produced by Additive Technology," no. cmsam, 2017.
[22] F. S. L. Bobbert et al., "Additively manufactured metallic porous biomaterials based on minimal surfaces: A unique combination of topological, mechanical, and mass transport properties," (in English), Acta Biomaterialia, Article vol. 53, pp. 572-584, Apr 2017.
[23] I. Maskery et al., "A mechanical property evaluation of graded density Al-Si10-Mg lattice structures manufactured by selective laser melting," Materials Science and Engineering: A, vol. 670, pp. 264-274, 2016.
[24] C. J. Han et al., "Continuous functionally graded porous titanium scaffolds manufactured by selective laser melting for bone implants," (in English), Journal of the Mechanical Behavior of Biomedical Materials, Article vol. 80, pp. 119-127, Apr 2018.
[25] R. Hasan, R. A. Mines, E. Shen, S. Tsopanos, and W. Cantwell, "Comparison on compressive behaviour of aluminium honeycomb and titanium alloy micro lattice blocks," in Key Engineering Materials, 2011, vol. 462, pp. 213-218: Trans Tech Publ.
[26] W.-M. Chen et al., "Lattice Ti structures with low rigidity but compatible mechanical strength: Design of implant materials for trabecular bone," International Journal of Precision Engineering and Manufacturing, vol. 17, no. 6, pp. 793-799, 2016.
[27] R. Ochola, K. Marcus, G. Nurick, and T. J. C. S. Franz, "Mechanical behaviour of glass and carbon fibre reinforced composites at varying strain rates," vol. 63, no. 3-4, pp. 455-467, 2004.
[28] P. H. Bischoff, S. J. M. Perry, and structures, "Compressive behaviour of concrete at high strain rates," vol. 24, no. 6, pp. 425-450, 1991.
[29] Y. Wu et al., "Structural design and mechanical response of gradient porous Ti-6Al-4V fabricated by electron beam additive manufacturing," vol. 158, pp. 256-265, 2018.