Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility

doi:10.1016/j.jmst.2019.01.012

Abstract

Abstract:

Porous metal scaffolds play an important role in the orthopedic field, due to their wide applications in prostheses implantation. Some previous studies showed that the scaffolds with trabecular bone structure reconstructed via computed tomography had satisfactory biocompatibility. However, the reverse modeling scaffolds were inflexible for customized design. Therefore, a top-down designing biomimetic bone scaffold with favorable mechanical performances and cytocompatibility is urgently demanded for orthopedic implants. An emerging additive manufacturing technique, selective laser melting, was employed to fabricate the trabecular-like porous Ti-6Al-4 V scaffolds with varying irregularities (0.05-0.5) and porosities (48.83%-74.28%) designed through a novel Voronoi-Tessellation based method. Micro-computed tomography and scanning electron microscopy were used to characterize the scaffolds’ morphology. Quasi-static compression tests were performed to evaluate the scaffolds’ mechanical properties. The MG63 cells culture in vitro experiments, including adhesion, proliferation, and differentiation, were conducted to study the cytocompatibility of scaffolds. Compressive tests of scaffolds revealed an apparent elastic modulus range of 1.93-5.24 GPa and an ultimate strength ranging within 44.9-237.5 MPa, which were influenced by irregularity and porosity, and improved by heat treatment. Furthermore, the in vitro assay suggested that the original surface of the SLM-fabricated scaffolds was favorable for osteoblasts adhesion and migration because of micro scale pores and ravines. The trabecular-like porous scaffolds with full irregularity and higher porosity exhibited enhanced cells proliferation and osteoblast differentiation at earlier time, due to their preferable combination of small and large pores with various shapes. This study suggested that selective laser melting-derived Ti-6Al-4 V scaffold with the trabecular-like porous structure designed through Voronoi-Tessellation method, favorable mechanical performance, and good cytocompatibility was a potential biomaterial for orthopedic implants.

Key words: Irregular porous structure, Selective laser melting, Voronoi-Tessellation, Mechanical performance, In vitro study

Huixin Liang, Youwen Yang, Deqiao Xie, Lan Li, Ning Mao, Changjiang Wang, Zongjun Tian, Qing Jiang, Lida Shen. Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility[J]. J. Mater. Sci. Technol., 2019, 35(7): 1284-1297.

Figures/Tables 16

Table 1 Chemical composition of the Ti-6Al-4 V ELI powder (mass %).

Ti	Al	V	O	N	C	H	Fe
Bal	5.90	3.91	0.12	0.05	0.08	0.012	0.3

Fig. 1. (a) SEM micrograph and (b) particle size distribution of Ti-6Al-4 V powders.

Fig. 2. (a) Schematic of irregularly porous structure modeling, (b) schematic of selective laser melting process and (c) as-built Ti-6Al-4 V scaffolds by SLM.

Table 2 Optimized process parameters used in the SLM fabrication.

Laser power	Scan speed	Hatch spacing	Layer thickness	Laser focus	Atmosphere
180 W	1350 mm/s	0.1 mm	0.03 mm	0.1 mm	Ar

Fig. 3. Stress-strain curve to determine characteristic values from compression testing of porous structure.

Fig. 4. (a, c, d) SEM micrographs with different amplifications of as-built Ti-6Al-4 V scaffolds after ultrasonic cleaning and (b) 3D model.

Table 3 Comparison between the designed and experimental characteristics of scaffolds (n = 3; D: difference value).

	ε	Strut thickness (μm)		Volume (mm³)		Surface area (mm²)		Specific surface area (mm^-1)			Porosity (%)
	ε	CAD	μCT	CAD	μCT	CAD	μCT	CAD	μCT	D	CAD	μCT	D
Set 1	0.06	361 ± 35	611 ± 52	85.49	113.23	890.32	794.75	10.41	7.01	-3.4	70.92	61.49	-9.43
	0.25	352 ± 62	487 ± 49	87.93	109.81	884.33	830.24	10.06	7.56	-2.5	70.01	62.65	-7.36
	0.5	368 ± 81	464 ± 41	89.67	106.67	929.53	895.92	10.37	8.4	-1.97	69.5	63.95	-5.55
Set 2	0.5	730 ± 56	797 ± 34	133.08	150.44	789.53	756.71	5.93	5.03	-0.9	54.73	48.83	-5.9
		550 ± 61	630 ± 21	95.04	107.29	709.16	673.54	7.46	6.28	-1.18	67.67	63.51	-4.16
		380 ± 49	468 ± 39	59.98	75.63	588.31	547.28	9.81	7.23	-2.58	79.6	74.28	-5.32

Fig. 5. Relationship between pore size distribution and irregularity for set 1 of as-built scaffolds: (a) ε = 0.06; (b) ε = 0.25; (c) ε = 0.5.

Fig. 6. Compression test results of as-built scaffolds with various irregularities, porosities and different heat treatment processes: (a, b) stress-strain curves; (c, d) calculated elastic modulus; (e, f) ultimate strength.

Fig. 7. Viability and proliferation of MG63 cells on porous Ti-6Al-4 V scaffolds with different irregularities and porosities: (a, b) fluorescence microscopy images after being cultured for 1 d (live cells appeared as bright green dots); (c, d) CCK-8 assay results after being cultured for 1, 3 and 5 d, n = 3 (sample size), #Significant difference (one-way ANOVA: p<0.05).

Fig. 8. SEM micrographs of cell adhesion morphologies on scaffolds with different irregularities and porosities after being cultured for 3 d (cell bridging behaviors were highlighted by red arrows).

Fig. 9. ALP activity of MG63 cells on different porous Ti-6Al-4 V scaffold designs after being cultured for 14 d, n = 3 (sample size), #Significant difference (one-way ANOVA: p<0.05).

Fig. 10. (a) Reconstructed 3D model of healthy spongy bone with, (b) trabecular-like porous structure with homogeneity in porosity, (c) reconstructed 3D model of gradient structure of trabecular bone and (d) trabecular-like porous structure with gradient in porosity.

Fig. 11. Forming mechanism of powder adhesions on struts.

Fig. 12. Comparisons between design and fabrication of scaffolds with different irregularities: (a, b) sections from the same location; (c, d) unit cells of 2.4 mm × 2.4 mm × 2.4 mm.

Fig. 13. FEA results for von Mises stress field of scaffolds.

References

[1]	M. Schieker, W. Mutschler, Der Unfallchirurg 109 (2006) 715-732
[2]	H.M. Frost, Angle Orthod. 74(2004) 3-15
[3]	S.J. Hollister, Adv. Mater. 21(2009) 3330-3342
[4]	M.J. Olszta, X. Cheng, S.S. Jee, R. Kumar, Y.Y. Kim, M.J. Kaufman, E.P. Douglas, L.B. Gower, Mater. Sci. Eng. R 58 (2007) 77-116
[5]	L.L. Hench, J. Am. Ceram. Soc. 74(1991) 1487-1510
[6]	X.H. Liu, P.X. Ma, Ann. Biomed. Eng. 32(2004) 477-486
[7]	K. Alvarez, H. Nakajima, Materials (Basel) 2(2009) 790-832
[8]	Y. Yang, F. Yuan, C. Gao, P. Feng, L. Xue, S. He, C. Shuai, J. Mech. Behav.Biomed. Mater. 82(2018) 51-60
[9]	Y. Yang, X. Guo, C. He, C. Gao, C. Shuai, ACS Biomater. Sci. Eng. 4(2018) 1046-1054
[10]	Y. Yang, P. Wu, Q. Wang, H. Wu, Y. Liu, Y. Deng, Y. Zhou, C. Shuai, Materials 9 (2016) 1-10
[11]	M. Textor, C. Sittig, V. Frauchiger, S. Tosatti, D.M. Brunrtte, in: D.M. Brunrtte, P. Tengvall, M. Textor, P. Thomsen (Eds.), Titanium in Medicine, Springer, Berlin 2001, pp. 171-230
[12]	W. Xue, B.V. Krishna, A. Bandyopadhyay, S. Bose, Acta Biomater. 3(2007) 1007-1018
[13]	S.M. Giannitelli, D. Accoto, M. Trombetta, A. Rainer, Acta Biomater. 10(2014) 580-594
[14]	X. Wang, S. Xu, S. Zhou, W. Xu, M. Leary, P. Choong, M. Qian, M. Brandt, Y.M. Xie, Biomaterials 83 (2016) 127-141
[15]	V. Karageorgiou, D. Kaplan, Biomaterials 26 (2005) 5474-5491
[16]	B.S. Van, Y.C. Chai, S. Truscello, M. Moesen, G. Kerckhofs, O.H. Van, J.P. Kruth, J. Schrootrn, Acta Biomater. 8(2012) 2824-2834
[17]	Z. Wang, C. Wang, C. Li, Y. Qin, L. Zhong, B. Chen, Z. Li, H. Liu, F. Chang, J. Alloys. Compd. 717(2017) 271-285
[18]	D.K. Pattanayak, A. Fukuda, T. Matsushita, M. Takemoto, S. Fujibayashi, K. Sasaki, N. Nishida, T. Nakamura, T. Kokubo, Acta Biomater. 7(2011) 1398-1405
[19]	A. Cheng, A. Humayun, D.J. Cohen, B.D. Boyan, Z. Schwartz, Biofabrication, 6(2014), 045007
[20]	M.L. Mather, S.P. Morgan, L.J. White, H. Tai, W. Kockenberger, S.M. Howdle, K.M. Shakesheff, J.A. Crowe, Biomed. Mater. 3(2008) 015011
[21]	Z. Chen, Z. Su, S. Ma, X. Wu, Z. Luo, Comput. Meth. Prog.Biomed. 88(2007) 123-130
[22]	X.Y. Kou, S.T. Tan, Comput. Aided Des. 42(2010) 930-941
[23]	S. Nachtrab, S.C. Kapfer, C.H. Arns, M. Madadi, K. Mecke, G.E. Schr?der-Turk, Adv. Mater. 23(2011) 2633-2637
[24]	X. Zhang, L. Tang, Z. Liu, Z. Jiang, Y. Liu, Y. Wu, Mech. Mater. 104(2017) 73-84
[25]	L. Lin, X. Wang, X. Zeng, CMES Comput. Model. Eng. Sci. 98(2014) 203-220
[26]	H. Honda, T. Nagai, J. Biochem. 157(2015) 129-136
[27]	M. Fantini, M. Curto, C.F. De, Virtual Phys. Prototyp. 11(2016) 77-90
[28]	S. Gómez, M.D. Vlad, J. López, E. Fernández, Acta Biomater. 42(2016) 341-350
[29]	K.F. Leong, C.M. Cheah, C.K. Chua, Biomaterials 24 (2003) 2363-2378
[30]	J.P. Kruth, G. Levy, F. Klocke, T.H.C. Childs, CIRP Ann. Manuf. Technol. 56(2007) 730-759
[31]	L. Thijs, F. Verhaeghe, T. Craeghs, J.V. Humbeeck, J.P. Kruth, Acta Mater. 58(2010) 3303-3312
[32]	P.H. Warnke, T. Douglas, P. Wollny, E. Sherry, M. Steiner, S. Galonska, S.T. Becker, I.N. Springer, J. Wiltfang, S. Sivananthan, Tissue Eng. Part. C 15 (2009) 115-124
[33]	G. Wang, L. Shen, J. Zhao, H. Liang, D. Xie, Z. Tian, C. Wang, ACS Biomater. Sci. Eng. 4(2018) 719-727
[34]	B. Vandenbroucke, J.P. Kruth, Rapid Prototyp. J. 13(2007) 196-203
[35]	S. Langlois, F. Coeure, I. Material. Characterization. J. Appl. Electrochem. 19(1989) 43-50
[36]	I. Mircheski, M. Gradi?ar, Comput. Methods Biomech. Biomed. Eng. 19(2016) 1531-1540
[37]	Z. Xiao, Y. Yang, R. Xiao, Y. Bai, C. Song, D. Wang, Mater. Des. 143(2018) 27-37
[38]	C. Yan, L. Hao, A. Hussein, D. Raymont, Int. J. Mach. Tools Manuf. 62(2012) 32-38
[39]	S. McKown, Y. Shen, W.K. Brookes, C.J. Sutcliffe, W.J. Cantwell, G.S. Langdon, G.N. Nurick, M.D. Theobald, Int. J. Impact. Eng. 35(2008) 795-810
[40]	L.J. Gibson, M.F. Ashby, Cellular Solids: Structure and Properties (second ed.), Cambridge University Press, Cambridge(1999) 175-231
[41]	Y.Z. Yang, J.M. Tian, J.T. Tian, Z.Q. Chen, X.J. Deng, D.H. Zhang, J. Biomed. Mater. Res. 52(2000) 333-337
[42]	D.A. Hollander, W.M. Von, T. Wirtz, R. Sellei, B. Schmidt-Rohlfing, O. Paar, H.J. Erli Biomaterials 27 (2006) 955-963
[43]	M. Fantini, M. Curto, Int. J. Interact. Des. Manuf. 12(2018) 585-596
[44]	S.L. Sing, F.E. Wiria, W.Y. Yeong, Robot. Comput. Integr. Manuf. 49(2018) 170-180
[45]	L. Mullen, R.C. Stamp, W.K. Brooks, E. Jones, C.J. Sutcliffe, J. Biomed. Mater. Res. Part B 89(2009) 325-334
[46]	P. Sevilla, C. Aparicio, J.A. Planell, F.J. Gil, J. Alloys. Compd. 439(2007) 67-73
[47]	E.F. Morgan, H.H. Bayraktar, T.M. Keaveny, J. Biomech. 36(2003) 897-904
[48]	X.N. Gu, Y.F. Zheng, Front. Mater. Sci. China 4 (2010) 111-115
[49]	J. Shi, J. Yang, Z. Li, L. Zhu, L. Li, X. Wang, J. Alloys. Compd. 728(2017) 1043-1048
[50]	L. Zhu, L. Li, J. Shi, Z. Li, J. Yang, Am. J. Transl. Res. 10(2018) 3443-3454
[51]	E. Onal, J.E. Frith, M. Jurg, X. Wu, A. Molotnikov, Metals 8 (2018) 1-21
[52]	J. Parthasarathy, B. Starly, S. Raman, A. Christensen, J. Mech. Behav.Biomed. Mater. 3(2010) 249-259
[53]	R.W. McCalden, J.A. McGlough, M.B. Barker, C.M. Court-Brown, J. Bone Joint Surg. Am. 75(1993) 1193-1205
[54]	P. Mercelis, J.P. Kruth, Rapid Prototyp. J. 12(2006) 254-265
[55]	T. Vilaro, C. Colin, J.D. Bartout, Metall. Mater. Trans. A, 4(2011) 3190-3199
[56]	B. Vrancken, L. Thijs, J.P. Kruth, H.J. Van, J. Alloys. Compd. 54(2012) 177-185
[57]	A. Costa, Geophys. Res. Lett. 33(2006) 1-5
[58]	L. Shor, S. Gü?eri, X. Wen, M. Gandh, W. Sun, Biomaterials 28 (2007) 5291-5297
[59]	M.R. Dias, P.R. Fernandes, J.M. Guedes, S.J. Hollister, J. Biomech. 45(2012) 938-944
[60]	W. Xue, B.V. Krishna, A. Bandyopadhyay, S. Bose, Acta Biomater. 3(2007) 1007-1018
[61]	M. Rumpler, A. Woesz, J.W.C. Dunlop, D.J.T. Van, P. Fratzl, J. Royal Soc. Interf. 5(2008) 1173-1180
[62]	E.G. Khaled, M. Saleh, S. Hindocha, M. Griffin, W.S. Khan, Open Orthop. J. 5(2011) 289-295
[63]	Z. Schwartz, P. Raz, G. Zhao, Y. Barak, M. Tauber, H. Yao, B.D. Boyan, J. Bone Joint Surg. Am. 90(2008) 2485-2498
[64]	K.C. Nune, A. Kumar, R.D.K. Misra, S.J. Li, Y.L. Hao, R. Yang, Colloids Surf. B Biointerfaces 150 (2017) 78-88
[65]	J. Lv, Z. Jia, J. Li, Y. Wang, J. Yang, P. Xiu, K. Zhang, H. Cai, Z. Liu, Adv. Eng. Mater. 17(2015) 1391-1398
[66]	S.J. Roberts, Y. Chen, M. Moesen, J. Schrooten, F.P. Luyten, Stem Cell Res. 7(2011) 137-144