Ti-6Al-4V triply periodic minimal surface structures for bone implants fabricated via selective laser melting.

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.

[1]  Tadashi Kokubo,et al.  Pore throat size and connectivity determine bone and tissue ingrowth into porous implants: three-dimensional micro-CT based structural analyses of porous bioactive titanium implants. , 2006, Biomaterials.

[2]  Carolin Körner,et al.  Compression-compression fatigue of selective electron beam melted cellular titanium (Ti-6Al-4V). , 2011, Journal of biomedical materials research. Part B, Applied biomaterials.

[3]  B. Stucker,et al.  A comparison of the tensile, fatigue, and fracture behavior of Ti–6Al–4V and 15-5 PH stainless steel parts made by selective laser melting , 2013 .

[4]  Katia Bertoldi,et al.  Mathematically defined tissue engineering scaffold architectures prepared by stereolithography. , 2010, Biomaterials.

[5]  Mariana Calin,et al.  Selective laser melting of in situ titanium–titanium boride composites: Processing, microstructure and mechanical properties , 2014 .

[6]  J. P. Li,et al.  A novel porous Ti6Al4V: characterization and cell attachment. , 2005, Journal of biomedical materials research. Part A.

[7]  Shivakumar Raman,et al.  Mechanical evaluation of porous titanium (Ti6Al4V) structures with electron beam melting (EBM). , 2010, Journal of the mechanical behavior of biomedical materials.

[8]  Clemens A van Blitterswijk,et al.  Effects of the architecture of tissue engineering scaffolds on cell seeding and culturing. , 2010, Acta biomaterialia.

[9]  J. Planell,et al.  Comparison of the mechanical properties between tantalum and nickel–titanium foams implant materials for bone ingrowth applications , 2007 .

[10]  H. Maier,et al.  On the mechanical behaviour of titanium alloy TiAl6V4 manufactured by selective laser melting: Fatigue resistance and crack growth performance , 2013 .

[11]  Heat treatment of Ti6Al4V produced by Selective Laser Melting: Microstructure and mechanical properties , 2012 .

[12]  M. Neo,et al.  Osteoinduction of porous bioactive titanium metal. , 2004, Biomaterials.

[13]  A. Burstein,et al.  The elastic and ultimate properties of compact bone tissue. , 1975, Journal of biomechanics.

[14]  N. Nomura,et al.  Microstructures and Mechanical Properties of Porous Titanium Compacts Prepared by Powder Sintering. , 2002 .

[15]  H. Schwarz.  Gesammelte mathematische Abhandlungen , 1970 .

[16]  J. J. Grote,et al.  Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic. , 1986, Biomaterials.

[17]  Ryan B. Wicker,et al.  Characterization of Ti–6Al–4V open cellular foams fabricated by additive manufacturing using electron beam melting , 2010 .

[18]  Ahmed Hussein,et al.  Design and additive manufacturing of cellular lattice structures , 2011 .

[19]  R. Singer,et al.  Cellular Ti-6Al-4V structures with interconnected macro porosity for bone implants fabricated by selective electron beam melting. , 2008, Acta biomaterialia.

[20]  Sara M. Gaytan,et al.  Evaluation of Titanium Alloys Fabricated Using Rapid Prototyping Technologies—Electron Beam Melting and Laser Beam Melting , 2011, Materials.

[21]  E. Sachs,et al.  Design and fabrication of cast orthopedic implants with freeform surface textures from 3-D printed ceramic shell. , 2000, Journal of biomedical materials research.

[22]  O. Harrysson,et al.  Direct metal fabrication of titanium implants with tailored materials and mechanical properties using electron beam melting technology , 2008 .

[23]  M. Simonelli.  Microstructure evolution and mechanical properties of selective laser melted Ti-6Al-4V , 2014 .

[24]  André Luiz Jardini,et al.  Microstructure and mechanical behavior of porous Ti-6Al-4V parts obtained by selective laser melting. , 2013, Journal of the mechanical behavior of biomedical materials.

[25]  W. G. Frazier,et al.  Hot working of commercial Ti–6Al–4V with an equiaxed α–β microstructure: materials modeling considerations , 2000 .

[26]  M. Mrksich,et al.  Using electroactive substrates to pattern the attachment of two different cell populations , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[27]  Jie Jiang,et al.  Osteoblast and chondrocyte interactions during coculture on scaffolds. , 2003, IEEE engineering in medicine and biology magazine : the quarterly magazine of the Engineering in Medicine & Biology Society.

[28]  Fábio Pinto da Silva,et al.  Medical design: Direct metal laser sintering of Ti–6Al–4V , 2010 .

[29]  H. Maier,et al.  In situ characterization of the deformation and failure behavior of non-stochastic porous structures processed by selective laser melting , 2011 .

[30]  V. Sikavitsas,et al.  Biomaterials and bone mechanotransduction. , 2001, Biomaterials.

[31]  Haijun Gong,et al.  Generation and detection of defects in metallic parts fabricated by selective laser melting and electron beam melting and their effects on mechanical properties. , 2013 .

[32]  Richard A. Robb,et al.  Schwarz meets Schwann: Design and fabrication of biomorphic and durataxic tissue engineering scaffolds , 2006, Medical Image Anal..

[33]  J. Kruth,et al.  Micro-CT-based improvement of geometrical and mechanical controllability of selective laser melted Ti6Al4V porous structures , 2011 .

[34]  Takashi Nakamura,et al.  Bioactive Ti metal analogous to human cancellous bone: Fabrication by selective laser melting and chemical treatments. , 2011, Acta biomaterialia.

[35]  H. J. Rack,et al.  Phase transformations during cooling in α+β titanium alloys , 1998 .

[36]  Ahmed Hussein,et al.  Evaluations of cellular lattice structures manufactured using selective laser melting , 2012 .

[37]  Lewis Mullen,et al.  Selective Laser Melting: a regular unit cell approach for the manufacture of porous, titanium, bone in-growth constructs, suitable for orthopedic applications. , 2009, Journal of biomedical materials research. Part B, Applied biomaterials.

[38]  I. Yadroitsava,et al.  Selective laser melting of Ti6Al4V alloy for biomedical applications: Temperature monitoring and microstructural evolution , 2014 .

[39]  Klaus Mecke,et al.  Minimal surface scaffold designs for tissue engineering. , 2011, Biomaterials.

[40]  Wei Zhang,et al.  Phase transformation dynamics during welding of Ti–6Al–4V , 2004 .

[41]  大槻 文悟,et al.  Pore throat size and connectivity determine bone and tissue ingrowth into porous implants : three-dimensional micro-CT based structural analyses of porous bioactive titanium implants , 2007 .

[42]  C. V. van Blitterswijk,et al.  Porous Ti6Al4V scaffold directly fabricating by rapid prototyping: preparation and in vitro experiment. , 2006, Biomaterials.

[43]  Howard G. Hatch,et al.  INFINITE PERIODIC MINIMAL SURFACES WITHOUT SELF-INTERSECTIONS , 2002 .

[44]  J. Galante,et al.  Fiber metal composites in the fixation of skeletal prosthesis. , 1973, Journal of biomedical materials research.

[45]  Jean-Pierre Kruth,et al.  Study of laser‐sinterability of ferro‐based powders , 2005 .

[46]  D. Dunand,et al.  Solid-state foaming of titanium by superplastic expansion of argon-filled pores , 2001 .

[47]  M. Wolcott.  Cellular solids: Structure and properties , 1990 .

[48]  Christoph Leyens,et al.  Deposition of Ti–6Al–4V using laser and wire, part I: Microstructural properties of single beads , 2011 .

[49]  J. Kruth,et al.  A study of the microstructural evolution during selective laser melting of Ti–6Al–4V , 2010 .

[50]  R. Huiskes,et al.  The relationship between stress shielding and bone resorption around total hip stems and the effects of flexible materials. , 1992, Clinical orthopaedics and related research.