This paper presents some examples of knee and hip implant components containing porous structures and fabricated in monolithic forms utilizing electron beam melting (EBM). In addition, utilizing stiffness or relative stiffness versus relative density design plots for open-cellular structures (mesh and foam components) of Ti-6Al-4V and Co-29Cr-6Mo alloy fabricated by EBM, it is demonstrated that stiffness-compatible implants can be fabricated for optimal stress shielding for bone regimes as well as bone cell ingrowth. Implications for the fabrication of patient-specific, monolithic, multifunctional orthopaedic implants using EBM are described along with microstructures and mechanical properties characteristic of both Ti-6Al-4V and Co-29Cr-6Mo alloy prototypes, including both solid and open-cellular prototypes manufactured by additive manufacturing (AM) using EBM. 1. Introduction Although Ti and its alloys have been used for more than half a century as monolithic, solid implant materials, they are limited by lack of fusion and bone resorption due to stress shielding. This results from an order-of-magnitude greater metal stiffness (or Young’s modulus) relative to cortical (hard) bone and up to two orders of magnitude for cancellous (or trabecular), soft bone [1–3]. Wear debris production for contacting surfaces and the elimination of necessary vascularization are also often attendant issues [4]. However, the presence of a nonporous, stable passive film (TiO2) on the surface minimizes the diffusion of metal ions from the bulk material and prevents corrosion of the material in contact with human tissues [2]. Other metallic alloys such as stainless steel (316L) and Co-Cr (or Co-Cr-Mo) alloys are also used, especially in preference to Ti alloys for load-bearing applications due to limited strength or poor fatigue properties, and critical wear applications. These alloys also rely on the presence of chromium for their corrosion resistance. However, breakdown of passivating layers, variations in the physiological environment, including infection, can increase corrosion or corrosion rate as well as corrosion products. Consequently, biocompatibility in its broadest sense is a complex issue [1, 2, 5]. While conventional orthopaedic knee and hip implants in particular, fixed with acrylic cement, have produced excellent results in older patients, less success is generally achieved for younger, more active individuals [7]. As alternatives to acrylic cement as well as other benefits promoting biocompatibility, porous scaffolds have exhibited considerable potential
References
[1]
J. D. Bronzino, Ed., The Biomedical Engineering Handbook, vol. 1, CRC Press, Boca Raton, Fla, USA, 2000.
[2]
P. Christel, A. Meunier, and A. J. C. Lee, Eds., Biological and Biomechanical Performance of Biomaterials, Elsevier, New York, NY, USA, 1986.
[3]
S. Yang, K. F. Leong, Z. Du, and C. K. Chua, “The design of scaffolds for use in tissue engineering. Part I. Traditional factors,” Tissue Engineering, vol. 7, no. 6, pp. 679–689, 2001.
[4]
J. R. Cahoon, “On the corrosion products of orthopedic implants,” Journal of Biomedical Materials Research, vol. 7, no. 4, pp. 375–383, 1973.
[5]
G. Ryan, A. Pandit, and D. P. Apatsidis, “Fabrication methods of porous metals for use in orthopaedic applications,” Biomaterials, vol. 27, no. 13, pp. 2651–2670, 2006.
[6]
L. E. Murr, K. N. Amato, S. J. Li et al., “Microstructure and mechanical properties of open-cellular biomaterials prototypes for total knee replacement implants fabricated by electron beam melting,” Journal of the Mechanical Behavior of Biomedical Materials, vol. 4, no. 7, pp. 1396–1411, 2011.
[7]
R. D. Beckenbaugh and D. M. Ilstrup, “Total hip arthroplasty. A review of three hundred and thirty-three cases with long follow-up,” Journal of Bone and Joint Surgery—Series A, vol. 60, no. 3, pp. 306–313, 1978.
[8]
D. C. Dunand, “Processing of titanium foams,” Advanced Engineering Materials, vol. 6, no. 6, pp. 369–376, 2004.
[9]
R. Singh, P. D. Lee, R. J. Dashwood, and T. C. Lindley, “Titanium foams for biomedical applications: a review,” Materials Technology, vol. 25, no. 3-4, pp. 127–136, 2010.
[10]
O. L. A. Harrysson, O. Cansizoglu, D. J. Marcellin-Little, D. R. Cormier, and H. A. West II, “Direct metal fabrication of titanium implants with tailored materials and mechanical properties using electron beam melting technology,” Materials Science and Engineering C, vol. 28, no. 3, pp. 366–373, 2008.
[11]
P. Heinl, L. Müller, C. K？rner, R. F. Singer, and F. A. Müller, “Cellular Ti-6Al-4V structures with interconnected macro porosity for bone implants fabricated by selective electron beam melting,” Acta Biomaterialia, vol. 4, no. 5, pp. 1536–1544, 2008.
[12]
X. Li, C. Wang, W. Zhang, and Y. Li, “Fabrication and characterization of porous Ti6Al4V parts for biomedical applications using electron beam melting process,” Materials Letters, vol. 63, no. 3-4, pp. 403–405, 2009.
[13]
L. E. Murr, S. M. Gaytan, F. Medina et al., “Next-generation biomedical implants using additive manufacturing of complex cellular and functional mesh arrays,” Philosophical Transactions of the Royal Society A, vol. 368, no. 1917, pp. 1999–2032, 2010.
[14]
L. J. Gibson and M. F. Ashby, Cellular Solids: Structure and Properties, Cambridge University Press, New York, NY, USA, 1997.
[15]
M. F. Ashby, A. Evans, N. A. Fleck, L. J. Gibson, J. W. Hutchinson, and H. N. G. Wadley, Metal Foams: A Design Guide, Butterworth-Heinemann, Boston, Mass, USA, 2000.
[16]
D. A. Ramirez, L. E. Murr, S. J. Li et al., “Open-cellular copper structures fabricated by additive manufacturing using electron beam melting,” Materials Science and Engineering A, vol. 528, no. 16-17, pp. 5379–5386, 2011.
[17]
L. E. Murr, S. J. Li, Y. X. Tian, K. Amato, E. Martinez, and F. Medina, “Open-Cellular Co-based and Ni-base superalloys fabricated by electron beam melting,” Materials, vol. 4, no. 4, pp. 782–790, 2011.
[18]
G. Roebben, B. Bollen, A. Brebels, J. Van Humbeeck, and O. Van Der Biest, “Impulse excitation apparatus to measure resonant frequencies, elastic moduli, and internal friction at room and high temperature,” Review of Scientific Instruments, vol. 68, no. 12, pp. 4511–4515, 1997.
[19]
L. E. Murr, S. A. Quinones, S. M. Gaytan et al., “Microstructure and mechanical behavior of Ti-6Al-4V produced by rapid-layer manufacturing, for biomedical applications,” Journal of the Mechanical Behavior of Biomedical Materials, vol. 2, no. 1, pp. 20–32, 2009.
[20]
L. Thijs, F. Verhaeghe, T. Craeghs, J. V. Humbeeck, and J. P. Kruth, “A study of the microstructural evolution during selective laser melting of Ti-6Al-4V,” Acta Materialia, vol. 58, no. 9, pp. 3303–3312, 2010.
[21]
S. M. Gaytan, L. E. Murr, E. Martinez et al., “Comparison of microstructures and mechanical properties for solid and mesh cobalt-base alloy prototypes fabricated by electron beam melting,” Metallurgical and Materials Transactions A, vol. 41, no. 12, pp. 3216–3227, 2010.
[22]
O. L. A. Harrysson and D. R. Cormier, “Direct fabrication of custom orthopaedic implants using electron beam melting technology,” in Advanced Manufacturing Technology for Medical Applications: Reverse Engineering, Software Conversion, and Rapid Prototyping, I. Gibson, Ed., chapter 9, John Wiley & Sons, Chichester, UK, 2006.
