Discerning in-vivo corrosion mechanisms and failure modes of explanted prostheses Part I By Norman Munroe, Vishal Musaramthota, Christopher Emerson and Kinzy Jones Introduction Orthopedic implants have seen a major increase in usage within the US and worldwide. Three decades ago, the average age for a hip replacement was 78 years, while today it is 59 years. The American Academy of Orthopedic Surgeons notes that more than 700,000 primary total hip or knee replacements were performed in the US, with demand doubling in the next decade. However, increased usage has been accompanied by an increase in revision, where the prosthesis is removed. Most joint replacements have been performed primarily on older patients and as such, there is a dearth of information on how these implants would hold up in younger patients over longer periods of time. Despite the advent of new designs and advanced materials, orthopedic surgeons are still concerned that younger knee replacement patients, for example, may need to have replacement in as little as 5 to 10 years, which leads to bone loss every time the surgery is performed. Figure 1: (a) Diseased hip before and after artificial hip joint implantation [1]; (b) artificial knee joint coated with various Medthin coatings from Ionbond that prevent corrosion, minimize wear, offer excellent load carrying capacity and greatly reduce metallic ion concentrations [2]; (c) from left to right, medialposterior aspect of the a tapered stem region (left) and the inner medial (middle) and lateral halves (right) of the cut sleeve [3].
Significance There has been an increase in the recall of prosthetic devices (Zimmer 11,658 in 2015 and DePuy 40,000 in 2011) based on increased failure rates due to materials defects or construction technology. The FDA in 2015 indicated that tribological interactions (metal on metal) of implants provide a unique risk due to the deleterious effect of metallic debris on surrounding tissues. This research is focused on utilizing a group of explanted hip prostheses of known medical history and develop protocols, from which information can be garnered on microstructure, fretting/crevice corrosion, failure analysis and their manifestations in product design. Previous research The following table summarizes some of our previous/current investigations on the biocompatibility of Ti alloys and Mg based biodegradable alloys used for the manufacture of prosthetic and cardiovascular devices. The following alloys are investigated: titanium alloys (NiTi-X, Ti-Ta and Porous Nitinol (PNT)); biodegradable magnesium alloys (Mg- Zn-X); and metal matrix composites (MMC). Table 1: Summary of previous investigations on bio-implant materials Alloy Ti-Ta-X PNT Mg-Zn-X (Biodegradable) Manufacturing Techniques Reference of Articles Published Industrial/University Collaborators Powder Metallurgy, [4], [5] Dynamite ARC Melting Technology; National Institute of Standarts and Technology (NIST); Electrobright Self-propagating [6], [7], [8], [9], Biothrex; high-temperature [10], [11], [12] Electrobright synthesis Casting [13], [24], [27] ACI Alloys, Inc.; Electrobright; Brunel University, London
Alloy Manufacturing Techniques Reference of Articles Published Industrial/University Collaborators NiTi-X ARC Melting [14], [15], [16], [17], [18], [19], [20], [23], [25], [26] National Institute of Standards and Technology (NIST); Electrobright NiTi-CNT Powder Metallurgy [21], [22] Fraunhofer Institute, Germany The results of cyclic polarization corrosion studies on electropolished (EP), magnetoelectropolished (MEP) and porous Nitinol (PNT) are summarized in fig. 2a; potentiodynamic polarization studies on Mg alloys are illustrated in fig. 2b; and EIS polarization resistance due to the growth of osteoblast cells on TiTa alloy are shown in fig. 2c. Figure 2: (a) Cyclic polarization scan, where Eb Break down potential, Er Rest potential, Subscripts: 1- Untreated PNT, 2- MEP PNT, 3- EP PNT; (b) Potentiodynamic scan; (c) Observation of growth of osteoblast cells on TiTa after inoculation by EIS. Fig. 3 (a) illustrates the cytotoxicity of surface treated PNT corrosion products on human osteoblast cells and fig. 3 (b) shows osteoblast cell growth on the surface of various biomaterials.
Figure 3: (a) Cytotoxicity of leached ions during corrosion on human osteoblast cells by SRB assays; (b) Osteoblast cell growth observed on different implant materials Fig. 4 illustrates X-ray photoelectron spectroscopy (XPS) analysis to evaluate the surface chemistry of PNT; fig. 4 (a) shows the presence of a passivating titanium oxide surface layer that is void of any nickel oxide. The elemental depth profile and binding energy of atomic species are shown in fig. 4 (b and c). Figure 4: PNT: (a) Montage plots of surface Ni and Ti; (b) Elemental depth profile; (c) Binding energy and relative abundance of atomic species Current Research In this investigation, 48 CoCrMo explanted arthroplasty samples were provided by Dr. Carlos Lavernia, Head of Mercy Hospitals Orthopedic Institute. Although the medical history of the explanted prostheses have been documented under strict confidentiality, the processing history of the materials of construction was unknown. Additionally, different design features of varying dimensions are known to introduce microstructural heterogeneity resulting in unpredictable electrochemical, tribological and osseointegration properties. However, discussions on influential factors such as material processing, the resulting microstructure, design of the prostheses, length of implantation as they relate to the appearance of the samples, and the extent to which wear debris is generated at the stem-sleeve interface will be described in future publications.
A micro corrosion cell shown in fig. 5a was employed to conduct corrosion tests on as-cast CoCrMo alloy (AC), low carbon wrought (LCW) CoCrMo alloy and high carbon wrought (HCW) CoCrMo alloy (the composition and types of alloy were ascertained by conducting SEM/EDS analyses and comparing the results with those in the literature). Potentiodynamic polarization tests were conducted in accordance with ASTM F2129-08 using a Gamry three electrode system where the reference electrode was Ag/AgCl, counter electrode was carbon and the working electrode was the metal sample. Fig. 5b shows a sectioned sample cut from an explanted prosthetic stem illustrating evidence of in-vivo corrosion. Figure 5: (a) Micro corrosion cell assembly; and (b) Sample section from an explanted prosthetic stem. Results Severe corrosion/fretting was observed in 100% of AC; 24% of LCW; and 9% of HCW alloys. In-vitro potentiodynamic polarization tests in Hanks solution revealed that the AC alloy had the highest Ecorr value relative to LCW and HCW; however, relatively similar icorr values were obtained. With a variation of one order of magnitude in exchange current density (fig. 6a), a change of potential in the transpassive domain is evaluated. This is of great importance for an alloy, as it provides an estimation as to how the width of the passivation domain varies as shown in fig. 6b. The size of the passivation domain ranged in the following order: LCW > HCW > AC but the visual display of corroded surfaces ranged in the following order: HCW < LCW < AC. LCW possessed a homogeneous microstructure with a chromium rich passive oxide film, whereas HCW was inhomogeneous due to chromium carbide formation resulting in chromium depleted zones, thereby making it relatively more prone to pitting corrosion.
Conclusions Different processing techniques resulted in microstructures that influence the electrochemical behavior of CoCrMo alloys. LCW alloys were the least prone to corrosion due to a more homogeneous microstructure and a uniform passive oxide film, whereas Figure 6: (a) Typical potentiodynamic polarization graph for CoCrMo alloy, (b) Overlay of the electrochemical behavior of the low carbon wrought, as-cast, and high carbon wrought alloys HCW alloy was inhomogeneous due to chromium carbide formation and thus, marginally more prone to corrosion as evidenced by the widths of the both passive domains. Although the AC alloy had the highest corrosion potential (a thermodynamic property), 100% of the samples displayed evidence of corrosion. This is corroborated by the fact that AC also displayed the smallest passivating width. Although CoCrMo has been readily available as an orthopedic alloy since the 1930s, its future usage for prosthetic applications is controversial. One limitation of studying explanted prostheses is that the implant materials were manufactured more than a decade ago which imposes difficulties when comparing them to new generation materials. Recently, there has been a shift towards the usage of ceramic materials for femoral head components. Acknowledgments The authors would like to thank Dr. Carlos Lavernia for providing explanted hip prostheses."
References 1. Study on Total Hip Replacement by Dr. Justin Lareau, Source: http://justinlareaumd.com/hip-anatomy/treatments/total-hipreplacement-procedure/, 2015. 2. Medthin Coating Portfolio from Ionbond, Source: http://www.ionbond.com/en/coatingservices/medical/coating-portfolio/ medthintm-20-facts/ accessed on July 10, 2015. 3. Christian R. Fraitzl, Luis E. Moya, Lorenzo Castellani, Timothy M. Wrigh, Robert L. Buly, Corrosion at the Stem-Sleeve Interface of a Modular Titanium Alloy Femoral Component as a Reason for Impaired Disengagement, The Journal of Arthroplasty, 26 (1), 2011, pp 113-119. 4. P. K. S. Gill, N. Munroe, C. Pulletikurthi, S. Pandya, W. Haider, Effect of Manufacturing Process on the Biocompatibility and Mechanical Properties of Ti-30Ta Alloy. Journal of Materials Engineering and Performance. DOI: 10.1007/s11665-011-9874-7 5. P. K. S. Gill, N. Munroe, C. Pulletikurthi, S. Pandya, V. Tek, W. Haider, In-Vitro Localized Corrosion Studies of Ti-Ta Alloy, SMST 2010 The International Conference for Shape Memory and Superelastic Technologies, May 16-20, 2010, Pacific Grove, California. 6. N. Munroe, C. Pulletikurthi, W. Haider, Enhanced Biocompatibility of Porous Nitinol, J Mater Eng Perform, 18 (5-6), 2009, p 765-767. 7. C. Pulletikurthi, N. Munroe, P. K. S. Gill, S. Pandya, D. Persaud, K. Iyer, W. Haider, Cytotoxicty of Ni from Surface Treated Porous Nitinol (PNT) on Osteoblast Cells, Journal of Materials and Performance. 8. C. Pulletikurthi, N. Munroe, W. Haider, V. Tek, P. K. S Gill and S. Pandya, The Effect of Electropolishing and Magnetoelectropolishing on the Biocompatibility of Porous Nitinol Implant, Biointerface, October 26-28, 2009, San Mateo, California. 9. C. Pulletikurthi, N. D. Munroe, W. Haider, P. K. S. Gill, S. Pandya, V. 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Munroe, S. Pandya, P.S. Gill, and C. Pulletikurthi, Assessing the Effect of Surface Roughness on Corrosion Resistance of Ternary Nitinol Alloys. MS&T, October 17-21, 2010, Houston, Texas. 19. W. Haider, N. Munroe, V. Tek, Y. Tang, A. J. Mc Goron C. Pulletikurthi, P. K. Singh Gill, S. Pandya, Comparing the Biocompatibility of Electropolished and Magnetoelectropolished Nitinol, Biointerface, October 26-28, 2009, San Mateo, California. 20. W. Haider, N. Munroe, Y. Tang, A. J. Mc Goron, C. Pulletikurthi, P. K. S. Gill, S. Pandya, Endothelialization of Ternary Nitinol Alloys, Materials and Processes for medical devices-conference and Exhibition, August 10-12, 2009, Minneapolis, Minnesota. 21. P. K. S. Gill, N. D. Munroe, W. Haider, C. Pulletikurthi, S. Pandya, V. Tek, Biocompatibility Assessment of a Conductive Ni-Ti-CNT Composite, MRS Fall Meeting, November 30 - December 4, 2009, Boston, Massachusetts. 22. P. Gill, N. Munroe, C. Pulletikurthi, Investigating Carbon Nanotubes in Copper-Chromium Metal Matrix Composite, Journal of Materials Engineering and Performance, 2012. DOI: 10.1007/s11665-012-0198-z. 23. R. Rokicki, T. Hryniewicz, C. Pulletikurthi, N. Munroe, K. Rokosz, Towards a Better Corrosion Resistance and Biocompatibility Improvement of Nitinol Medical Devices, JMEPEG DOI: 10.1007/s11665-015-1429-x. 24. P. Gill, N. Munroe and A. Datye, Assessing the Effect of Surface Roughness on Corrosion Behavior of Magnesium Alloys, Journal of Industrial and Engineering Chemistry, In press. 25. P. Gill, V. Musaramthota, N. Munroe, A. Datye, R. Dua, W. Haider, R. Rokicki and A. McGoron, Surface Modification of Ni-Ti Alloys for Stent Application after Magnetoelectropolishing, Materials Science and Engineering C, pp:37-44, 50 (1), 2015. 26. C. Pulletikurthi, N. Munroe, M. Dugrot, W. Haider, S. Amruthaluri, D. Stewart, S. 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Manuscript JBMR-B-14-0111.R3. 27. P. Gill, N. Munroe, A. Datye, Synthesis, Characterization and Mechanical Properties of Magnesium Based Biodegradable Alloys. Emerging Materials Research, 2013. 10.1680/emr.12.00020. 28. P. Gill, N. Munroe and A McGoron, Characterization and Degradation Behavior of Anodized Magnesium-Hydroxyapatite Metal Matrix Composites, Journal of Biomimetics, Biomaterials, and Tissue Engineering, 2012, 16, 55-69. 10.4028 / www.scientific.net/ JBBTE.16.55. 29. D. Persaud-Sharma, N. Munroe and A. McGoron, Electro and Magneto-Electropolished Surface Micro-Patterning on Binary and Ternary Nitinol, Trends Biomater Artif Organs. 26 (2) 74-85, 2012.