Coatings for Bio-corrosion, Tribo-corrosion, and Bio-tribology

Monday, April 29, 2013 10:00 AM in Room Sunrise

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10:00 AM D2-1-1 Why Does Titanium Alloy Wear Cobalt Chrome Alloy Despite Lower Bulk Hardness: a Nanoindentation Study?
Steve Bull (Newcastle University, UK); Osman Sayginer (Newcastle University, UK, Turkey); Noushin Moharrami (Newcastle University, UK)
Titanium-based and cobalt-chrome alloys have been widely used in orthopaedic applications as these materials can significantly enhance the quality of human life as implant materials. The longevity of these materials is highly influenced by their mechanical properties. In some devices cobalt chrome components articulate with titanium alloy counterfaces (e.g. in the taper connections of stems and femoral heads in modern modular designs) and damage has been reported of the harder cobalt chrome by the softer titanium alloy component. This study attempts to understand why this might occur by investigating bulk and surface mechanical properties (such as hardness and Young’s modulus) of a number of hip implants and test samples using a Hysitron triboindenter. AFM images were also obtained to determine the contact area and hence pile-up correction factors.The results were compared for samples before being used in the body, to account for surface mechanical response due to implant manufacture, and after to account for the materials response to long-term cyclic loads. To assess the effects of oxidation, the alloys were treated electrochemically with NaCl solution at body temperature. It was found that titanium oxidised preferentially compared with cobalt-chrome alloys. Furthermore, the oxidised titanium showed significantly higher hardness values therefore damaging the unoxidised cobalt-chrome material. The implications for device design and manufacture will be discussed.
10:20 AM D2-1-2 Metal - Metal Oxide Thin Film-Biological Interfaces and the Role of Bio-mechano-electro-chemical Processes
Jeremy Gilbert, Viswanathan Swaminathan, Morteza Haeri, Sachin Mali (Syracuse University, US)
Metallic Biomaterials continue to serve as the major class of materials used in a wide array of medical devices today. The primary alloy systems used come from the titanium, cobalt-chromium, and stainless steel families and are extraordinarily corrosion resistant and biocompatible with the human body. The major source of these characteristics are the nanometer-scale oxide thin films that spontaneously form on their surface. While these are known as passive films because of their ability to resist corrosion, they are not passive in their structure, properties or behavior when implanted in the biological milieu. Importantly, when these medical devices experience mechanical interactions at their surface, significant coupled processes interact to result in major changes to the surface and its properties and performance. In this presentation, the effects and consequences of mechanical abrasion of immersed oxide films on metallic substrates will be described. The coupled processes of surface mechanics with electrochemical effects will be explored in the context of the biological system. This includes explaining how oxide abrasion results in dramatically increased corrosion processes, large excursions in voltage, changes in oxide film electrical properties (impedance), altered solution chemistry and how these changes can influence the cells and proteins immediately adjacent to the implant surface. Large cathodic voltage excursions are possible and these shifts lower surface impedance characteristics and result in significant alteration in adsorbed protein conformation and behavior, and induce an apoptotic cell death in-vitro that may have a significant clinical effect on implant performance. Test methods for the exploration of fretting crevice corrosion will be described for both material surface studies and implant studies.
11:00 AM D2-1-4 Dominant Role of Molybdenum in the Electrochemical Deposition of Biological Macromolecules on Metallic Surfaces
Elizabeth Martin (Northwestern University, US); Robin Pourzal, Mathew Mathew (Rush University Medical Center, US); Kenneth Shull (Northwestern University, US)

The corrosion of CoCrMo, an alloy frequently used in orthopedic implants, was studied with an electrochemical quartz crystal microbalance (QCM) in three physiologically relevant solutions. Mass changes were measured during potentiodynamic tests, showing material deposition in protein solutions at potential levels that caused mass loss when the proteins were not present. X-ray photoelectron spectroscopy (XPS) data indicated that the deposited material was primarily organic, and therefore was most likely derived from proteins in the electrolyte. Material deposition consistently occurred at a critical potential and was not dependent on the current density or total charge released into solution. Corrosion studies on pure Co, Cr and Mo in protein solutions only found material deposition on Mo. We hypothesize that organic deposition results from the interaction of Mo(VI) with proteins in the surrounding solution. The organic layer is reminiscent of tribochemical reaction layers that form on the surface of CoCrMo hip bearings, suggesting that these types of layers can be formed by purely electrochemical means.

11:20 AM D2-1-5 Engineering Nanostructured Cubic Zirconia Coating for Enhanced Biointegration of Orthopaedic Implants
Fereydoon Namavar (University of Nebraska Medical Center, US); Renat Sabirianov (University of Nebraska at Omaha, US); Alexander Rubenstein, Raheleh Miralami, GeoffreyM. Thiele, J.Graham Sharp, KevinL. Garvin (University of Nebraska Medical Center, US)
Failure of osseointegration prevents long-term stability, which results in pain, implant loosening, and infection, all of which can necessitate revision replacement surgery. Hydroxyapatite (HA) and bioactive glasses have been studied for decades because of their bioactive properties. However, concerns have been raised about the bioabsorption of the HA layer, the mechanical strength of the HA layer [1, 2], and the HA layer debonding from the metal implant [2, 3]. We designed and produced nanostructurally stabilized pure cubic zirconia ceramic [4] coatings by an ion beam assisted deposition (IBAD) with nanostructures comparable to the size of adhesive proteins (with 2-25 nm grain size). Our ceramic coatings exhibit high hardness (16±1.7 GPa) and a zero contact angle with serum and possess excellent adhesion to all orthopaedic materials. Adhesion and proliferation experiments were performed with a mesenchymal stromal cell cell line (OMA-AD) on the nano-structured coatings and compared to Cobalt Chrome, Titanium, and HA. Our results with Alamar blue, direct cell counting, and scanning electron microscopy, clearly indicated that nano-engineered cubic zirconia is superior in supporting growth, adhesion, and proliferation. Further adhesion experiments with fibronectin (FN) from human plasma using an ELISA based technique resulted in higher FN adsorption on nanoengineered surfaces as compared to other conventional orthopedic materials. These experiments indicate a clear correlation between cell and FN adhesion. Since the absorption of adhesive proteins such as FN is a key factor in cell adhesion and bone formation at an implant surface, we are proposing a phenomenological concept based on electrostatic and steric complementarity that may explain the enhanced adhesion of cells, through modification of adhesive protein absorption, to the engineered nanostructured surfaces as compared to conventional smooth surfaces [5]. 1. A. El-Ghannam, Expert Review Medical Devices, 2 (1), 87-101, 1340-1347 (2005). 2. B.D. Ratner, Journal of Dental Education, 65 (12), 340-1347 (2001). 3. O. Reikeras, R.B.Gunderson, Acta Orthop Scand. 73 (1), 104-108 (2002). 4. F. Namavar, C.L. Cheung, R.F. Sabirianov, et. al, Nano Lett., 8, 988 (2008). 5. R.F. Sabirianov, A. Rubinstein, F. Namavar, Phys. Chem. Chem. Phys. 13, 6597, (2011).