ICMCTF2013 Session D2-2: Coatings for Bio-corrosion, Tribo-corrosion, and Bio-tribology

Monday, April 29, 2013 1:30 PM in Room Sunrise

Monday Afternoon

Time Period MoA Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2013 Schedule

Start Invited? Item
1:30 PM D2-2-1 Evaluation of the Bio-tribocorrosion Processes of Colonized Ti6Al4V Implants in Presence of Organic and Cellular Material
Maria Runa (University of Minho, Portugal); Mathew Mathew (Rush University Medical Center, US); Maria Fernandes (University of Porto, Portugal); Luis Rocha (University of Minho, Portugal)

In uncemented Ti-based implants, the tribochemical reactions occurring at the implant/bone interface were reported to be caused by a combined effect of mechanical load and a complex chemical-biological environment. These reactions are due to micromotion occurring at the implant/bone interface from daily activities of the patients, and they can lead to tissue inflammation, crack initiation and early fracture of the implant. The interplay between chemical-biological-mechanical parameters and in particular the influence of relevant proteins and osteoblastic cells, on the material degradation is of extreme clinical relevance and needs to be clarified.

The aim of this work is to evaluate the bio-tribocorrosion mechanisms of etched Ti6Al4V alloys colonized with MG63 osteoblastic-like cells. The colonized materials and control groups were characterized through cell viability/proliferation and alkaline phosphatase activity. Tribocorrosion tests were performed under a reciprocating sliding configuration at different electrochemical potentials (-0.1V and +0.5V/SCE), using a simulated body fluid and the culture medium as the electrolyte. An alumina ball was used as counterbody. Normal loads between 0.05N and 1N, were applied (153MPa and 415MPa initial contact Hertzian pressure) which allowed more detailed information on the destruction pathways of the top surface layers of the material (adsorbed proteins, passive film, etc.) to be followed. All tests were performed at a controlled temperature of 37ºC.

The results obtained demonstrated the capability of the oxide film to re-grow (repassivation) after mechanical damage. The electrochemical behavior of the alloy was shown to depend on the stage of the passive film formed on top of the material. The interaction of biological material, present in the simulated body fluid, with the surface of the Ti6Al4V alloy was found to improve the resistance of the passive layer. The total weight loss (Kwc) and synergistic ratio between chemical and mechanical wear loss (Kc/Kw) were estimated to identify the mechanistic transitions in the wear-corrosion process, which ranged from 0.4 to 3.5, depending on the stage of the passive film. Also, the materials colonized with osteoblastic-like cells showed an important influence on the chemical and tribological response of this alloys, leading to valuable findings for long-term metallic implant applications.
1:50 PM D2-2-2 Tribocorrosion Evaluation of nc-TiN/a-Si3N4 Deposited on Ti6Al4V in Sliding Contact in Physiological Saline Solution
Jose Garcia, Martin Flores (Universidad de Guadalajara, Mexico); Omar Jimenez (Universidad de Guadadalajara, Mexico); Eduardo Andrade (Universidad Nacional Autónoma de México, Mexico)

Several studies have been carried out using nc-TiN/a-Si3N4 deposited on Ti6Al4V substrates using DC and RF reactive dual magnetron sputtering in order to understand the behavior of this material when applied in human joint replacement. Characterization, mechanical and corrosive tests were conducted, including: XRD, XPS and RBS techniques to analyze the structure and composition of coatings, profilometry to analyze the topography of substrate, coating and wore Surfaces, scratch test to evaluate film adhesion and electrochemical technique as well as a reciprocating tribocorrosion test in physiological saline solution, to evaluate the corrosion susceptibility under static and reciprocating conditions respectively. All the results are analyzed and discussed.

2:10 PM D2-2-3 Nanotube Surface Modifications For Biomedical Applications
Tolou Shokuhfar (Michigan Technological University, US)

Engineered-nanotubular structures offer exciting progress toward the design of multifunctional medical implants. To bring this to reality, the mechanical, physical, biocompatibility, and interfacial properties of such structures should be optimized. The mechanics of nanotubes is important from mechanotransduction points of view. We have observed that the fabrication of TiO2 nanotubes with elastic modulus close to actual bone promotes osteoblast growth. In order to investigate the effect of nanotubes on behavior of osteoblast cells, series of novel experiments on measuring the mechanical properties of individual TiO2 nanotubes followed by in-vitro cell culture tests were conducted. The nanotubes were tested in the chamber of transmission electron microscope using an in-situ atomic force microscopy stage with force resolutions better than 1 nN. Thin and thick nanotubes were tested to check if there are variations of mechanical properties as a function of size. It was shown that the nanotubular characteristics of the surface improve cell proliferation, attachment and spreading of osteoblast cells. We have developed a novel cell/surface interfacial characteristic method using focused ion beam milling (FIB) and scanning transmission electron microscopy (SEM) techniques. With this novel approach it was possible to cut through sections of cells and the underlying substrate and directly observe the biophysical interactions of osteoblasts with TiO2 nanotubes. The results of this approach show a tight interface where TiO2 nanotubes act as anchoring sites for osteoblasts to attach and even grow inside the hollow section of nanotubes. This tight interaction would eventually result in enhance bon-implant interlock. Based on these findings, it is possible to speculated that surface modification of Ti implants by a TiO2 nanotube layer with elastic behavior close to the actual bone can be promising to overcome stress-shielding, a common reason for implant failures.

2:50 PM D2-2-5 Predicting Thickness of Passive Films in Order to Prevent Degradations of Implants
Jean Geringer (Ecole Nationale Superieure des Mines, France); Matthew Taylor, Digby Macdonald (Penn State University, US)

Every year, one in every 30 Americans has a hip prosthesis implanted, i.e. 250,000 every year implants in the US market. Health issues with regard to patient mobility, which in turn reflects an aging population, are of increasing concern,but we also see a trend toward younger and younger patients. Younger, first time recipients of hip prostheses are of concern, because of the high probability that they will be recipients of multiple prostheses replacements over their lifetimes, since some implants have approximate lifetimes of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel, in order to optimize lifetime. Fretting corrosion, friction under small displacements, between stainless steel and bone, for instance, occurs during human gait, due to repeated loadings and un-loadings,. Some experimental investigations of fretting corrosion have been reported. As is well known, metallic alloys and especially stainless steels are covered with a passive film that inhibits corrosion and hence degradation when implanted within the body. This passive layer of few nanometers in thickness at ambient temperature, is the key of our reactive metals-based civilization according to some authors. This work is dedicated to predicting the passive layer thicknesses of stainless steel under fretting corrosion conditions, with specific emphasis on the role of proteins. The analysis is based on the Point Defect Model (PDM, micro scale) and an update of the model on the friction process (micro-macro scale) to yield the Fretting Model (FM). A genetic algorithm was used to optimize the fretting model on the experimental data, in order to derive values for important model parameters. The major results are, as expected from experimental results, albumin inhibits corrosive degradation of the steel; an incubation time is necessary for degradation of the passive film; under fretting corrosion and in the presence of a high concentration of chloride ion, passivity of the steel is also inhibited. These factors are identified as those that determine the ultimate lifetime of the prosthesis.

3:10 PM D2-2-6 Electrochemical Behavior of Esthetic Dental Coatings Tested in Sodium Chloride Solution and Artificial Saliva
Christina Pecnik, Daniel Muff, Ralph Spolenak (ETH Zurich, Laboratory for Nanometallurgy, Switzerland)

Commercially pure titanium and titanium alloys are predominantly used for dental implants, since these materials have excellent physical and chemical properties [1]. However, in certain cases a gray discoloration of the soft tissue can be observed using titanium implants, resulting in an undesired esthetic outcome [2, 3]. Therefore, a new coating system which combines the mechanical properties of metals with the good optical properties of ceramics would enhance the esthetics of dental implants. Above all, clinical success of dental implant systems depends strongly on their reliability. The coating should not only be esthetically pleasing and mechanically durable, but it should also withstand the corrosive environment below soft tissue.

In this study, ceramic and metallic thin films were deposited on commercially pure titanium substrates by reactive sputtering. Their color is formed by light interference phenomena. In order to characterize the corrosion properties of these systems, electrochemical impedance spectroscopy and potentiodynamic measurements were carried out using a three-electrode setup. Four coating systems (n = 3) were tested in 0.9 wt% NaCl solution and in artificial saliva (modified recipe of Fusayama et al. [4]) under different pH and temperature conditions. After the measurements, the samples were examined using a scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) detector.

The roughness of the substrate not only influences the color of the investigated samples here, but also their corrosion behavior. Special focus has been given to the corrosion resistance of samples immersed in artificial saliva in order to establish a life-time model for the future application.

References

1. Albrektsson, T., et al., Acta Orthopaedica Scandinavica, 1981. (2): p. 155-170.

2. Park, S.E., et al., Clinical Oral Implants Research, 2007. (5): p. 569-574.

3. Zembic, A., et al., Clinical Oral Implants Research, 2009. (8): p. 802-808.

4. Fusayama, T., S. Nomoto, and T. Katayori, Journal of Dental Research, 1963. (5): p. 1183-1197.

3:30 PM D2-2-7 Submicroporous Ta2O5 Coating Enhanced the Initial Biological Responses to Ti Surface
Ying-Sui Sun, Her-Hsiung Huang (National Yang-Ming University, Taiwan)

An amorphous tantalum pentoxide (Ta2O5) coating with submicroporous topography was prepared on titanium (Ti) using a simple hydrolysis-condensation process at room temperature to enhance the initial biological responses to Ti. Surface characteristics of the test specimens were analyzed using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, glancing angle X-ray diffractometry, field emission scanning electron microscopy and t ransmission electron microscopy . The corrosion resistance was evaluated by 5-day ion release measurement in simulated blood plasma (SBP). The cytotoxicity of the materials was determined according to ISO 10993-5 specification. The biological responses, including initial fibronectin adsorption and human bone marrow mesenchymal stem cells responses, were evaluated. Results showed that the non-cytotoxic amorphous Ta2O5 coating with submicroporous topography was deposited on the Ti surface using a simple hydrolysis-condensation process. This Ta2O5 layer significantly decreased the ion release from Ti surface in SBP, and enhanced the initial fibronectin adsorption and cell proliferation. We conclude that the presence of an amorphous Ta2O5 coating with submicroporous topography on the Ti surface decreased the ion release and enhanced initial biological responses.

3:50 PM D2-2-8 Scanning Electrochemical Microscopy (SECM) Investigation of Tribolayer Formation on a MoM Hip Implant
Joshua Meyer (Chicago State University, US); Chris Nagelli, Mathew Mathew, Markus Wimmer, Joshua Jacobs (Rush University Medical Center, US); Robert LeSuer (Chicago State University, US)
Currently metal-on-metal (MoM) hip implants are facing serious challenges. Corrosion remains one of the major concerns that limit biocompatibility and longevity of metals employed for the joint prostheses. It can lead to implant weakening from release of metal debris causing damage to cells, tissues, and host organs, eliciting potentially dangerous immune and inflammatory responses. Many electrochemical methods are available to monitor and measure the corrosion processes, however each one has its own specific application and limitations. Recent studies reported the presence of metallo-organic mixture in the form of a film or layer at the contact zone of the metal joints. The mechanical and chemical beneficial factors of such tribolayer were also reported. However, the non homogeneous structure and distribution of the layer presents problems when trying to improve the performance of the hip implant system.

In this study, scanning electrochemical microscopy (SECM) is employed to indentify the reactivity of tribolayer coated surfaces, providing insight into the corrosion protection provided by the thin film. The substrate used in this work is a low-carbon (LC) CoCrMo alloy under two different surface conditions: (1) Polished- new implant surface and (2) tribolayer coated surfaced-retrieved implant surface.

The obtained SECM images indicate that the mechanically polished surface is heterogeneous with needle-like features (50 x 10 µm) displaying increased electrochemical activity and kinetics. The presence of the tribolayer provides some corrosion resistance although there appears to be some residual surface activity possibly due to incomplete surface coverage. The knowledge about the distribution of tribolayer is essential to determine the efficiency of the tribolayer formation on implant surface. Further studies are required to generate a clear understanding the underlying mechanisms that promote the tribolayer formation

4:10 PM D2-2-9 Enhancements in Corrosion Resistance and Biocompatibility of Biomedical Ti-25Nb-25Zr Alloy Using Electrochemical Anodization Treatment
Her-Hsiung Huang, Chia-Ping Wu (National Yang-Ming University, Taiwan); Tzu-Hsin Lee (Chung Shan Medical University, Taiwan)
The biocompatibility of an implant material is determined by its surface characteristics. This study investigated the application of a fast and simple electrochemical anodization surface treatment to improve both the corrosion resistance and biocompatibility of β-type Ti-25Nb-25Zr alloy with lower elastic modulus for implant applications. The electrochemical anodization treatment produced a thin (< 100 nm) oxide layer with nanoscale porosity (pore size < 50 nm) on the Ti-25Nb-25Zr alloy surface. The surface topography and microstructure of Ti-25Nb-25Zr alloy were analyzed. The corrosion resistance was investigated using potentiodynamic polarization curve measurements in simulated body fluid (SBF). The cell adhesion and proliferation of human bone marrow mesenchymal stem cells on test specimens were evaluated using various biological analysis techniques. Results showed that the presence of a nanoporous oxide layer on the anodized Ti-25Nb-25Zr alloy surface increased the corrosion resistance (i.e., decreased both the corrosion rate and the passive current) in SBF solution compared with the untreated Ti-25Nb-25Zr alloy. Surface nanotopography enhanced the cell adhesion and proliferation on the anodized Ti-25Nb-25Zr alloy. We conclude that a fast and simple electrochemical anodization surface treatment improves the corrosion resistance and biocompatibility of β-type Ti-25Nb-25Zr alloy with lower elastic modulus for implant applications.
4:30 PM D2-2-10 Anti-fish Bacterial Pathogen Effect of Immobilized TiO2/Fe3O4 Powder on Glass
TaChih Cheng (National Pingtung University of Science and Technology, Taiwan, Taiwan, Republic of China); Ying-Chieh Lee (National Pingtung Univeristy of Science and Technology, Taiwan, Republic of China); Hou-Chen Hsu (National Pingtung University of Science and Technology, Taiwan, Republic of China)
For the application of visible light responsive TiO2/Fe3O4 powders in disinfection of fish pathogens is hindered by the recovery of the powder from water. The TiO2 sol-gel is evaluated to immobilize TiO2/Fe3O4 powder on glass using spin coating. TiO2/Fe3O4 powders are synthesized at various molar ratios of TiO2 to Fe3O4. The 1.5μm thickness film with rough and cracked surface is formed. It contains 30 nm diameter particles, anatase TiO2 and Fe3O4 after analysis using SEM and XRD. According to indigo carmine dye degradation assay using visible light, the optimal percentage of TiO2 sol-gel to TiO2/Fe3O4 powder is 0.4 g/ml. The efficiencies of anti-fish bacterial pathogens are 50% for E. tarda and 20% for A. hydrophila meanwhile deformed bacteria or damaged bacterial cell membranes are observed at 3 hours visible light irradiation. These results indicate the feasibility of coating TiO2/Fe3O4 on aquarium glass for reducing the fish pathogen concentration and minimizing the disease prevalence in aquarium without using UV light.
4:50 PM D2-2-11 Novel Functionalization of Anodized Ti6Al4V Nanotubes through Thermal Oxidation Approach
Sweetu Patel, Christos Takoudis (University of Illinois at Chicago, US)

Biocompatible metal implants for retaining normal functionality have been given special attention in the field of dentistry and orthopaedics. Ti-V alloy has shown to extend the life span of implants due to its high biocompatibility, high mechanical resistance, low density, high corrosion resistance, and atoxicity. Implants’ success rate also depends on osseointegration. Material properties such as wettability, roughness, surface energy and composition are key factors that affect osseointegration. In addition to micro and nano-roughening techniques such as sandblasting/acid etching and anodization, other techniques such as thermal oxidation, atomic layer deposition and chemical vapor deposition have been introduced to generate TiO2 coatings for improved surface properties. TiO2 has also been shown to improve and accelerate osseointegration through bone morphogenic protein signaling, apatite formation, and up-regulation of collagen II, osteocalcin, biglycan, collagen I, osteopontin and TGF-β1. TiO2 layers protect the bulk Ti-V from dissociating cytotoxic aluminum and vanadium ions into the biological environment. Furthermore, TiO2 is known to readily react with water to form hydroxyl groups on its surface, increasing surface energy and promoting cellular attachment. Recently, anodized TiO2 nanotubes (TNTs) have shown to enhance cellular response of human mesenchymal stem cells due to increased surface area for cellular adhesion. TNTs 50 nm in diameter was formed by electrochemically anodizing Ti-V in 0.2 wt.% ammonium fluoride (NH4F, 48% aqueous solution) in ethylene glycol with an applied voltage of 60 V DC for 3 hours. Anatase TNTs are preferred over amorphous or rutile as it resembles the crystalline structure of hydroxyapatite, which plays a key role in bone repair. Optimal parameters for forming anatase TNTs can be obtained by calcinating TNTs at 300, 450, 600 and 700 °C for two different durations, 3 and 6 hours. Annealing TiO2 at 300 °C is known to convert amorphous into anatase TiO2. Annealing at 450 °C is reported to promote anatase, while at 600 °C a majority of rutile with little anatase is formed. Finally, at 700 °C the rutile structure is anticipated to form. Advancing this project further will be discussed by performing surface characterizations including goniometry, scanning electron microscopy and other techniques that provide information regarding hydrophilicity, surface topography and surface composition of treated TNTs. Cellular growth is known to be more efficient on surfaces with higher hydrophilicity and higher anatase TiO2 content rather than on surfaces which are hydrophobic, amorphous or rutile.

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