ICMCTF 2012! - CD-Lab Application Oriented Coating Development

2:50pm D3-1-5 An Electrochemical Investigation of TMJ Implant
Metal Alloys in a Synovial Fluid-Like Environment: The influence of
pH variation, D. Royhman (droyhman@gmail.com), University of Illinois
at Chicago, College of Dentistry, US, R. Radhakrishnan, M.T. Mathew, M.
Wimmer, Rush University Medical Center, US, C. Sukotjo, University of
Illinois at Chicago, College of Dentistry, US
Temporomandibular Joint (TMJ) disorder affects 30 million Americans,
with approximately 1 million new patients diagnosed each year. These
pathologic conditions may require reconstruction with total joint prosthesis
(TMJ implant) for better treatment prognosis. A total TMJ implant is a
metal-on-metal joint, usually made of titanium, cobalt-chromium, or
combination of both. In the body environment, the TMJ implant is exposed
to variable corrosive conditions from the electrolytic environment, as well
as the galvanic effect between the different metals. The primary reason for
implant rejection is breakdown and corrosion. Corrosion can severely limit
the strength and lifespan of the implant, leading to implant fracture and
adverse physiological effects. The objective of this study was to examine
the effect of different levels of pH of BCS under simulated physiological
conditions on the corrosion behavior of commonly used TMJ implant
metals. Corrosion behavior was evaluated using standard electrochemical
corrosion techniques and galvanic corrosion techniques. Standard
electrochemical corrosion tests were run using a 3-electrode cell as a
function of metal type (CoCrMo and Ti6Al4V) and pH (3.0, 4.5, 6.0, and
7.6). Evaluation parameters included: Open Circuit Potential, EIS
parameters (Rp and Cp), and Cyclic Polarization parameters (Ecorr, Icorr,
and Ipass). Galvanic corrosion tests were run using a 3-electrode cell with
Ti6Al4V as the working electrode, CoCrMo as a counter electrode, and a
saturated calomel electrode (SCE) as the reference electrode (n=3). Data
was evaluated using Two-way ANOVA, Tuckey’s post hoc analysis, and
two-sample independent t-test (p=0.05). The metal surfaces were
characterized using white-light-interferometry microscopy and scanning
electron microscopy (SEM). The cyclic polarization scan showed that
Ti6AL4V had an enhanced, stable, passive layer growth and a better
corrosion resistance than CoCrMo. EIS measurements indicated that Rp
was inversely related to increased pH. Initial galvanic corrosion
measurements exhibit the noble electrochemical behavior of Ti6Al4V. SEM
and white-light-interferometry images demonstrate a higher increase in
surface roughness (Ra) after corrosion in CoCrMo. We concluded that
acidity in BCS accelerated the ion exchange between the Metal-electrolyte
interface in both metal types and that Ti6Al4V shows better corrosion
behavior than CoCrMo. Additionally, corrosion kinetics are influenced by
the potential corrosion inhibition properties of the protein content of the
surrounding fluid. Further studies are in progress to generate a better
understanding of the transitions in the corrosion kinetics due to these
proteins.
3:10pm D3-1-7 Fretting corrosion with proteins: the role of organic
coating about the synergistic mechanisms, J. Geringer
(geringer@emse.fr), J. Pellier, B. Forest, ENSM-SE, France, D.
Macdonald, CEST-PSU, US INVITED
Fretting corrosion is one of the most deleterious mechanisms for the
degradation of metallic biomaterials, especially in the orthopedic field.
Around 1.5 million of hip prostheses are implanted worldwide. This work is
dedicated to study the synergistic effect of proteins and ions concentration
on the wear of stainless steel, 316L, against a polymer sample under
fretting-corrosion conditions.
A specific device allows reproducing fretting corrosion, i.e. relative
displacements of microns between materials in contact. In order to compare
with previous investigations, the amplitude was equal to ± 40 µm with
sinusoid dal amplitude. The duration of each test was 14400 s, 4 hours.
The 316L sample size was the same for all samples. 3D roughness of 316L,
Ra (3D), was 10 ± 2 nm. PMMA (PolyMethyl Methacrylate) is cylindrical
with a roughness of 35 ± 5 nm. 4 solutions of NaCl were selected in order to
study the effect of the ionic strength: 10 -3 mol.L -1 , 10 -2 mol.L -1 , 10 -1 mol.L -1
and 1 mol.L -1 . Additionally on each solution described previously,
concentrations of proteins (pure albumin) were: 0, 1 and 20 g.L -1 .
Experiments were investigated at temperature of 22 ± 1 °C. The potential
was equal to -400 mV/SCE and the current density was measured with a
particular attention to the device insulation.
The synergistic formalism is:
W = Wc +Wm + (DWcm + DWmc); W: total wear volume; Wc: wear volume
due to corrosion; Wm: wear volume due to mechanics; DWcm: synergistic
wear volume, corrosion enhances wear due to mechanic; DWmc:
synergistic wear volume, mechanic enhances wear due to corrosion.
As expected, the main wear volume of stainless steel is due the synergistic
terms for a salts concentration close to the one of human physiological
liquid. 10 -1 mol.L -1 is the threshold concentration for increasing wear and
the part of the synergy effect. At 10 -3 mol.L -1 of NaCl, the content of
albumin has no significant impact on the wear volume. For fixed salts
Monday Afternoon, April 23, 2012 16
concentration higher than the threshold, albumin does not promote the wear
of stainless steel surface, it decreases (divided by 3 from 0 g.L -1 to 20 g.L -1 ).
The mechanical wear, calculated at applied potential of -800 mV/SCE, does
not change according to the albumin concentration.
The most interesting point is the albumin changes the mode of synergy. At
0 g.L -1 of albumin, the main synergistic term is the influence of mechanics
on corrosion, DWmc. On the contrary, at 20 g.L -1 , the main synergistic term
is the influence of corrosion on mechanics, DWcm. One might suggest
albumin promotes the corrosion after mechanical damage of the passive
film. However albumin prevents from mechanical degradation.
3:50pm D3-1-9 Optimisation of Pulsed Bipolar Plasma Electrolytic
Oxidation of Magnesium Alloy for Biological Applications, Y. Gao, A.
Yerokhin (A.Yerokhin@sheffield.ac.uk), A. Matthews, University of
Sheffield, UK
Magnesium alloys have been considered as promising biomaterials,
although their application in biological area is limited by poor corrosion
resistance. Plasma electrolytic oxidation (PEO) has been investigated to
solve this problem. Alternating current regimes, for example a pulsed
bipolar current (PBC) mode, offer a better control over the PEO process and
correspondingly the coatings exhibit higher corrosion resistance compared
with those produced in DC mode. Intrinsic problems of the PEO process are
associated with low energy efficiency, since significant fraction of current is
consumed on collateral electrode processes, such as gas evolution and
anodic dissolution of metal substrate. Evaluation of the collateral processes
is essential to both understand the coating formation mechanism and
optimise the coating process in terms of energy efficiency. In the present
study, current efficiency of PBC PEO process is investigated and the
corrosion performance of the coatings is also studied. For this purpose, PBC
current mode with variable frquency and duty cycle is employed to treat a
magnesium alloy in an alkaline electrolyte solution. Gas evolution rate and
its composition are determined, together with the amount of substrate
material lost to the electrolyte. An online gas flow meter and a residual gas
analyser (RGA) equipped with a quadrupole mass spectrometer are utilised.
This set-up provides a safe and reliable way to evaluate partial electrode
processes during PBC PEO treatment. The corrosion performance of the
PEO coated magnesium alloy is tested in a simulated body fluid (SBF) at 37
o C using an electrochemical workstation. Based on the experimental results,
current efficiency and bio-corrosion performance of PEO coatings are
optimised.
4:10pm D3-1-10 Micro-textured CoCrMo Alloy for MoM joints: An
Electrochemical Investigation, C. Nagelli
(christopher_nagelli@rush.edu), M.T. Mathew, Rush University Medical
Center, US, RP. Pourzal, F. Liedtke, A. Fischer, University of Duisburg-
Essen, Germany, M. Wimmer, Rush University Medical Center, US
In orthopedics, the use of metal-based alloys is a reoccurring practice
because of their biocompatibility, low-wear rates and post-operative
stability. However, metal-on-metal (MoM) hip joint bearings endure a
constant load during articulation while immersed in synovial fluid. This
environment has shown to be detrimental because of leaching metal ions
and particulate debris in the neighboring tissue that has lead to implant
failure and revision surgery. Currently, MoM joints are facing serious
challenges with market usage declining from 35% to less than 10%.
Tribochemical reactions potentially generate a type of tribolayer on the
surface, which has shown a better electrochemical and tribological
behavior. However, this layer is very unstable, nonhomogeneous and patchy
in appearance. A defined micro-topography of the surface could be a
solution facilitating strong film growth. To address these concerns, the aim
of the current work is to investigate electrochemical properties of 5 types of
topographies on a CoCrMo alloy surface.
Five different topographies were prepared using electrochemical etching.
The topographies were adjusted by applying a different current during the
etching process. The textured samples were than compared to a control
sample that was polished using a conventional polishing process. Corrosion
tests were conducted in an electrochemical cell with bovine calf serum (30
g/L protein) as the electrolyte. A standard corrosion test protocol was used
that included monitoring of the open circuit potential for 1 hr and an
electrochemical impedance spectroscopy test with a frequency range of
100K Hz to 0.005 Hz. Samples were then polarized during the cyclic
polarization test from -0.8 V to -0.8 V with a peak voltage of 1.8 V. The
surfaces were then characterized using a white light interferometer and
scanning electron microscope.
The surfaces with a micro-topography demonstrated an improved corrosion
behavior when compared to the control sample. Texturing the surface
results in an even distribution of surface depressions. It appears that this
topography enhances the adherence of protein resulting in a decelerated
corrosion rate. Thus, a micro-topography of the surface is ideal for creating
a heterogeneous proteinaceous layer that is analogous to a tribolayer, which