Pit initiation on biomedical alloys-A review.

Biomedical alloys, like many engineering alloys, have chemical or physical heterogeneities at the surface, and such heterogeneities can potentially act as sites for pit initiation. Alloys of particular interest are 316/316L (and 316LVM) stainless steel, nitinol, and CoCr alloys. This review focuses on the sites-generally inclusions-that have been associated with pitting in various studies of biomedical alloys in simulated physiological solutions.

The effect of serum proteins on the electrochemical behavior of CoNiCrMo.

Numerous studies have examined the effect of serum and blood proteins on the general corrosion of metallic biomedical materials. However, it is unclear whether proteins have any effect in the case of CoCr alloys, particularly at physiological concentrations. In this work, potentiodynamic polarization and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of Co-35Ni-20Cr-10Mo in PBS, PBS with albumin at a concentration (36 g/L) representative of serum, and bovine serum.

The passive behavior of biomedical alloys in simulated physiological solutions.

Passive alloys are commonly considered to exhibit a current that is essentially independent of potential over the passive range in neutral chloride solutions. However, the current-potential dependence of Ti and its alloys, CoCr alloys, and 316L stainless steel in buffered, simulated physiological solutions containing phosphate differs from that usually reported for the alloys in chloride-only solutions. An analysis of potentiodynamic polarization data from previous studies showed that these alloys typically exhibit an exponential dependence of current on potential-as reflected by Tafel-type behavior-over the initial part of the passive range in buffered solutions.

Comparison of the electrochemical behavior of CoCrWNi, CoCrFeNiMo, and CoNiCrMo alloys.

Numerous studies have examined the electrochemical behavior of Co-28Cr-6Mo and Co-35Ni-20Cr-10Mo in simulated physiological solutions. However, two other CoCr alloys-Co-20Cr-15W-10Ni and Co-20Cr-16Fe-15Ni-7Mo-have received relatively little attention. In this work, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of as-received and passivated CoCrWNi and CoCrFeNiMo in phosphate-buffered saline.

The use of electrochemical techniques to evaluate the corrosion performance of metallic biomedical materials and devices.

The corrosion performance of metallic biomedical materials and devices is commonly evaluated using electrochemical techniques. Although test standards involving such techniques have been released to address some forms of corrosion, a key issue is application of the results with regard to use of an implantable device in vivo. This review focuses on nitinol, 316L/LVM stainless steel, and Co-Cr alloys and is intended to provide some perspective on the significance of results from tests concerning general corrosion, localized corrosion, galvanic corrosion, and fretting corrosion of these alloys in simulated physiological solutions.

Pit initiation on nitinol in simulated physiological solutions.

Inclusions appear to play a crucial role in the initiation of pitting on nitinol, but the reason remains unclear. Furthermore, it has not been established whether the type of inclusion is a central factor. In this study, potentiodynamic polarization together with scanning electron microscopy and energy dispersive X-ray spectroscopy were used to provide more insight into the initiation of pits on electropolished nitinol wire.

The electrochemical behavior of nitinol in simulated gastric fluid.

Increased use is being made of nitinol for implants that are exposed to gastric fluid. However, few corrosion studies have involved nitinol in an appropriate acidified chloride solution. In this work, the electrochemical behavior of electropolished (EP) nitinol was examined in simulated gastric fluid, the corresponding neutral solution with the same concentration (0.

Galvanic corrosion of nitinol under deaerated and aerated conditions.

Various studies have examined the corrosion rate of nitinol generally under deaerated conditions. Likewise, galvanic corrosion studies have typically involved deaerated solutions. This work addressed the effect of galvanic coupling on the corrosion current of electropolished nitinol in phosphate buffered saline and 0.

Corrosion behavior of nitinol in blood serum and PBS containing amino acids.

The susceptibility to localized corrosion of metallic, implant medical devices is typically evaluated in a simulated physiological solution, such as phosphate buffered saline (PBS). For implant devices in contact with blood, the underlying premise is that proteins and other components in blood do not significantly change the corrosion susceptibility. This study examined the corrosion behavior of nitinol in bovine serum and PBS containing amino acids (cysteine, glutamine, and tryptophan).

Electrochemical behavior of cobalt-chromium alloys in a simulated physiological solution.

Several cobalt-chromium alloys such as MP35N are used for biomedical implants. The electrochemical behavior of these alloys in the passive range differs from that of other biomedical alloys. In particular, their cyclic potentiodynamic polarization curves exhibit an increase in current at a potential of about 0.

The electrochemical behavior of nitinol in simulated physiological solutions.

The electrochemical behavior of nitinol in simulated human bile and phosphate-buffered saline (PBS) was examined using electrochemical impedance spectroscopy. In addition, cyclic potentiodynamic polarization tests were performed in the simulated bile and salt-only bile, and the results compared with those obtained previously in PBS. The potentiodynamic tests showed that electropolishing was effective in providing nitinol with a high resistance to pitting corrosion in the bile solutions, as found in PBS.

Susceptibility of nitinol to localized corrosion.

The effect of different conditions on the susceptibility of nitinol to localized corrosion was examined using the cyclic potentiodynamic polarization technique. Tests were performed on mechanically polished (MP) and electropolished (EP) nitinol wire in 0.9 wt % NaCl and phosphate-buffered saline (PBS).