Author(s): Sophia Wartena
Mentor(s): Quentin Allen
Institution BYU
Corrosion is the electrochemical deterioration of metal. Corrosion of biomedical implants can release toxins into the human body; therefore, it is important to test the corrosion resistance of metallic biomaterials. Observing metals corrode in a saline bath is prohibitively time-intensive. Accelerated testing data based on electrochemical methods are frequently collected to assess corrosion rates and biocompatibility in biomedical implants. However, it is difficult to achieve repeatable results due to the many experimental details that may introduce variability to the experiments. Accelerated corrosion testing involves connecting electrodes to a potentiostat and suspending the electrodes in a test fluid such as bovine calf serum. Samples of the biomaterial of interest (e.g., stainless steel or cobalt-chromium) act as the working electrode, with a rhodium mesh counter electrode and a silver/silver chloride reference electrode. A flat surface of the working electrode is polished and exposed to the test fluid, and other surfaces are electrically insulated to control the exposed surface area. Testing involves observing an Open Circuit Potential (OCP), and conducting Linear Sweep Voltammetry (LSV), also known as potentiodynamic polarization, to calculate corrosion rates and corrosion current densities. Preliminary experiments revealed many details that can impair or alter these complex tests, including shifting of the insulation material, surface irregularities from cutting and polishing the testing surface, improper electrical contact with the working electrode, and contact between the potentiostat connectors and the bovine serum. To resolve these issues and improve repeatability, this study altered three main categories: working electrode surface area/shape, insulation type, and electrode attachment. Of the three working electrode shapes tested (circle, square and rectangle), the rectangular samples are ideal because they reduce waste of the raw material and are easier than the original circular design to calculate precise surface area when preparing the samples. Non-conductive paint proved to be more effective than electrical tape and less time consuming than resin as an insulator between the bovine serum and the non-test surface. For electrode attachment, the copper (Cu) top mount with conductive epoxy was more secure than both the direct sample-electrode contact and Cu side mount. This method allows the test surface to be tilted as necessary without contacting the potentiostat connectors with the bovine serum and provides more flexibility with the necessary volume of bovine serum. These results provide a standard experimental method to prepare samples of biomedical materials in a manner that provides precise and repeatable corrosion data.