Assessing biocompatibility of materials for implantable microelectrodes using cytotoxicity and protein adsorption studies

Implantable microelectrodes have the potential to become useful tools for recording from and/or stimulating cells of the nervous system in paralysed individuals, or as part of neural prostheses for amputees. Once implanted into the body, these electrodes are expected to remain functional for many years; therefore the materials must be compatible within their biological environment, in order to minimise complications and implant failure. In this study, the biocompatibility of materials for electrode sites has been investigated using two measures: cytotoxicity and protein adsorption. The cytotoxic effects of materials on cells have been investigated using neutral red assay, and adsorption of proteins onto materials has been investigated using atomic force microscopy and ellipsometry. Materials investigated in this study are gold (Au), platinum (Pt), iridium (Ir), indium tin oxide (ITO) and titanium (Ti). Ti has been chosen as a reference material because it is a long established implant material. After 72 hours of exposure to fibroblast cells, Au, ITO, and Ir show no inhibitory effects on cell growth, whereas Pt and Ti show greater amounts of growth inhibition. The protein adsorption to different materials shows a steady growth following the initial adsorption pattern. After 24 hours of exposure to plasma, Ti had the thickest and ITO had the thinnest layer of adsorbed protein.