In vitro biological assessment of electrode materials for neural interfaces

The development of the next generation electrode interfaces for neural prosthetic devices requires high-through-put multifaceted testing strategies to assess material interactions with both peripheral and central nervous system (CNS) immune cells. The utility of a primary astrocyte enriched glial cell culture was assessed as a potential in vitro tool for understanding the immune response to electrode materials. Conductive polymer consisting of electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) doped with paratoluene sulfonate (pTS) was used as a novel electrode material and compared to the conventional electrode material, platinum (Pt). Morphology of astrocytes and microglia in contact with the materials was analyzed and compared to an immunoassay of TNFα release from human blood plasma. While all electrode materials failed to stimulate TNFα release from human leukocytes, the materials in contact with glial cells resulted in progressive reactive gliosis. This primary astrocyte in vitro assay provides insight into the degeneration of electrode performance in vivo as a result of scar tissue reactions in chronic implant devices. It also highlights the relevance of testing for immune reactions with an appropriate cell system.