The role of flexible polymer interconnects in chronic tissue response induced by intracortical microelectrodes--a modeling and an in vivo study.

Chronic tissue response induced by tethering is one of the major causes for implant failure in intracortical microelectrodes. In this study, we had explored the hypothesis that flexible interconnects could provide strain relief against forces of "micromotion" and hence could result in maintaining a healthy tissue surrounding the implant. Finite element modeling results indicated that flexible interconnects, namely polyimide (E=2 GPa) and polydimethylsiloxane (PDMS, E=6 MPa), reduced the interfacial strain by 66% and two orders of magnitude, respectively. Quantitative immunohistochemistry results indicated that significant neuronal loss occurred up to 60 mum from the implant interface. This was strongly correlated to both glial fibrillary acidic protein (GFAP) expression and simulated strain as a function of distance away from the implant.