Suitability of SU-8, EpoClad and EpoCore for flexible waveguides on implantable neural probes

In neuroscience optogenetics was established as common research method. However, the devices used for opto-genetical stimulation, so called optrodes, are often made of stiff materials which lead to cell damage. We investigated the suitability of the epoxy based polymers SU-8, EpoClad and EpoCore for the fabrication of bendable thin-film waveguides. With the integration of such waveguides into neural electrodes flexible optrodes could be realized which would allow simultaneous stimulation at different sites. Three different waveguide types were fabricated with SU-8 and EpoClad as cladding and EpoCore as core materials. The optical losses were measured from 12.9 dB (SU-8 and air cladding) over 14.4 dB (SU-8 cladding) to 22.4 dB (EpoClad cladding). Aging in air at 23 °C for a time period of 80 days led to a continuous increase of the losses, which seemed to adapt to an upper limit of over 20 dB. Samples aged in saline solution at 37 °C showed a faster increase in the first 20 days, but a similar upper limit.