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978-3-8439-3617-0, Reihe Mikrosystemtechnik
Development of Flexible Optrodes with Potential Long-term Applicability
206 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2018), Softcover, B5
For the realization of reliable, transcutaneously leading optrodes, which are suited for chronic applications in brain research, flexible optical waveguides were developed such that they could be integrated into approved polymer-based electrode arrays.
The choice of waveguide materials was conducted under consideration of technical as well as biomedical requirements. Upon long-term investigation of optical properties, two medical grade silicone rubbers were defined as the materials of choice, namely the polydimethylsiloxane elastomers (PDMS) MED-1000 as cladding and MED-6755 as core material.
The waveguide's fabrication process was based on laser-patterning. This well-established rapid prototyping method provided high design flexibility and facilitated both optical interconnection via ferrule coupling and integrability into PDMS-based electrode arrays.
Careful characterization of the waveguides was performed, including consideration of stretching and bending. It revealed good coupling efficiency with coupling losses of -0.8 to -1.1 dB. As a consequence of the laser-patterning process, however, propagation loss of straightly aligned waveguides was comparatively high (-14.4 +/-3.6 dB/cm).
A ceramic adapter was developed for the assembly of electrode arrays made of polyimide (PI). It allowed miniaturization of the implant's head-mounted part and offered a robust electrical interconnection which survived more than 400 mating cycles in a long-term in vivo study. Thus, the basis for the optrodes' assembly was set.
Flexible optrodes were successfully fabricated in which the waveguides were merged with PI-based shaft electrodes. In doing so, an intermediate adhesion promoting layer, a compound of amorphous silicon carbide and silicon oxide thin-films, was applied which had been investigated in an accelerated aging study. Finally, implementation of the ceramic adapter concept yielded reliable electrical and optical interconnection of the optrodes.