93. nanoporous au improves metal-pedot:pss adhesion in neural electrodes

Department: Electrical & Computer Engineering
Faculty Advisor(s): Shadi A. Dayeh

Primary Student
Name: Mehran Ganji
Email: mganji@ucsd.edu
Phone: 949-537-9178
Grad Year: 2019

Abstract
In the past decade, conducting polymers have gained substantial attention to be used as the direct interfacing material between Biomedical devices and neural tissue due to their superior electrochemical properties compared to conventional metals such as Au, Pt and Ir. Particularity, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has emerged as outstanding material for neural interfaces and biomedical applications by providing lower electrochemical impedance and higher charge injection capacity. Despite their superior qualities, exploiting the full capability of such CP coatings in chronic biomedical applications have been limited due to the weak adhesion and mechanical stability of polymer coating on metal substrates. As a result, cracks or delamination from the metal film are often observed during in-vitro aging experiments, chronic implants, prolonged charge injection and mechanical stress. Here, we report that integration of Au-nanoporous (Au-np) structure on top of conventional Au electrode improves the adhesion of spin-cast PEDOT:PSS film by providing larger interface area and serving as a mechanical anchor for the PEDOT:PSS layers. We found that Au-np structure prevents the volumetric contraction/ expansion of PEDOT film; the main contributor to mechanical failure, under long-term charge injection (cyclic voltammetry). The PEDOT:PSS/Au-np interface remains stable over 1200 stressing redox cycles whereas conventional PEDOT:PSS/Au electrodes delaminated after 300-400 cycles (3-4 fold adhesion improvement). In addition, we observed that macro PEDOT:PSS/Au-np electrodes offer more stable condition compared to microelectrodes by passing 4000 redox cycles without significant morphological change nor electro-activity loss. Electroplated PEDOT:PSS film exhibited different degradation process under cycling test whereas PEDOT film tends to leach out (get thinner) gradually from metal film rather full delamination from the substrate as observed in spin-coated PEDOT electrodes. Accelerated aging tests (passive test) were performed to expose the electrodes to the wetting environment over a long time (over one month) as performed in vivo. We used a temperature of 37 C (body temperature) and 60 C (the recommended temperature for accelerated aging with polymers) and observed longer survival of the coating; the results are being validated in vivo. Overall, we believe that the reported fabrication strategy that is compatible with scalable fabrication processes can advance CP neural probes for use in chronic applications where their long-term stability is critical.

Industry Application Area(s)
Life Sciences/Medical Devices & Instruments

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