Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes

Abstract

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass.

Wireless, miniaturized, semi-implantable electrocorticography microsystem validated in vivo

“…5b, is an indication of the existance of no considerable redundancy in the www.nature.com/scientificreports/ signals being recorded. Figure 5c shows the spectrogram of all the 6 channels, in which frequency content of the recorded spontaneous activities are spread up to around 300 Hz, as reported in the literature 16,17,26,27 . Colormap diagram for the RMS amplitude of all the 6 channels is shown in Fig.…”

Sub-millisecond Control of Neuronal Firing by Organic Light-Emitting Diodes

“…We recently demonstrated the photophysical stability of light emitting polymers after extensive immersion to cell-culture medium (Matarèse, 2017). In addition, we have demonstrated the stability and biocompatibility of key OLED electrodes (ITO, gold, aluminum, and silver) when exposed to the physiological milieu (Falco et al, 2016; Matarèse et al, 2018). Nonetheless, the difficult challenge of implantable fully biocompatible OLEDs remain on the electrode injection materials used in devices that are inherently very sensitive to moisture and oxygen (Matarèse, 2017).…”

Perspectives on smart stents with sensors: From conventional permanent to novel bioabsorbable smart stent technologies

“…The polymer stent was 3D printed from biodegradable polycaprolactone, and sensor was made of a photosensitive and biocompatible SU-8 polymer (Figure 3(b,c)). SU-8 polymer is biocompatible with stable electro-optical characteristics making it an attractive material for bioelectronics (Matarèse et al, 2018); however, it is not bioabsorbable. One year later, with further refinement of material technology, the same research group has developed a fully absorbable smart stent system based on poly(D-lactide) (PDLA) wireless pressure sensor and the same 3D printed polycaprolactone stent as shown in Figure 3(d-e) (Park, Kim, Park, & Lee, 2019).…”