In vitro and in vivo biostability assessment of chronically-implanted Parylene C neural sensors

Abstract

Parylene C has rapidly gained attention as a exible biomaterial for a new generation of chronic neural probes. However, polymeric material failure in the form of delamination, swelling or tearing, often compromises device biostability in the long term. This work constitutes a rst step towards lifetime assessment of Parylene C implanted devices. We have conceived a Parylene C-based neural probe with PEDOT-nanostructured gold electrodes for the recording of brain activity. The material response to its biological environment was studied through in vitro soaking tests and in vivo wireless recordings in mice brain, both carried out for up to 6 months. Impedance monitoring and SEM images indicate that over the length of this trial, none of the implants presented with apparent signs of material degradation.Packaging reliability was a predominant factor in device failure, with a certain number of faulty connection appearing over time. This parameter aside, all soaked devices were stable in Articial Cerebro-Spinal Fluid, with impedances within 10% of their initial value after 6 months at 37°C. Besides, at least 70% of the implanted device were able to accurately record wirelessly high amplitude hippocampal Local Field Potentials from freely-moving mice, with steady Signal-to-Noise Ratio. In other terms, Parylene C implantable sensors responded minimally to articial and actual physiological conditions during a period of 6 months, which makes them promising candidates for reliable, chronically implanted sensors in the biomedical eld.

Stability of PEDOT:PSS‐Coated Gold Electrodes in Cell Culture Conditions

“…Successful strategies for active electrode durability include promoting polymer‐substrate adhesion with nanostructured platinum and iridium oxide . For recording, only a small number of studies to date have explored the stability of PEDOT:PSS for more than a few weeks . Generally, stable impedances or marginal increases (<10%) have been reported in vitro in buffered saline solutions (phosphate buffered saline or artificial cerebro‐spinal fluid) for PEDOT:PSS coatings that were deposited on metal electrodes using electrochemical polymerization .…”

Techniques and Considerations in the Microfabrication of Parylene C Microelectromechanical Systems

“…For high bond yield, alignment between the substrates is important and in the case of building a custom jig or adapting an existing flip chip bonder, the levelness and thermo-mechanical properties of the bond head are critical. In this way, ACF can be successfully used for electrical packaging to Parylene devices including ASIC integration ( Figure 10 ) [ 85 , 86 , 87 , 88 ]. In unpublished results, we achieved large-area packaging of Parylene electronics with pitch and width of contacts down to (100 µm pitch) using ACF (Dexerials CP13341-18AA, Dexerials, Tokyo, Japan).…”

Ultra-Long-Term Reliable Encapsulation Using an Atomic Layer Deposited HfO2/Al2O3/HfO2 Triple-Interlayer for Biomedical Implants

“…These conditions point toward the direction of polymer materials. Polydimethylsiloxane (PDMS), PI, and parylene(s) are being explored by a large amount of researchers for these purposes [7][8][9][10]. Despite the biocompatibility and good mechanical properties, one major disadvantage of these polymers for encapsulation is their low hermeticity towards moisture and water [11,12].…”