Poster Z17 - Rapid Prototyping of Ultraflexible, Biodegradable Neural Electrodes on Polycaprolactone Substrates

Introduction: In the realm of brain-machine interfaces, polymers are considered promising substrates, offering flexibility, degradability, lightweight, durability, electrical insulation, and biocompatibility[1]. Conventional methods typically involve the use of heat and harsh chemicals, which pose a challenge when handling temperature-sensitive polymers. Addressing this challenge, inkjet printing and photonic sintering of nanoparticle-based electrodes offer solutions as they are both room-temperature processing techniques [2, 3]. Gold, silver, and copper nanoparticles are favored for their electrical properties, with gold preferred for biocompatibility. This paper centers its focus on the identification of optimal parameters for gold nanoparticle sintering. The goal is to achieve effective consolidation of nanoparticles while mitigating any potential harm to the polymer substrate.

Materials and

Methods: The fabrication process initiates with substrate preparation, involving spin-coating a 15% w/v PCL solution onto glass slides to create thin films of 10 micrometers. Inkjet printing using FUJIFILM Dimatix 2850 printer deposits an array of gold electrodes (JG-125 water-based gold nanoparticle (AuNp) ink, 25 wt%) at room temperature. The achieved electrodes had a diameter of with 150µm. Gold nanoparticle sintering, performed using the XENON X-1100 machine, was done 4 hours post-printing, utilizing precisely controlled, high-intensity light pulses. Prior to photonic sintering, oxygen plasma etching enhances conductivity and eliminates the need for a four-hour drying period. Insulation of the leads was done using UV-curable inkjet-printable resin. Electrochemical characterization was performed to assess the impact of different sintering parameters and plasma etching through impedance spectroscopy and cyclic voltammetry using a Potentiostat/Galvanostat/ZRA system. Finally, in-vivo testing of the electrodes for rat brain recording was conducted, where seizures were induced via intra-amygdala kainic acid injection.

Results, Conclusions, and Discussions: An array of gold electrodes was successfully printed on PCL. Single-pulse photonic sintering at energy densities varying from 150 to 450J revealed optimal impedance of 1.02 KΩ at 400 J, with cyclic voltammetry indicating efficient electrochemical performance. Burst mode sintering demonstrated similar electrochemical outcomes at 350 J with three pulses, achieving a conductance of 1.45 KΩ with less effect on the substrate material. The addition of plasma treatment of 4 seconds improves conductivity, reduces energy usage, minimizes substrate damage, and eliminates drying time. Electrophysiological recordings, captured effectively using the printed electrodes, revealed clear epileptic phases characterized by spike wave discharges and polyspikes.
REFERENCES
[1] Z. Hu, Q. Niu, B. S. Hsiao, X. Yao, and Y. Zhang, "Bioactive polymer-enabled conformal neural interface and its application strategies," Materials Horizons, vol. 10, no. 3, pp. 808-828, 2023.
[2] S. K. Sarkar, H. Gupta, and D. Gupta, "Flash light sintering of silver nanoink for inkjet-printed thin-film transistor on flexible substrate," IEEE Transactions on Nanotechnology, vol. 16, no. 3, pp. 375-382, 2017.
[3] C. El Hajjaji, N. Delhote, S. Verdeyme, M. Piechowiak, and O. Durand, "Optimization of the conductivity of microwave components printed by inkjet on polymeric substrates by photonic sintering," in 2020 50th European Microwave Conference (EuMC), 2021: IEEE, pp. 380-383.

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