A Simply Fabricated Neural Probe by Laser Machining of a Thermally Laminated Gold Thin Film on Transparent Cyclic Olefin Polymer

Abstract

In this study, we propose a simple fabrication process of a neural probe based on the cyclic olefin polymer (COP). COP is a biocompatible material characterized by strong adhesion to gold and high UV transparency. Because of such adhesion, a gold thin film can be thermally laminated on a COP substrate using a heating press without an adhesion layer. In addition, the gold thin film can be micromachined by a UV laser without damaging the COP substrate, because the COP substrate has UV transparency. Compared with metal deposition and photolithography techniques used to fabricate conventional polymer-based neural probes, our process of fabricating a COP-based neural probe has no need of masks, vacuum, and fabrication facilities. A COP-based depth neural probe with a shank length of 10 mm was fabricated by the proposed process; this COP-based neural probe consists of four channels, each of which has a geometrical surface area of 100 × 100 μm (an average impedance magnitude of 14.8 ± 0.857 kΩ at 1 kHz). Based on multiple COP layers, the COP-based neural probe features adjustable elastic modulus (1.098–2.001 GPa). This elastic modulus was measured using buckling tests with varying thicknesses of 50, 100, and 200 μm. Furthermore, simultaneous multichannel neural signal recording was performed in vivo to assess the functionality of the COP-based neural probe. The results demonstrated the feasibility of the COP-based neural probe as a flexible depth neural probe with controllable stiffness.

Emerging Encapsulation Technologies for Long-Term Reliability of Microfabricated Implantable Devices

“…Optical transmittance of COC higher than 92% in the wavelength range of 300–1100 nm [148] has first encouraged various biomedical studies to explore the COC in optical applications such as optical fiber for biosensing or optrode for implantable optogenetic devices [149,150,151,152]. The first use of COC for encapsulation as well as substrate material of implantable device has demonstrated a COC-based multichannel neural probe in which a cover COC film is thermally laminated onto the substrate COC film with gold patterns at 235 °C.…”

“…The first use of COC for encapsulation as well as substrate material of implantable device has demonstrated a COC-based multichannel neural probe in which a cover COC film is thermally laminated onto the substrate COC film with gold patterns at 235 °C. [148]. Although no long-term reliability test has been reported as far as we understand, the exceptionally low moisture absorption rate of COC is certainly the most promising property of COC as an emerging packaging material that can provide both good hermeticity and optical transparency.…”

Implantable Thin Film Devices as Brain-Computer Interfaces: Recent Advances in Design and Fabrication Approaches

“…In addition to 3D printing, some other processes are also successfully applied to obtain the high-resolution electrodes instead of the mask patterning, which simplify the process to some extent. Shinyong et al developed a simple laser machining process of a neural probe based on the cyclic olefin polymer (COP) (Figure 6d) [103]. Due to the good adhesion to gold, the gold film can be thermally laminated on the COP substrate using a heating press without an adhesive layer.…”

Virtual electrodes generated by focused penta‐polar current stimulation for neuromodulation

“…An electrode material was 100 nm thick gold and a substrate material was a 50 μm‐thick cyclic olefin polymer (COP). Both materials were chosen because electrodes based on them can be simply fabricated using the process developed in our previous study [15]. Additionally, an ambient condition around the electrodes was filled with phosphate buffered saline (PBS) solution, as an electrolyte, in order to mimic in vivo environments.…”

“…2 c . The designed stimulation electrodes were fabricated using COPs (ZF14 and ZF16, Zeon Corporation, Japan) and thin gold films (Hanil Gold Leaf Co., Korea) by thermal lamination and laser machining [15]. An averaged impedance of the stimulation electrodes was measured to be 2.23 kΩ at 1 kHz by an impedance analyser (SI 1287 and SI 1260, Solartron Analytical, UK).…”