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Jong-Mo Seo, Changhoon Baek, So Hyun Bae, Hum Chung; Investigation of Cyclic Olefin Copolymer as Packaging Material Candidate for Electrical Retinal Stimulator. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4977.
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Implantable neural electrode is an essential component of neural prosthesis and act as interface between the prosthesis system and the nervous system. For safe, long-term implant, the electrode must be fabricated with an appropriate material; it must be biocompatible, have high chemical resistance and low water absorption rate, and appropriate tensile modulus for minimizing damage to nearby organs. Finally, it must be compatible with fabrication processes. We investigated cyclic olefin copolymer (COC) as packaging material for retinal electrode through literature review and experiment.
Literatures were reviewed for comparing characteristics of COC and other commonly used materials such as polydimethylsiloxane (PDMS), parylene-C, polyimide, and liquid crystal polymer (LCP). Furthermore, in order to prove that COC is compatible with fabrication process, a simple planar 4 x 6 electrode was fabricated. COC pellets were flattened using heated hydraulic press for substrate layer and insulating layer. The substrate layer was processed with O2 plasma surface treatment to act as better metal adhesion. Gold was deposited using E-gun evaporator and patterned using standard photolithography technique. The insulating layer was patterned for contact sites and connection pads using laser abrasion. The two layers were aligned and heat-pressed for attachment.
COC showed great biocompatibility as well as excellent chemical resistance, appropriate tensile modulus (approx. 3000 MPa) and low water absorption (0.01%). COC had lower water absorption rate than all of the other polymers compared in this investigation. PDMS had lower tensile modulus which gives it the advantage of causing less damage to nearby tissue once properly placed, but COC had much better adhesion to metal which makes it more reliable for fabrication. Also, it can be argued that the tensile modulus of PDMS is too low for handling during the implant procedure. We were able to fabricate a simple planar electrode using combination of conventional semiconductor fabrication technique and standard polymer processing technique.
We believe that COC is a strong contender for a packaging material for retinal prosthesis system, in terms of both characteristics and processability. Further investigation is under way to confirm the safety of the electrode after the proposed fabrication process.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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