title: Long-term evaluation of a liquid crystal polymer (LCP)-based retinal prosthesis.
abstract: OBJECTIVE
  The aim of this study is to evaluate the long-term reliability of a recently presented liquid crystal polymer (LCP) -based retinal prosthesis in vitro as well as in vivo. Because an all-polymer implant introduces another intrinsic leak type due to gas permeation, for which the traditional helium leak test for metallic packages was not designed to quantify, a new method to investigate its durability is required.
  
  
  METHODS
  We designed and carried out a series of reliability tests specifically for all-polymer implants by quantitatively investigating moisture ingress through various pathways of the polymer surface, and the polymer-polymer and polymer-metal adhesions. Moisture permeation through the bulk material was estimated by analytic calculation, while water ingress through the adhesively sealed LCP-LCP and LCP-metal interfaces was investigated using the separate parts of an electrode array and a package in an accelerated aging condition. In vivo tests were done in rabbits to examine the long-term biocompatibility and implantation stability by fundus observation and optical coherence tomography (OCT) imaging.
  
  
  RESULTS
  The analytic calculation estimated good barrier properties of the LCP. Samples of the LCP-based electrode array failed after 114 days in 87 °C saline as a result of water penetration through the LCP-metal interface. An eye-conformable LCP package survived for 87 days in an accelerated condition at 87 °C. The in vivo results confirmed that no adverse effects were observed around the retina 2.5 years after the implantation of the device.
  
  
  CONCLUSIONS
  These long-term evaluation results show the potential for the chronic use of LCP-based biomedical implants to provide an alternative to traditional metallic packages.
authors.affiliation: Department of Electrical & Computer Engineering, Seoul National University, Seoul 151-742, Korea.
authors.forename: Joonsoo
authors.initials: J
authors.lastname: Jeong
authors.forename: So
authors.initials: S
authors.lastname: Hyun Bae
authors.forename: Jong-Mo
authors.initials: JM
authors.lastname: Seo
authors.forename: Hum
authors.initials: H
authors.lastname: Chung
authors.forename: Sung
authors.initials: S
authors.lastname: June Kim
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000008:administration & dosage / Q000592:standards; D004567:Electrodes, Implanted / Q000592:standards / Q000639:trends; D004867:Equipment Design / Q000592:standards* / Q000639:trends; D011108:Polymers / Q000008:administration & dosage / Q000592:standards*; D011817:Rabbits; D012160:Retina / Q000502:physiology* / Q000601:surgery; D013997:Time Factors; D057488:Visual Prosthesis / Q000592:standards* / Q000639:trends
chemical_list: D001672:Biocompatible Materials; D011108:Polymers; C422409:liquid crystal polymer