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Joonsoo Jeong, So Hyun Bae, Kyou Sik Min, Jeong Hoan Park, Jong-Mo Seo, Hum Chung, Sung June Kim; Long-term evaluations of a Liquid Crystal Polymer (LCP)-based Retinal Prosthesis in vitro and in vivo. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):752.
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© ARVO (1962-2015); The Authors (2016-present)
A miniaturized, light-weight and eye-conformable retinal prosthesis was developed using monolithic fabrication of liquid crystal polymer (LCP), and its in vitro and in vivo functionality were verified (J.Jeong; TBME 2015, ARVO 2014). The 16-channel, all-LCP device has an eye-conformable package of 14 mm in diameter and 1.3 mm in the maximum thickness with 0.38g of total weight. In this study, we present long-term testing results of the new LCP-based retinal implant to evaluate its long-term reliability and safety in vitro and in vivo.
The long-term reliability tests were conducted using the electrode part of the implant to assess the durability of LCP-metal interface which is the weakest point against water ingression compared to other leakage pathways. LCP-based retinal electrodes were soaked in PBS solution at elevated temperature of 87℃. Voltage transient was monitored under continuous stimulation (50 μA, 500μs, 30Hz) to detect water leakage. Chemical stability of Iridium oxide was examined through voltage waveforms, impedance and CSC measurements after long-term pulsing in saline at the room temperature. The long-term in vivo safety was evaluated using OCT imaging, visual and fundus observation after implantation of dummy devices into rabbit eyes for 2 years.
In the accelerated aging test, the LCP-based retinal electrodes have reached 80 days in 87℃ saline as of this writing with no significant changes in voltage waveforms under 24-hour stimulation. The impedance spectrum and CSC values of IrOx have remained unchanged from their initial values (1.7 kΩ at 1 kHz, 45.5mC/cm2) for 30 days of 30 Hz pulsing in saline. In the in vivo examination after 2-years of implantation, the system package has been well placed under the conjunctiva without causing inflammation and protrusion. The electrode array in the supra-choroidal space did not migrate and retinal structure was well preserved as confirmed by fundus observation and OCT, respectively.
In the in vitro and in vivo long-term testing, the newly developed LCP-based retinal implant showed promising results with electrodes lasting 80+ days in 87℃ and implantation stability proven for 2 years. The long-term tests using fully functional device in vitro as well as in vivo are ongoing at this moment.
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