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W.J. Foster, E.B. Trexler, A. Zomorrodian, S. Stahl, N. Wu, S. Uwaydat, C.A. Garcia, A. Ignatiev; Development of Ceramic Optical Microdetectors for Retinal Implantation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1519.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The goal of this research is to develop a photoreceptor prosthesis based upon a photo–ferroelectric thin film epitaxially grown on a Pt thin film using pulse laser deposition. This system utilizes localized electric field polarization for stimulation rather than relying upon injection of current, with its inherent heating and related effects. Methods: La–doped PbZrTiO3 (PLZT) was epitaxially grown on a Pt thin film and patterned using photolithography and ion milling. This process resulted in microdetectors 80 µm in diameter and 1.5 µm in thickness in an ordered hexagonal pattern. The Pt thin film was left intact under the detectors as well as in small bridges between individual detectors. The detector array was then embedded in poly (DL–lactic–co–glycolic acid) (PLGA) to provide mechanical rigidity for surgical manipulation. In vivo tests for biocompatibility and in vitro tests for spectral sensitivity and ability to affect the potential of neighboring cells have been performed. Results: The spectral response of the detectors was found to overlap that of the human eye with a peak response at ∼550 nm and sensitivity extending out to nearly 700 nm. A 250 µm diameter devise can generate a voltage of 30 mV when illuminated at 1mW/cm2. When the intensity of the light is increased to 2000 mW/cm2, the voltage output reaches 3.5 V. The signal decays with a time constant of ∼1 second. During in vivo biocompatibility studies, changes to the retina were found to be minimal, with a well–preserved inner retina overlying the detector after implantation for up to 6 weeks. During in vitro studies, polarization of adjacent neuron–like cells (PC–12 cells) was measured utilizing standard patch–clamp techniques with and without illumination. The cells were noted to vary in their intra–cellular potential with illumination. Conclusions: Photoferroelectrics are promising materials to consider in developing a retinal prosthesis. Given the magnitude of the electric field generated, the biocompatibility, and the ability to fabricate small structures, this technology should be explored further. Further work will explore the possibility of color vision (by selecting compounds with different absorption spectra), organic monolayer coating of the detectors to improve adhesion between cells and detectors, and intra–cranial applications (where the devices can be accessed using infra–red).
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