<i>In vitro</i> and <i>in vivo</i> evaluation of ultrananocrystalline diamond for coating of implantable retinal microchips

Abstract

In this work, ultrananocrystalline diamond (UNCD) thin films were evaluated for use as hermetic and bioinert coatings for a retinal microchip. These films were deposited on highly conductive Si substrates at different temperatures (from 400 to 800 degrees C), using microwave plasma enhanced chemical vapor deposition with argon-rich Ar/CH4 gas mixtures and different relative amounts of hydrogen (0-20%). Scanning electron microscopy studies showed that all the films are dense and continuous. Results of cyclic voltammetry test revealed that when there was <2% of hydrogen in the plasma, the film obtained renders the surface electrochemically inactive, with very low leakage currents ( approximately 4 x 10(-7) A/cm2 at +/-5 V). In addition, in vivo tests of the UNCD-coated Si samples were performed by implanting them in the eyes of rabbits for 4-6 months within the eye physiological environment. According to all these results, it was concluded that UNCD is a promising candidate for use as the encapsulating coatings for implantable retinal microelectronic devices.