In vitro and in vivo evaluation of ultrananocrystalline diamond for coating of implantable retinal microchips

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°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