A design of an implantable electronic device always takes into consideration the coating, as it is the only barrier that protects the gadget from fluids and from the natural immune responses of the body. Designing a protective coating for miniature electronics is an extremely difficult endevour. The silicon chip retinal implant is being developed by Second Sight, a company based in Sylmar, California, along with a consortium of university researchers. The device needs a hermetic case to prevent it from reacting with fluids in the eye. Researchers have developed an ultrananocrystalline diamond (UNCD) film that is guaranteed to be safe, long-lasting, electrically insulating and extremely tough. The coating can also be applied at low temperatures that do not melt the chip's microscopic circuits. The UNCD film is the first coating to meet all the necessary criteria for the implant, says Xingcheng Xiao, a materials scientist at Argonne National Laboratory, Illinois, who developed the film. The tiny diamond grains that make up the film are about 5 millionths of a millimetre across. They grow from a mixture of methane, argon and hydrogen passing over the surface of the five-millimetre-square chip at about 400 C. Xiao and his colleagues have already tested the implants in rabbits' eyes, and saw no adverse reaction after six months.