A downfall for wet chemistry, liquid coatings such as silicones, acrylics, epoxy, or urethanes is that they do not meet bio-compatibility requirements and cannot be applied with precise control. On the contrary, parylene does not out-gas and is very effective against the passage of contaminants from both the body to substrate or substrate to body.
Parylene can be applied a couple of mils thick to a few hundred angstroms in thickness, it is pin hole free, applied at room temperature, contains no additives, insoluble in most solvents, very lubricious, has a very high dielectric strength, and is biocompatible and bio-stable.
Parylene C is currently being used is a number of well documented bio-medical implantable devices. Parylene C has been proven to be a terrific biocompatible material. It is USP Class VI implantable plastic material and conforms to material ISO-10993 Biological Evaluations for Medical Applications. Parylene C is also probably the longest proven protective biocompatible material.
Parylene Technology for Neural Probes Applications. Changlin Pang. California Institute of Technology. 2008.
S. Nancy, "Literature Review: Biological Safety of Parylene C," Medical Plastics
and Biomaterials, vol. 3, pp. 30-35, March 1996.
B. Humphrey, "Using Parylene for Medical Substrate Coating," Medical Plastics
and Biomaterials, Janurary 1996.