A method of providing a biocompatible PEG-comprising coating on a substrate, without the use of an underlying adhesion layer. The coating is vapor deposited onto the substrate from a precursor which includes a PEG-derived moiety and an amino silane-containing functional group which reacts with the substrate. The substrate may be metal or plastic, where plastic excludes polyimide and polycarbonate. The substrate may be plasma treated prior to deposition of the PEG-comprising coating.