Plasma processing represents an environmentally friendly, cost efficient and versatile method to modify materials surfaces at low temperatures. Plasma etching processes on polymers, for example, are well studied to enhance the adhesion of coatings and composite materials involving surface nanostructuring. Plasma sputtering is examined to deposit defective metal oxide coatings such as TiO_2-x containing oxygen vacancies that are doped by another metal such as Ag. Plasma post-oxidation is applied to tune the nanostructuring of the dopant forming oxidized Ag islets strongly enhancing the catalytic properties to produce reactive oxygen species (ROS). Such coatings can even be functionalized by a plasma polymer cover layer. Non-toxic antimicrobial properties are thus enabled. Plasma polymer deposition with intermittent plasma etching is explored to produce highly nanoporous thin films. Preferential etching of residual hydrocarbons in SiOx layers induces interconnected nanopores in the growing film. Such films allow water diffusion and loading with hydrogels, e.g., as lubricants. Deposition of a nm-thick hydrophobic cover layer finally enables the control of water penetration yielding the nanoconfinement of water molecules that can form a dipolar field. The adsorption of bacteria was found to be affected by the resulting water structuring. Potential biomedical and other technical applications are discussed.