Nonspecific adsorption of proteins is a challenging problem for the development of biocompatible materials, as well as for antifouling and fouling-release coatings, for instance for the marine industry. The concept of preparing amphiphilic systems based on low surface energy hydrophobic materials via their hydrophilic modification is being widely pursued. This work describes a novel two-step route for the preparation of interpenetrating polymer networks of otherwise incompatible poly( dimethylsiloxane) and zwitterionic polymers. Changes in surface hydrophilicity as well as surface charge at different pH values are investigated. Characterization using atomic force microscopy provides thorough insight into surface changes upon hydrophilic modification. Protein fouling of the materials is assessed using fibrinogen as a model protein.