4. PDMS has a high free volume, resulting in the unique atomic spacing of silicone, so the polymer has a strong permeability to gases and liquids. Quite unique medical applications arising from these features include: incompatible materials, such as drugs, can be incorporated into silicone-based pressure-sensitive adhesive (PSA) repair materials. The drug is placed in the free space within the silicone matrix. The rate is controlled by the silicone matrix (such as filler level, type, additional additives and cross-linking density), and the drug is then released at a designed rate. The drug slowly seeps out of the silicone matrix and is then absorbed by the skin. Drug delivery systems are a relatively new field that can be applied to anything from vitamins and drugs such as nitroglycerin to antibiotics.