Additives are minor but critical components that polymers need for processing and applications. However, these additives may also have adverse effects, e.g. for polymeric biomaterials, leaching additives can change surface properties, and may lead to poor biocompatibility. How to use additives yet keep them from detrimental behaviors is a challenging issue. Diffusion barriers may be used to slow down the additive migration but difficult to stop it. In this paper, we introduce the concept of "nano-adsorbents" in polymers. These nano-adsorbents confined the additives within the polymers by thermodynamically interacting with them. While the additives are still present in polymers to provide intended functions, they are thermodynamically constrained from free migration to the surface. Nano sized-fillers were selected due to their high surface to volume ratio. This new usage of nano-fillers for polymers was demonstrated with a biomedical polyurethane and a surface coated nanoclay that thermodynamically attracts the additive in the polyurethane. (c) 2007 Elsevier Ltd. All rights reserved.