In this article, we consolidate several literature reports in an attempt to provide a structural definition of a polymer brush as a tethered polymer layer with a high grafting density of polymer chains. We will try to distinguish a brush from grafted polymer layers and coated layers and provide a reasonable approach to the description of the brush regime with a single parameter Σ—reduced grafting density. Furthermore, we will attempt to describe the relevance of this description to applications. This article is timely given the continuing interest relating to brushes on flat substrates, nanoparticles, and the walls of micro‐channels. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3505–3512, 2007

In this brief review we address a range of interesting applications and prospects of responsive hydrogel thin films for the fabrication of “smart” responsive surfaces, membranes, sensors with various transduction mechanisms, micro/nanoactuators, and capsules. We show that hydrogel thin films compete with grafted polymers and demonstrate strong advantages for the fabrication of robust multifunctional and multiresponsive surfaces. This article reviews recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly, as well as examining those publications to determine a range of applications.