Nanocomposite hydrogel films and coatings – Features and applications

•Nanocomposite hydrogels represent novel materials with synergetic features originating from organic polymer matrices and nano-size fillers.•Nanocomposite hydrogels have been extensively used as signal-switchable/tunable “smart” materials.•Nanocomposite hydrogels have been used in numerous biomedical applications, biosensor/bioactuator applications, bioelectronics, art preservation, biomolecular unconventional computing, etc. Different nano-species loaded into polymer hydrogels result in novel features of the composite materials and allow new applications. [Display omitted] Combining organic hydrogels with nanomaterials leads to creation of nanocomposite hydrogels (NCHs) with unique features. These multi-composite/multi-functional materials open possibilities for numerous applications in various areas of science and technology. The possible applications are based on highly desirable properties of the NCHs, such as electrical conductivity, mechanical reinforcement, (bio)catalytic and antimicrobial activity, magnetic features, anti-freezing and adhesive properties, self-healing ability, etc. These features can be achieved for the NCHs of different compositions. The fundamental NCH features are based on the properties typical for organic hydrogels, such as high solvent content, softness, high porosity/permeability, ability to absorb (bio)molecules and then their controlled release. Importantly, the NCHs can sharply change their properties upon a phase transition triggered by temperature changes or by presence of selected chemical species, e.g., pH change, operating as molecule signals. Additional features of the NCHs are provided by the nano-species entrapped in the organic matrices. These features can be synergistically combined with the properties of the hydrogel matrices resulting in unique materials demonstrating properties, which cannot be obtained either with organic hydrogel or with nano-species alone. This paper shows how these properties have been adapted to various specific applications and how NCH films and coatings contributed to the development in various areas of (bio)technology. The NCH applications in modification of electrodes, creation of electrochemical (bio)sensors, logical systems for release of substances, motion sensors, electrodes for health monitoring, antibacterial coatings and wound dressings, as well as materials used for artwork preservation are overviewed. The paper does not pretend to be a comprehensive review and the selection