This critical review outlines the current state-of-the-art research on the reversibly switchable wettability of surface brought about by external stimuli and the exchange of counterions. Chemical composition and surface topography are the two key factors in the wettability of solid substrates. Applying external stimuli and exchanging counterions of ionic liquids and polyelectrolyte films are valuable approaches for rendering the change in surface chemistry and/or topography, and for driving the transition between hydrophilicity and hydrophobicity of surfaces. Through the combination of stimuli-responsive films and micro-/nanostructural surfaces, smart surfaces with reversible switching between superhydrophobicity and superhydrophilicity have been achieved. As an important advancement in reversibly switchable wettability, this review briefly introduces ionic liquids (ILs) as on–off systems to obtain reversibly switchable wettability and then discusses in more detail the methods to induce the reversibly switchable wettability of surfaces modified by ILs, additives, or thin films. In addition to reversibly switchable wettability mechanisms, open problems and potential solutions are discussed (157 references).

Supported ionic liquids (SILs), which refer to ionic liquids (ILs) immobilized on supports, are among the most important derivatives of ILs.

Polyphenols, due to their high biocompatibility and wide occurrence in nature, have attracted increasing attention in the engineering of functional materials ranging from films, particles, to bulk hydrogels. Colloidal particles, such as nanogels, hollow capsules, mesoporous particles and core-shell structures, have been fabricated from polyphenols or their derivatives with a series of polymeric or biomolecular compounds through various covalent and non-covalent interactions. These particles can be designed with specific properties or functionalities, including multi-responsiveness, radical scavenging capabilities, and targeting abilities. Moreover, a range of cargos (e.g., imaging agents, anticancer drugs, therapeutic peptides or proteins, and nucleic acid fragments) can be incorporated into these particles. These cargo-loaded carriers have shown their advantages in the diagnosis and treatment of diseases, especially of cancer. In this review, we summarize the assembly of polyphenol-based particles, including polydopamine (PDA) particles, metal-phenolic network (MPN)-based particles, and polymer-phenol particles, and their potential biomedical applications in various diagnostic and therapeutic applications.