Sulfur-based oxidation-responsive polymers. Chemistry, (chemically selective) responsiveness and biomedical applications

The introduction of low-oxidation-state sulfur atoms is a popular strategy to provide macromolecules with responsivity to oxidizing conditions, which in turn may confer them specific functionality (e.g. bioactivity or improved targeting). Indeed, reactive oxygen species (i.e. biologically relevant oxidants, ROS) at sufficiently low concentrations are essential for the healthy functioning of biological systems, but their overproduction is associated to a broad range of pathologies; chiefly, but by no means uniquely, those of an inflammatory character. Oxidation-sensitive materials therefore offer the possibility to perform two contemporaneous actions, i.e. direct ROS scavenging – with immediate anti-inflammatory effects - and ROS-triggered actions such as the release of appropriate drugs. In this review, we aim to acquaint the reader with the different strategies for the introduction of low-oxidation-state sulfur groups (thioethers, bis(alkylthio)alkenes, sulfoxides, thioketals, oligosulfides) in polymer structures, their responsiveness and their biomedical applications.