Small interfering RNA silences specific genes by interfering with mRNA translation, and acts to modulate or inhibit specific biological pathways; a therapy that holds great promise in the cure of many diseases. However, the naked small interfering RNA is susceptible to degradation by plasma and tissue nucleases and due to its negative charge unable to cross the cell membrane. Here we report a new polymer carrier designed to mimic the influenza virus escape mechanism from the endosome, followed by a timed release of the small interfering RNA in the cytosol through a self-catalyzed polymer degradation process. Our polymer changes to a negatively charged and non-toxic polymer after the release of small interfering RNA, presenting potential for multiple repeat doses and long-term treatment of diseases.

There has been a resurgence in the development of new synthetic methods to produce stable organic radical polymers (ORPs) with control over chemical composition and structures. This has resulted from the new applications (e.g. electrochemical energy storage to synergistic therapy in drug delivery) that require sophisticated control over the polymer structural properties to compete in the market. Here, we provide a comprehensive overview of the synthetic strategies for making ORPs, discuss the synthesis–structure–property relationship and summarise the main applications of ORPs found in the literature so far. We envisage that the future development on ORPs will be to create ORP based smart materials through advanced macromolecular design and synthesis for better practical performance in diverse applications.