Plasma oxidation pretreatment: a novel approach for plasma-induced hydrogel activation

Abstract Owing to the unique three-dimensional network structure with excellent mechanical properties and ability to store reactive oxygen and nitrogen species (RONS), plasma-activated hydrogel (PAH) has great potential in the biomedical field. However, polymer materials used to prepare hydrogels typically have antioxidant properties, which easily react with RONS and reduce loading efficiency. Here, we propose a simple and low-cost polymer oxidation method based on plasma oxidation pretreatment to enhance the loading capacity of polymers for RONS. Taking hyaluronic acid (HA) as an example, first, through discharge mode control, plasma (main RONS component is N 2 O 5 ) is generated in the transition mode to oxidize HA. The reductive hydroxyl groups adjacent to HA are oxidized to aldehyde groups, and low pH plasma oxidized pretreated HA (PHA) is obtained. To prevent the irritating effects of high concentrations of H + and aldehyde groups on the human body, we prepared acid-base neutralization PHA (NHA), in which we titrated an alkaline solution to neutralize H + and reacted with aldehydes to form hydroxyl and carboxyl groups. Further studies revealed that NHA does not have bactericidal effects by itself, but plasma-activated NHA has a greater RONS loading capacity and bactericidal effect than plasma-activated HA (PAHA), as well as lower irritation (one fifth of the H + concentration of PAHA). This study is expected to provide a strategy for promoting the preparation efficiency, bactericidal effect and biosafety of PAH.