Water-based synthesis of cationic hydrogel particles: effect of the reaction parameters and in vitro cytotoxicity study

Micro/nanoscale hydrogel particles are of great interest for biomedical applications, such as carriers for therapeutic delivery. Compared to conventional hydrogel particles that are mainly composed of vinylic monomers, we have introduced a simple methodology to prepare multi-functional cationic hydrogel particles by adopting the epoxy–amine chemistry in water exemplifying “click” characteristics. Herein, we investigate the effects of key reaction parameters, including time, temperature, reactant concentration and amine–epoxy stoichiometric ratio, on the preparation and properties of such hydrogel particles. Our results indicated that the aforementioned parameters could greatly impact the particle formation. The hydrodynamic diameter, surface charge, and morphology of the resultant particles were characterized by dynamic light scattering and scanning electron microscopy. Particle size was inversely correlated with the following reaction parameters: reaction time, temperature, and reactant concentration. This is likely due to the influence of the parameters on the formation of the intermediate thermosensitive prepolymers. Different reaction conditions yielded a wide range of particle surface charges, varying from +47 mV to +71 mV. Morphological analysis also revealed significant effects induced by the variation of reaction time and temperature. All particles exhibited a temperature-dependent swelling property. However, the extent of swelling and sensitivity varied depending on the reaction conditions. Finally, in vitro cytocompatibility studies based on murine RAW264.7 macrophages showed the particle acute cytotoxicity being dose and surface charge dependent. Cytocompatibility of the cationic hydrogel particles was improved by reducing the surface charges with variation of the synthesis conditions.