Green synthesis of lignin nanoparticle in aqueous hydrotropic solution toward broadening the window for its processing and application

To exploit a green way to produce polymer nanoparticles using biodegradable and renewable macromolecules instead of petroleum-based ones, we initiated a novel and facile method to synthesize lignin nanoparticles (LNPs). The LNPs, having a hydrodynamic diameter ranging from ca. 80 to 230 nm, were formed by self-assembly in a recyclable and non-toxic aqueous sodium p-toluenesulfonate (pTsONa) solution at room temperature, with a lowest concentration of up to 48 g/L. We eliminated the unfavorable factors of restricted processing pH and lignin species by taking advantage of the hydrotropic chemistry and the synergistic dissociation of the entrapped pTsONa and intrinsic phenolic hydroxyl and carboxylic acid moieties of the LNPs. Because of the hydrotropic system, various water-soluble or water-insoluble drugs can be dissolved and encapsulated in the LNPs with an encapsulation efficiency of up to 90%. The drug-encapsulated LNPs also showed great properties, with sustained drug-releasing capability and biocompatibility. Furthermore, the unloaded drugs and free pTsONa could be easily recycled for multiple use, thereby achieving environmental sustainability. This synthesis approach with broad processing window could realize the industrial scale-up production of LNPs and have wide potential applications, including but not limited to versatile drug/bioactive macromolecule loading in the biomedical field.