Surface chemistry and bioactivity of colloidal particles from industrial kraft lignins

The morphology control of lignin through particle size reduction to nanoscale seems to be a suitable conversion
technology to overcome the intrinsic limitations of its native form to develop a wide range of biomaterials with
high performance. Colloidal lignin particles (CLPs) in the range of 150–200 nm were synthesised from hardwood
and softwood kraft lignins by the solvent shifting method. The initial molecular features of kraft lignins were
evaluated in terms of purity, molecular weight distribution, and chemical functionalities. The impact of the
lignin source and structure on the morphology, size distribution, and surface chemistry of CLPs was evaluated by
particle size analyser, SEM, TEM and 1H NMR. The results evidenced the influence of the botanical origin on the
morphology and surface chemistry of particles. Furthermore, the antioxidant properties and cytotoxicity of
lignins and corresponding CLPs, towards lung fibroblast cells were compared. CLPs from hardwood kraft lignins
exhibited higher antioxidant power against DPPH free radical and a higher cytotoxic effect (IC30 = 67–70 μg/mL)
against lung fibroblast when compared to CLPs from softwood kraft lignin (IC30 = ~91 μg/mL). However, the
cytotoxicity of these biomaterials was dose-dependent, suggesting their potential application as active ingredients
in cosmetic and pharmaceutic products at low concentrations.