Engineering lignin-tannin nanoassemblies for multifunctional and sustainable skincare.

Lignin is increasingly recognized as a sustainable raw material for the development of safe and multifunctional cosmetic ingredients. Nanoengineering strategies enable its transformation into uniform colloidal particles with improved dispersibility and functionality. However, reducing its intense color without compromising its intrinsic bioactivity remains a major challenge for cosmetic applications. In this work, a function-preserving particle design strategy was developed by synergistically combining lignin with tannins at the nanoscale to create fully biobased phenolic colloidal assemblies. Four lignin-tannin colloidal systems (LTPs) were synthetized by combining softwood and hardwood kraft lignins with commercial tannins from chestnut and mimosa at different lignin-to-tannin ratios using an antisolvent precipitation method. The influence of polyphenolic components and processing conditions on particle size, morphology, and functionality was investigated. The resulting LTPs exhibited controlled particle dimensions in the range of 150-500 nm, together with superior multifunctional protective properties and improved aesthetic compatibility for skincare applications. Compared to colloidal lignin particles, LTPs showed improved antioxidant activity (75% reduction in IC₅₀), highly tunable UV-shielding capacity, and enhanced antibacterial effectiveness against Staphylococcus aureus, Streptococcus pyogenes, and Cutibacterium acnes, with minimum bactericidal concentrations (MBC) values between 0.77 and 2.48 mg/mL, while maintaining acceptable cytocompatibility depending on the particle composition at relatively high concentrations. Overall, this work presents a sustainable approach to engineering multifunctional bioactive colloidal materials from undervalued industrial by-products, highlighting their potential as skincare ingredients for cosmetic and pharmaceutical applications.