Preparation and Biological Activity of Lignin-Silver Hybrid Nanoparticles

Silver nanoparticles (AgNPs) are excellent antimicrobial agents and promising candidates for preventing or treating bacterial infections caused by antibiotic resistant strains. However, their increasing use in commercial products raises concerns about their environmental impact. In addition, traditional physicochemical approaches often involve harmful agents and excessive energy consumption, resulting in AgNPs with short-term colloidal stability and silver ion leaching. To address these issues, we designed stable hybrid lignin-silver nanoparticles (AgLigNPs) intended to effectively hit bacterial envelopes as a main antimicrobial target. The lignin nanoparticles (LigNPs), serving as a reducing and stabilizing agent for AgNPs, have a median size of 256 nm and a circularity of 0.985. These LigNPs were prepared using the dialysis solvent exchange method, producing spherical particles stable under alkaline conditions and featuring reducing groups oriented toward a wrinkled surface, facilitating AgNPs synthesis and attachment. Maximum accumulation of silver on the LigNP surface was observed at a mass reaction ratio m_Ag:m_Lig of 0.25, at pH 11. The AgLigNPs completely inhibited suspension growth and reduced biofilm development by 50% in three tested strains of Pseudomonas aeruginosa at a concentration of 80/9.5 (lignin/silver) mg L^-1. Compared to unattached AgNPs, AgLigNPs required two to eight times lower silver concentrations to achieve complete inhibition. Additionally, our silver-containing nanosystems were effective against bacteria at safe concentrations in HEK-293 and HaCaT tissue cultures. Stability experiments revealed that the nanosystems tend to aggregate in media used for bacterial cell cultures but remain stable in media used for tissue cultures. In all tested media, the nanoparticles retained their integrity, and the presence of lignin facilitated the prevention of silver ions from leaching. Overall, our data demonstrate the suitability of AgLigNPs for further valorization in the biomedical sector.