Solvent-Free One-Pot Preparation of Lignin-Ferric Nanoparticles for Enhanced Antibacterial Therapy

The global rise of antibiotic-resistant bacterial infections has intensified the need for scalable and biocompatible antimicrobial nanomaterials. Lignin is an abundant renewable biopolymer with intrinsic antimicrobial activity, but its limited aqueous processability and modest antibacterial efficacy restrict its direct application.

Lignin-ferric nanoparticles (LS-Fe) were prepared through an aqueous one-pot process using sodium lignosulfonate (SLS) as the lignin precursor and Fe³⁺ as the coordination component, without the use of organic solvents. The nanoparticles were characterized for size, dispersity, surface charge, morphology, Fe incorporation, and batch-to-batch reproducibility. Their antibacterial activity against Staphylococcus aureus and Escherichia coli, effects on bacterial growth, biofilm biomass, membrane integrity, intracellular reactive oxygen species (ROS), and lipid peroxidation were evaluated. Fe/ROS-modulation experiments were performed using deferoxamine, thiourea, catalase, and H₂O₂. Exploratory in vivo efficacy and safety were assessed in a small mouse model of S. aureus-infected wounds.

LS-Fe formed stable colloidal nanoparticles with a hydrodynamic diameter of 126.63 nm, a polydispersity index of 0.19, and a zeta potential of -44.7 mV. In preliminary in vitro assays, LS-Fe showed a descriptive trend toward greater antibacterial activity than pristine SLS against both bacterial strains. LS-Fe treatment was associated with increased intracellular ROS and lipid peroxidation, bacterial membrane damage, inhibition of biofilm formation, and reduced residual biomass of preformed biofilms. The attenuation of LS-Fe-mediated antibacterial activity by deferoxamine, thiourea, and catalase, together with its enhancement by exogenous H₂O₂, supported a possible Fe-mediated oxidative antibacterial contribution. In the exploratory infected-wound model, topical LS-Fe treatment was associated with faster wound closure, reduced bacterial burden, and improved histological features of wound repair, while no obvious histopathological abnormalities were observed in major organs at the tested dose.

Aqueous one-pot preparation of LS-Fe provides a simple organic-solvent-free strategy for integrating lignin nanoparticle formation with ferric functionalization. The preliminary findings support further investigation of LS-Fe as a sustainable antibacterial nanomaterial for infected-wound management, while larger confirmatory studies and more comprehensive mechanistic and safety evaluations remain necessary.