Electrospun Poly(vinyl alcohol) Composites Containing pH-Fractionated Kraft Lignin: Structural Characterization, Biocompatibility, and Immunomodulation.

Lignin and its derivatives exhibit attractive physicochemical and biological properties, including antioxidant, antimicrobial, and immunomodulatory activities; however, the relationship between lignin fractionation conditions and these biological effects remains poorly understood. Filling this gap is fundamental for the advancement of lignin-based materials in biomedical applications. In this study, Kraft lignin was fractionated by precipitation at three pH values (2, 5, and 8) and incorporated into poly-(vinyl alcohol) (PVA) matrices, which were subsequently processed by electrospinning. The components and the resulting composites were systematically characterized in terms of molar mass distribution, chemical structure, surface morphology, and colloidal properties using GPC, FTIR, SEM, zeta potential, and particle size analyses. The results demonstrated that pH-controlled fractionation significantly altered the molecular characteristics of lignin, dispersion behavior, surface charge, and filament morphologies. Notably, the lignin fraction obtained at pH 5 exhibited a favorable balance between particle size and colloidal stability, 339 nm and -38 mV, respectively. Biological evaluation revealed that all composites were cytocompatible with Vero cells, showing no significant reduction (less than 10%) in cell viability after 24 h of exposure. In contrast, immunological assays using human peripheral blood mononuclear cells (PBMCs) revealed distinct pH-dependent immune responses. The composite containing lignin fractionated at pH 5 preserved cell viability and selectively increased TNF-α production (p-value = 0.0008) without affecting IL-10 levels (p-value >0.05), indicating a controlled pro-inflammatory response. Overall, these results demonstrate that pH-guided fractionation is an effective strategy for adjusting the physicochemical and immunological behavior of electrospun PVA/lignin composites and identify the PVA-lignin system fractionated at pH 5 as a promising platform for biomedical applications requiring immunological modulation.