Enhancing flexibility and antibacterial properties of PLA fibers via blending with PLA-based polyurethane and surface modification with ε-polylysine

Polylactic acid (PLA) fibers hold great promise in biomedicine and functional textiles, yet their inherent brittleness and lack of antibacterial properties limit widespread use. Conventional modifications often suffer from poor interfacial compatibility or potential cytotoxicity. Herein, we developed tough, antibacterial PLA composite fibers via scalable melt-spinning, using a rationally designed PLA-based polyurethane (PLA-PU) block copolymer as an interfacial compatibilizer and toughening agent, followed by surface immobilization of the natural antimicrobial peptide ε-polylysine (ε-PL). Intermolecular hydrogen bonding and identical PLA chain segments induce a favorable micro-phase separation, which acts as an effective stress concentrator to trigger massive shear yielding, significantly improving elongation at break while maintaining a robust tensile strength (73 MPa) suitable for medical textiles. The resulting topological roughness and micro-voids, combined with electrostatic interactions, provide robust physical anchoring sites for ε-PL, endowing the fibers with high antibacterial activity (>95% against E. coli and S. aureus ) and acceptable washing durability. This study elucidates the structure–property relationships in micro-phase separated biopolymer blends, offering a facile, eco-friendly, and biosafe strategy for engineering multifunctional PLA fibers for advanced biomedical applications.