Polyvinyl Alcohol/Lignin Composite Films Crosslinked with Citric Acid: Physicochemical Properties and Anti-Adhesive Activity Against Staphylococcus aureus

Antibiotic-resistant infections, particularly in hospital settings, are increasingly associated with biofilm formation on biomedical devices. An effective strategy to address this problem is the development of biopolymeric films with antibacterial and anti-adhesive properties. In this work, polyvinyl alcohol (PVA), a synthetic biodegradable polymer, was composited with lignin (LG), a biomass-derived polymer, and crosslinked with citric acid (CA) to obtain PVA-LG/CA gels/films. Materials were prepared with fixed PVA content (10% w/v) and varying LG (6.6 and 10% w/v) and CA (1–4% w/v) contents. FTIR and DSC analyses confirmed the role of CA as a crosslinker through esterification with the hydroxyl groups of PVA and LG. The lignin-free film (PVA/CA) showed the lowest water swelling (%Sw = 54.7), while PVA-LG/CA films exhibited significantly higher swelling, reaching 409.5%. All films were hydrophilic (contact angle < 90°). Increasing CA reduced porosity, whereas higher LG decreased hydrophilicity. Biological assays showed that films with higher LG and CA contents reduced bacterial adhesion. Overall, the formulation with 6.6% LG and 3.3% CA displayed the best performance, combining maximum swelling and minimal Staphylococcus aureus adhesion. These results highlight the potential of LG and CA as tunable components for modulating film morphology, hydrophilic balance, and bacterial interactions in biomedical material design.