Xanthopterin-loaded kojic acid–functionalized β-cyclodextrin polymer coatings for UV shielding and antibacterial functionalization of 3D-printed PLA

This study describes the development of a multifunctional coating designed to enhance the antibacterial and photoprotective properties of 3D-printed Polylactic Acid (PLA). The strategy involves the synthesis of a β-cyclodextrin polymer (P-βCD) covalently functionalized with kojic acid (K) via a green aqueous-based process, followed by the supramolecular inclusion of xanthopterin (X) to yield the P-βCD-K-X complex. Structural confirmation was achieved through 1 H NMR, UV, and IR spectroscopy, while SEM analysis revealed a densely packed, particulate surface morphology. Broth microdilution assays demonstrated a stepwise functional enhancement, achieving a low minimum inhibitory concentration against Staphylococcus aureus (MIC = 0.18 mg/mL) and extending activity toward Gram-negative strains such as Klebsiella pneumoniae (MIC = 0.375 mg/mL) and Escherichia coli (MIC = 1.5 mg/mL). Surface-contact assays on coated PLA (5 mg/mL) revealed rapid antibacterial activity, achieving 88% bacterial inhibition within 5 min of contact and total bacterial suppression below the limit of detection (<100 CFU/mL) after 24 h. In vitro assays confirmed high cell viability (≥80%) in A549 cells across concentrations of 0.37–3.0 mg/mL. Optical characterization showed that coatings obtained from 5 to 10 mg/mL formulations lowered UV transmittance down to ≈1% near 350 nm and significantly boosted the Ultraviolet Protection Factor (UPF) of PLA from 9.2 (pristine PLA) up to 26.5 (10 mg/mL formulation), providing an “Very Good Protection” rating (BS EN 13758-1) by attenuating over 96% of harmful solar UV radiation. During accelerated weathering tests (96 h), while neat PLA photo-oxidized significantly (Carbonyl Index increased from 2.74 to 4.10), the functional coating prevented any net increase in surface oxidation (ΔCI = 0.00, maintaining a stable Carbonyl Index of 2.15). These quantitative findings highlight the potential of functionalized cyclodextrin polymers for engineering advanced, durable, and biocompatible antibacterial and photoprotective surface coatings.