Physicochemical characterization of bionanocomposite films based on tuna skin gelatin (Thunnus tonggol), squid ink melanin, and earthworm-derived glycolipoprotein G-90.

This study presents a sustainable strategy for developing multifunctional biopolymer-based composite films from marine and terrestrial bioresources. Gelatin extracted from Thunnus tonggol skin, melanin isolated from squid ink, and glycolipoprotein G-90 derived from earthworms were employed to enhance resource utilization within a circular bioeconomy framework. Four types of films namely gelatin, gelatin-melanin, gelatin-G-90, and gelatin-melanin-G-90 were fabricated and characterized for their structural, mechanical, physicochemical, and biological properties. ATR-FTIR spectra confirmed the successful incorporation of melanin and G-90, revealing strengthened hydrogen bonding and van der Waals interactions without altering gelatin's backbone conformation. Thermal analysis demonstrated that melanin improved stability by delaying degradation and enhancing water retention, while G-90 promoted synergistic stabilization in hybrid films. Contact angle measurements demonstrated tunable surface wettability, with melanin increasing hydrophobicity by 44 % (112.6 ± 9.1°), whereas G-90 introduced pronounced hydrophilicity by reducing WCA by ~57 % (33.8 ± 12.9°). Mechanical testing showed that melanin improved ductility and that G-90 alone reduced tensile strength but, when combined, produced a synergistic effect: the gelatin-melanin-G-90 film exhibited the highest elongation at break (101.6 ± 3.5 %, a ~ 200 % increase compared to pure gelatin) with moderate tensile strength (0.60 ± 0.1 MPa, ~51 % lower than gelatin). In vivo wound-healing evaluation revealed that the gelatin-melanin-G-90 film accelerated wound closure, enhanced angiogenesis, and supported nearly complete re-epithelialization. This work demonstrates a sustainable route for converting biological residues into thermally stable, mechanically flexible, and biologically active films with tunable wettability and strong wound healing performance.