<p>This study reports the design and optimization of multifunctional biocomposite films based on bacterial cellulose (BC), chitosan (CS), and green tea extract (GTE), with a primary focus on achieving controlled polyphenol release and durable antibacterial performance. A Box–Behnken design combined with response surface methodology (RSM) was employed to optimize film composition in terms of mechanical integrity, barrier properties, and bioactive release behavior. The optimized formulation (BC: CS = 60:40, GTE content = 2.44&#xa0;wt%) exhibited a tensile strength of 58.7&#xa0;MPa, elongation-at-break of 14.2%, low water vapor permeability (3.21 × 10⁻¹²&#xa0;g m m⁻²&#xa0;s⁻¹&#xa0;Pa⁻¹), and high antioxidant activity (86.3%). Release kinetics of polyphenolic compounds followed the Korsmeyer–Peppas model, indicating diffusion-controlled transport, with a cumulative release of 72.5% after 72&#xa0;h. The BC/CS–GTE films demonstrated strong antibacterial activity, producing inhibition zones of 20.5&#xa0;mm against <i>Staphylococcus aureus</i> and 17.8&#xa0;mm against <i>Escherichia coli</i>, together with excellent washing durability (&gt; 90% retention after 20&#xa0;cycles). Structural and thermal analyses (FTIR, XRD, and TGA/DSC) confirmed successful incorporation of CS and GTE through enhanced hydrogen bonding and controlled modification of the cellulose crystalline framework. Beyond the primary release–antibacterial function, the films also exhibited UV-shielding capability and affinity toward selected heavy metal ions, highlighting their potential as multifunctional bio-based materials. Overall, the results demonstrate that BC/CS–GTE films provide a robust platform for controlled delivery of natural polyphenols with durable antibacterial performance, relevant to sustainable coating and packaging-related applications.</p> Graphical abstract <p></p>