A Water-in-Water Emulsion Stabilized by Lignin-Containing Cellulose Nanofibers from Bamboo for Drug Delivery

Aqueous two-phase system (ATPS) Pickering emulsions offer an attractive alternative to traditional oil–water emulsions (e.g., W/O, O/W, and O/W/O) for cosmetics, food processing, biotechnology, and particularly drug delivery. However, their scope of application is hindered by instability and toxicity concerns. Thus, developing a safe, oil-free, and long-term stable water-in-water (W/W) Pickering emulsion based on ATPS remains a critical challenge. Herein, we innovatively developed a safe, oil-free, long-term stable water-in-water (W/W) Pickering emulsion stabilized by green bamboo-derived hydrophobic lignin-containing cellulose nanofibers (H-LCNFs) for drug delivery applications. Hydrophobic H-LCNFs were prepared from bamboo via deep eutectic solvent (DES) pretreatment coupled with facile hydrophobization and employed to stabilize dextran (Dex)/polyethylene glycol (PEG) ATPS-based W/W emulsions. Systematic investigation of PEG/Dex composition, H-LCNF concentration (0.1–0.5 wt %), and pH revealed that 0.3 wt % H-LCNF conferred exceptional long-term stability (negligible droplet size change over 7 days) through electrostatic repulsion under pH 7–9, while elevated pH enhanced electrostatic repulsion, imparting significant pH responsiveness. Crucially, this system achieved resveratrol (RSV) encapsulation efficiency (62.11% to 95.6%) and retention rate (59.84% to 89.18%) surpassing the current level for hydrophobic drug delivery. Overall, this green, nontoxic ATPS stabilization strategy unlocks high-value lignocellulosic biomass utilization and provides a reference value for the research field of drug delivery.