Citric Acid-Mediated Liquid–Liquid Phase Separation of Polyphenol-Polyethylene Glycol for Tough Adhesives

Adhesives are essential in diverse industrial fields, and bioadhesives play a critical role in medicine for minimally invasive tissue repair and device integration. However, existing systems, particularly polyethylene glycol (PEG)-based adhesives, often suffer from brittleness, inadequate performance under extreme temperatures, and limited substrate versatility. To overcome these challenges, we developed a novel polyphenol-PEG adhesive platform through citric acid (CA)-mediated liquid–liquid phase separation (LLPS). This process, driven by CA-regulated hydrogen bonding as confirmed by XPS, FTIR, UV spectroscopy, and solution studies, produces adhesives with exceptional properties: peel strength near 15 N/cm, shear strength exceeding 4 MPa on hydrophilic substrates, rapid adhesion within 10 s, and operational stability from liquid nitrogen temperatures up to about 150°C, maintaining over 1 MPa shear strength at 200°C exposure. The adhesive demonstrates effective sealing of fractured bone, adhering to wet biological tissues and serving as an eco-friendly solution for restoring cultural artifacts. This study establishes the condensate formed by the CA-regulated LLPS process in the polyphenol-PEG system as a novel, ultra-robust adhesive suitable for demanding biomedical and industrial applications.