Solvent-free castor-oil–derived isocyanate adhesive with high bond strength and biocompatibility

Growing demand for sustainable bonding technologies has intensified the search for high-performance bio-based adhesives that can replace petrochemical systems without compromising mechanical integrity or environmental safety. A critical gap persists in solvent-free, castor-oil-rich formulations that simultaneously deliver high bond strength and verified biocompatibility. We addressed this gap by developing a one-pot, high castor oil usage, solvent-free protocol in which castor oil was urethanized and chain-extended with isophorone diisocyanate at NCO:OH ratios from 3/2 to 7/6. The adhesives were characterized by Fourier Transform Infrared Spectroscopy (FTIR)，Thermal Gravimetric Analyzer (TGA)，Differential Scanning Calorimetry (DSC), 180° peel, lap-shear, cytotoxicity and in vivo biosafety assays. The optimized composition (R = 5/4) exhibits a glass-transition temperature of −30.0°C and a 5% mass-loss temperature of 250.6°C; at 70% bio-based content it delivers a 180° peel strength of 37.2 N/25 mm and a lap-shear strength of 256.0 kPa, exceeding values reported for representative commercial tapes (0.3–4.4 N/in). Cytotoxicity screening on L929 and Vero cells revealed ≥84.0% viability, and murine patch and wound studies showed no erythema, inflammation, or tissue necrosis. These findings establish a scalable route to high-bio-content adhesives that meet industrial performance criteria and satisfy emerging biomedical safety standards.