Nanoparticle Reinforcement of Poly(diol citrate)-Based Coacervate Adhesives

Abstract Tannic acid (TA)-based coacervate adhesives rely primarily on hydrogen-bonding interactions to maintain cohesion. However, these relatively weak hydrogen-bonds easily trigger cohesive failure in practical bonding applications, particularly under wet conditions. To address this limitation, a nanoparticle reinforcement strategy was employed in this study. A poly(diol citrate)-based coacervate adhesive (PN) was first synthesized via one-pot melt polycondensation of citric acid (CA), 1,8-octanediol (OD), and polyethylene glycol (PEG), followed by coupling with N-hydroxysuccinimide (NHS). Subsequently, TA-modified silica (TA-SiO2) and TA-modified chitin nanocrystals (TA-ChNC) were separately blended with PN and TA in aqueous solution to fabricate two types of nanocomposite coacervate adhesives, denoted as PNTS and PNTC, respectively. The results demonstrated that the cohesive strength, represented by peak stress, was significantly enhanced from 762.4 ± 94.1 kPa (pristine PNT) to 1266.1 ± 63.0 kPa (PNTS-3) and 2201.5 ± 187.6 kPa (PNTC-5), accompanied by a pronounced improvement in lap-shear adhesion strength: for the gel-type adhesives, from 36.6 ± 9.4 kPa (pristine PNT) to 56.4 ± 4.5 kPa (PNTS-3) and 74.4 ± 13.4 kPa (PNTC-3); for powder-type adhesives, from 27.1 ± 5.2 kPa (pristine PNT) to 36.3 ± 7.5 kPa (PNTS-3) and 73.3 ± 8.0 kPa (PNTC-3). Notably, TA-ChNC showed superior reinforcing effects in both gel and powder forms. Furthermore, the nanocomposite adhesives exhibited favorable cytocompatibility and antibacterial activity. Specifically, the PNTC adhesive achieved a hemolysis rate below 5%, together with shortened blood coagulation time and a low blood clotting index (BCI). In summary, the nanoparticle composite strategy effectively improved the overall performance of the coacervate adhesives.