Adhesive Polyelectrolyte Complex Coacervates with Structural Antibiotics

Fast-acting adhesives that bind underwater are needed for many applications. Complex coacervates, viscous, hydrated phase-separated materials, have recently shown much promise as adhesives that can be used in wet environments. Here, negative polyelectrolytes, poly(styrenesulfonate), PSS, and poly(acrylamidomethylpropanesulfonate), PAMPS, were complexed with the positively charged antibiotics neomycin and streptomycin. Opposite charges on these components pair, yielding materials that have ideal viscoelastic properties for use in pressure-sensitive "instant" adhesion in aqueous environments. PSS complexed with neomycin or mixtures of neomycin and streptomycin were about 20 °C above their glass transition temperatures at physiological use conditions (0.15 M NaCl and 37 °C) and provided up to 100 kPa and 80 J m^-2 of adhesion strength and energy, respectively, at low strain rates. Underwater adhesion was observed on both hydrophilic surfaces, such as glass and metal, and hydrophobic surfaces, such as rubber. Although the antibiotic building blocks carried a low charge of 3+ or 6+, the interactions between their protonated amines and the aromatic sulfonate groups of the PSS were strong enough to provide stability, or salt resistance, against NaCl solutions with concentrations up to 1.7 M. An analysis of the equilibrium complexation (liquid-liquid phase separation) of small ligands with long polyelectrolytes showed how the salt resistance depends on the solution concentration of the ligand and how a sustained release mechanism is therefore built into these complex coacervates, allowing the antibiotics to kill Gram-positive and Gram-negative bacteria. Quantitative NMR measurements of buffered solutions of 0.15 M NaCl above the coacervates showed gradual release of antibiotics without significant release of the polyelectrolyte. This work introduces the use of underwater bioactive instant adhesive coacervates with competitive properties that are made from a polyelectrolyte and a small molecule.