Ionically Crosslinked Polyelectrolytes As Materials for Stimulus-Responsive Underwater Adhesion and Long-Term Controlled Release

Ionic crosslinking of commercial polyelectrolytes can yield a wide variety of functional soft materials. Here, this approach is exploited to form gel-like complexes that adhere to both hydrophilic and hydrophobic surfaces under water by mixing poly(allylamine hydrochloride) (PAH), with either pyrophosphate (PPi) or tripolyphosphate (TPP). These complexes can deliver short-term adhesion strengths above 10⁵ Pa and can be dissolved on demand by changing the ambient pH. Their pH and salt sensitivity can also be utilized to tune their adhesion strength and to develop injectable adhesive formulations (which can be dispensed as low-viscosity dispersions that form adhesive films in situ). Furthermore, the high crosslink densities within the adhesive PAH/PPi and PAH/TPP networks enable them to serve as vehicles for controlled release (which for small molecules extends over multiple months). This suggests that ionic crosslinking of polyelectrolytes provides a simple route to preparing multifunctional materials, capable of both wet adhesion and long-term controlled release.