Self-Assembly of Stiff, Adhesive and Self-Healing Gels from Common Polyelectrolytes

Abstract

Underwater adhesion has numerous potential medical, household, and industrial applications. It is typically achieved through covalent polymerization and cross-linking reactions and/or the use of highly specialized biological or biomimetic polymers. As a simpler alternative to these covalent and biomimetic strategies, this article shows that stiff, gel-like complexes that adhere to various substrates under water can also be prepared through the ionic cross-linking of common, commercial polyelectrolytes. The gels form spontaneously when synthetic polycations, such as poly(allylamine) (PAH), are mixed with strongly binding multivalent anions, pyrophosphate (PPi) and tripolyphosphate (TPP). The PAH/PPi and PAH/TPP gels exhibit very high storage moduli (G∞′ ≈ 400 kPa), self-heal when torn, and adhere to both hydrophilic and hydrophobic substrates under water (with short-term tensile adhesion strengths of 350–450 kPa). Furthermore, these gels can be dissolved on demand (if adhesion needs to be reversed) by changing the ambient pH, which controls the ionization state of the polyelectrolyte and ionic cross-linker. These properties suggest that synthetic polycations cross-linked with PPi and TPP ions could provide a simple, inexpensive, and scalable platform for underwater adhesion.

Improved Concrete Materials with Hydrogel-Based Internal Curing Agents

“…Huang, et al [44], as well as Lawrence and Lapitsky [36], have utilized reversible ionic crosslinking between polyamines and multivalent anions to form stiff, adhesive, and self-healing gels. The amount of crosslinker required to form an effective gel was highly dependent on solution pH and ionic strength.…”

Ionically Cross-Linked Poly(allylamine) as a Stimulus-Responsive Underwater Adhesive: Ionic Strength and pH Effects

“…29 When mixed in aqueous solutions, certain combinations of polyelectrolytes and multivalent counterions can self-assemble into ionically cross-linked networks ranging from micro-and nanoparticles to macroscopic coacervates and gels. 30−37 Over the past decade, Wong et al have shown that the cross-linking of PAH with multivalent anions such as citrate and phosphate can produce coacervates with controlled drop sizes.…”

“…In the limit of very high TPP:PAH molar ratios, however, the excess of TPP bound to the surfaces of colloidal PAH/TPP complexes restabilizes the colloidal dispersions, thereby limiting the compositions for adhesive preparation to a narrow range of TPP:PAH ratios. 29 Another key property of these ionically cross-linked networks is their sensitivity to pH and ionic strength. We have recently shown that PAH/PPi and PAH/TPP complexes dissolve at pH 12 (where PAH becomes deprotonated) and when placed in concentrated acid (which reduces the ionization of the PPi and TPP).…”

Functional self-healing materials and their potential applications in biomedical engineering

“…Huang et al reported a unique strategy to synthesize adhesive and self-healing gels through ionic cross-linking between polycations poly(allylamine) (PAH) and pyrophosphate (PPi) or tripolyphosphate (TPP) [96]. Both PAH/PPi and PAH/TPP samples exhibited recovery of storage moduli to their original values within 10-30 min and attachment to various substrate under and above water.…”

“…17 Representative fluorescence microscopy images of a uncoated and b DNODN hydrogel coated microwell dishes after exposure to Caco-2 cells for 48 h. Alexa Fluor 488 and 4,6-diamidino-2-phenylindole (DAPI) were used to stain the cell membrane and the nuclei, respectively. (Reprinted with permission from [96]. Copyright 2015, Wiley-VCH.)…”