A multi-functional reversible hydrogel adhesive

Designing and fabricating self-healing hydrogel adhesive is essential in many physical and biological applications such as wound closure and cartilage repair. In this work, a new type of hydrogel adhesive has been developed through ultraviolet (UV) curing acrylamide (AM) monomer and hyper-branched polyethylenimine (PEI) polymer. The synthesized PAM-PEI hydrogel (weight ratio for PEI: PAM = 1: 9) shows high stretchability (1D extension ratio > 5500 %) and good plasticity (it can be extended into 2D hydrogel film), quick self-healing property (within 30 s) at ambient enviornment and good adhesiveness to both inorganic (23 kPa similar to 90 kPa for metal and glass) and organic substrates (similar to 8 kPa for polytetrafluoroethylene, 1 similar to 7 kPa for skin and liver). More importantly, the adhesion-strip-cycle test suggested that the adhesion measured was reversible and did not attenuate for at least 5 cycles on various surfaces. Rheology tests have demonstrated the repeatability of self-healing behavior of the hydrogel between small (1%) and large (1000 %) strain. In addition, the self-healed hydrogel fragments show good injectability, which can be potentially used for 3D-printing. This work provides a facile way of preparing multifunctional hydrogel adhesive with potential engineering applications.