11.2.1.1　Bioinspired adhesive hydrogels

Inspired by the fascinating biological structure and functions，bioinspired hydrogels have a broad application prospect in the biomedical field.Among them，taking inspiration from the underwater adhesion of natural mussels，barnacles，and other marine organisms，bioinspired adhesive hydrogels have received more and more attention in recent years.Bioinspired adhesive hydrogels refer to hydrogels with high adhesion and biocompatibility，which can replace traditional surgical suture wound closure devices and have the effect of promoting wound healing.The adhesion mainly comes from the interaction between the active groups in the polymer and the active groups in the biological tissue or the multiple supramolecular interactions with the surface.For example，some hydrogels with aldehyde groups can covalently bond with amino groups in biological tissues，thereby exhibiting high adhesion strength to living tissues.Duan et al.prepared an in-situ injectable viscous hydrogel by Schiff base reaction between the amino group of carboxymethyl chitosan and the aldehyde group of oxydextran.Injecting the hydrogel on the burn wound in rats can promote cell adhesion and make epithelial cells migrate to the wound area to promote skin regeneration.

The adhesive protein secreted by mussels has a fast curing speed，high waterproof adhesion ability，and excellent adhesion diversity in water，making it a biological adhesive with great advantages and potential.The catechol group，which is rich in mussel's adhesive protein，plays key roles in wet adhesion and adhesion diversification.Inspired by the strong underwater adhesion ability of mussels，a variety of mussel-like adhesion hydrogels have been developed.For example，Zhang et al.used polydopamine（PDA），reduced graphene oxide（rGO），branched polyethyleneimine（PEI），and polyacrylamide（PAM）to prepare a highly adhesive hydrogel film.After being attached to the wound，the hydrogel converted solar energy into heat energy and heated the wound locally.An increase of the local temperature at the wound site could reduce inflammation and promoted re-epithelialization，angiogenesis，and collagen deposition，thereby significantly promoting wound healing.Liu et al.synthesized a hyperbranched polymer HB-PBAE by the Michael addition reaction between polydopamine（PDA），poly（ethylene glycol diacrylate）（PEGDA700），and pentaerythritol triacrylate（PETA）.Then，HB-PBAE，poly（1-vinyl imidazole）（PVI），and gelatin solution were mixed，and Fe3+was added to prepare a bioinspired adhesive hydrogel.Fe3+can form coordination bonds with catechol group to stabilize the hydrogel.When the dressing needs to be changed，Zn2+aqueous solution can be sprayed on the dressing and the adhesive ability of the hydrogel is significantly reduced.At the same time，PVI and Zn2+form a stable coordination bond，which further enhances the strength of the hydrogel.It can be easily and non-destructively replaced，and there is no obvious dressing residue on the wound，which promotes wound healing（Figure 11-2）.This kind of dressing change promoted by metal ions may provide a new idea for the design of wound dressings.(https://www.daowen.com)