Figure 4.

Pre-polymerized or precursor solution-dependent tissue-stitching adhesives. (a) G-MA adhesive hydrogel for corneal repair: pregel solution penetrated into the cornea for visible light-crosslinking in the presence of photo initiators. (Reprinted from ref. [96] with permission from the American Association for the Advancement of Science.) (b) Polyacrylamide-alginate-Ca²⁺ adhesive hydrogel glued the tissue together via chitosan-EDC-NHS spraying to form amide interlinks and physical bonding by virtue of positively charged amines and negatively charged carboxylic acid. (Reprinted from ref. [78] with permission from the American Chemical Society.) (c) Chitosan and coupling agents (NHS and EDC) solution penetrate into tissues and PNIPAM–alginate hydrogel to form amide bonds. (Reprinted from ref. [99] with permission from the American Association for the Advancement of Science.) (d) Chitosan (pH < 6.5) penetrated into two PAM hydrogels, then formed new networks via NH₂-OH hydrogen bonding as the pH increased (pH > 6.5), which became entangled with existing gel networks. (Reprinted from ref. [100] with permission from John Wiley & Sons, Inc.)