Figure 6. Structure, properties, and applications of collagen and gelatin-based adhesives.

(A) Collagen-based adhesives. (i) 3D structure of collagen; collagen triple helix with sequence (POG)₁₀, (ii) The top view of helical twist in the collagen structure. The top view of the T3–785 peptide (crystal structure), represents the first three POG triplets on each chain. Adapted from Bella [138] with permission from Portland Press, copyright 2016, (iii) Schematic representation of the mechanism of crosslinking of collagen (or gelatin) in the presence of transglutaminase. Transglutaminase enzyme forms amide bonds between the acyl groups in glutamine and the amino groups in lysine present in the protein (collagen or gelatin) chains. Adapted from Zhao et al. [152] with permission from Elsevier, copyright 2016; (B) Collagen and vitrigels. (i) Schematic explanation of the effect of vitrification temperature and time on the microstructure of collagen vitrigels. Insets are SEM images of the corresponding collagen vitrigels. Adapted from Calderón-Colón et al. [151] with permission from Elsevier, copyright 2012, (ii) Rabbit eye model with stromal wound treated with collagen vitrigel membrane and fibrin glue. Adapted from Chae et al. [163] with permission from Wiley, copyright 2015. (C) Gelatin-based adhesives. Optical coherence tomography (OCT) of a rabbit eye with retinal detachment treated (i) with gelatin or (ii) gelatin crosslinked with transglutaminase as observed 3 days of application. Images of histology transversal cuts of (iii) untreated and (iv) treated eyes three days after treatment. Gelatin-mTG adhesives tightly adhered to the retinal surface. Adapted from Yamamoto et al. [164] with permission from Springer, copyright 2013, (v) Transparency of gelatin and atelocollagen films after under wet conditions, (vi) Strain vs stress curves for different gelatin hydrogel films. Adapted from Watanabe et al. [170] with permission from Mary Ann Liebert, copyright 2011.