Figure 2 Characterization of hydrosoluble and photo-crosslinkable CS-MA.
(A) Solubility of CS and CS-MA in acid and neutral solution. (B)1H NMR spectrum of CS-MA. (C) FTIR spectrum of CS and
CS-MA.
The chemical structure of CS-MA was confirmed through the analysis of
its 1H NMR spectrum (Figure 2B). The signals at 5.40
and 5.62 ppm (g) indicated the presence of vinyl protons. The signals at
4.68 (a), 2.93 (b) and 3.42-3.76 ppm (c-f) were attributed to the
protons of the glucose ring, while the peaks at 1.94 ppm (i) and 1.81
ppm (h) represented the methyl protons of N-acetylglucosamine and
methacrylic anhydride residues. In contrast, CS did not exhibit any
signal at 5.5-6.0 ppm 23,24. Furthermore, the
successful reaction of CS with methacrylic anhydride was confirmed
through FTIR spectrum (Figure 2C). The appearance of new peaks at 1653
and 1538 cm-1 indicated the presence of C=O stretching
and N-H deformation/C-N stretching. The peak at 1588
cm-1, corresponding to –NH2,
disappeared due to its involvement in the newly formed amide bonds21.
3.2 CS-MA well stitched various
hydrogels
The hydrogel stitching comprised of two main steps, coating and
integration (Figure 3A), prior to the CS-MA polymerization, while the
T-peeling test process was illustrated in Figure S1. The optimal coating
and integrative time for the two PAAm sheets were determined to be 120
and 30 min, respectively (Figure 3B and 3C). Following the same
experimental procedure, the maximum adhesion energy was obtained for the
four types of hydrogels when bonded to each other (Figure 3D). The PAAm
layer adhering to another PAAm exhibited the highest adhesion energy of
140 N/m, while the adhesion energy between the PAAm hydrogel and Gel-MA
was the lowest at 3.2 N/m (Figure 3D). The peeling test revealed that
the hydrogel themselves cracked before the cohesive failure of the
bonded interface (Supplementary Movie 1). As Gel-MA had the weakest
mechanical strength among the four hydrogels, the Gel-MA sheet broken
before the adhesion failure, resulting in the low adhesion energy.
Hence, the adhesion energy at the interface of two hydrogels was mainly
determined by their mechanical strength rather than the bonding of
CS-MA.