Chitosan crosslinking with pyridoxal 5-phosphate vitamer toward biocompatible hydrogels for in vivo applications

Self-Healing Chitosan Hydrogels: Preparation and Rheological Characterization

“…Further, the intermolecular forces were confirmed by the shifting of the maximum of the broad band characteristic for the vibration of the hydroxyl, amine, and H-bonds between them, from 3300 cm −1 in chitosan to 3600 cm −1 in hydrogels. This was associated with the modification of the H-bond environment, as well documented for other chitosan hydrogels [20][21][22][23]31]. The occurrence of intermolecular forces was also demonstrated by the X-ray diffraction of the hydrogels when compared to pristine chitosan.…”

“…The formation of the imine units was confirmed on the one hand through 1 H-NMR spectra that displayed the occurrence of the specific chemical shift of imine proton around 9 ppm and on the other hand through FTIR spectra by the occurrence of specific vibration band of imine bond around 1602-1613 cm −1 (Figure 1a-d) [23,30]. It should be mentioned that 1 H-NMR spectra also revealed the presence of aldehyde proton, in agreement with an equilibrium state of the imination reaction, shifted to the products when the functional amine units were in excess compared to aldehyde ones [20,22].…”

“…These data indicate that chitosan hydrogelation was driven by the imination and physical forces induced by the newly formed imine units. On the other hand, POM images showed intense birefringence, the signature of an ordering degree (Figure 1f) [20][21][22][23][24][25]33]. Coupling X-ray and POM data, it can be envisaged that intermolecular forces directed a supramolecular arrangement of the imino-chitosan chains.…”

“…As the 1 H-NMR spectra indicated an equilibrium of the imination reaction, it is desirable to know how the stability (and implicit properties) of the hydrogels is affected by this equilibrium. 1 H-NMR spectra recorded over time (1, 7, 15, and 22 days) evidenced the progressive diminishing of the integrals of imine and aldehyde protons and the appearance of the enol proton (around 6.5 ppm) [23] for the hydrogels with high water content (those prepared with chitosan solutions 0.6% and 0.43%) (Figure 3a). This suggested that a too diluted system favored the shifting of imination to the reagents and the stabilization of the enol form of aldehyde.…”

“…Our studies in the field of chitosan hydrogels demonstrated a new crosslinking route of chitosan with monoaldehydes, based on the formation of imine units and self-assembling into clusters with the role of crosslinking nodes [20][21][22][23][24][25][26]. The method is promising, giving access to a large variety of multifunctional hydrogels, whose properties can be tuned by a proper choice of the monoaldehyde crosslinker.…”