Self-Healing Chitosan Hydrogels: Preparation and Rheological Characterization

Abstract

The paper aims at the preparation of chitosan self-healing hydrogels, designed as carriers for local drug delivery by parenteral administration. To this aim, 30 hydrogels were prepared using chitosan and pyridoxal 5-phosphate (P5P), the active form of vitamin B6 as precursors, by varying the ratio of glucosamine units and aldehyde on the one hand and the water content on the other hand. The driving forces of hydrogelation were investigated by nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction, and polarized light microscopy (POM) measurements. NMR technique was also used to investigate the stability of hydrogels over time, and their morphological particularities were assessed by scanning electron microscopy (SEM). Degradability of the hydrogels was studied in media of four different pH, and preliminary self-healing ability was visually established by injection through a syringe needle. In-depth rheological investigation was conducted in order to monitor the storage and loss moduli, linear viscoelastic regime, and structural recovery capacity. It was concluded that chitosan crosslinking with pyridoxal 5-phosphate is a suitable route to reach self-healing hydrogels with a good balance of mechanical properties/structural recovery, good stability over time, and degradability controlled by pH.

Erythromycin Formulations—A Journey to Advanced Drug Delivery

“…The hydrogels were thixotropic, having the ability to be injected through a 26-gauge needle which is widely used in biomedical applications. In vitro drug release experiments confirmed that gel encapsulation retarded the ERY release, and moreover indicated a pH-dependent release profile, a more rapid release being remarked in acidic pH (6.5), in line with the pH sensibility of the Schiff bonds which promoted a faster hydrogel degradation [ 136 , 137 , 138 , 139 ]. This is envisioned as a positive aspect, considering that infection sites have a slightly more acidic pH [ 140 ].…”

Chitosan Schiff-Base Hydrogels—A Critical Perspective Review

“…An increase in CHO ratio may occur due to a higher concentration in the aldehyde-bearing compound or a more intense oxidation reaction of the chosen polysaccharide. It was observed that, with the increase in aldehyde concentration, the network becomes stiffer and consequently the material exhibits a lower self-healing ability [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Moreover, some variables such as polymer concentration and solution pH have also been studied.…”

“…Moreover, some variables such as polymer concentration and solution pH have also been studied. In a paper by Craciun et al [ 23 ], the hydrogels were tuned in terms of water/solid content; the rheological studies indicated that the recovery properties increased along with the increase in water content. In another article, the authors reported on the influence of the pH and incubation time on the self-healing properties [ 19 ].…”

“…It has been noticed that the variation in concentration for the polymer solutions has a major impact on hydrogels prepared by this method; a decrease in chitosan concentration has similar impact to an increase in –CHO ratio [ 23 ]. Moreover, a lower polymer concentration may lead to better self-healing behavior and injectability.…”

“…However, it must be noted that these are dynamic crosslinks and therefore the hydrogels undergo structural modifications in time [ 23 ]. As the material “matures”, more crosslinks are formed and the network becomes denser and stiffer; macroscopically, the gel gets tougher and a change in color may also be noticed.…”