Abstract
The rheological changes that occur during the chemical gelation of semidilute solutions of chitosan in the presence of the low-toxicity agent glyceraldehyde (GCA) are presented and discussed in detail. The entanglement concentration for chitosan solutions was found to be approximately 0.2 wt.% and the rheological experiments were carried out on 1 wt.% chitosan solutions with various amounts of GCA at different temperatures (25 °C and 40 °C) and pH values (4.8 and 5.8). High crosslinker concentration, as well as elevated temperature and pH close to the pKa value (pH ≈ 6.3–7) of chitosan are three parameters that all accelerate the gelation process. These conditions also promote a faster solid-like response of the gel-network in the post-gel region after long curing times. The mesh size of the gel-network after a very long (18 h) curing time was found to contract with increasing level of crosslinker addition and elevated temperature. The gelation of chitosan in the presence of other chemical crosslinker agents (glutaraldehyde and genipin) is discussed and a comparison with GCA is made. Small angle neutron scattering (SANS) results reveal structural changes between chitosan solutions, incipient gels, and mature gels.
Highlights
IntroductionHydrogels exemplify an appealing class of soft materials with specific functionalities, and they have emerged as three-dimensional matrices for biomedical applications, including regenerative medicine and drug delivery systems [1,2]
Before the results from the gelling systems are presented and discussed, the choice of the chitosan concentration that is utilized in this work will be debated
The findings demonstrate that a systematic rheological classification of the gelation process can be conducted, both in the pre-gel and the post-gel stages by using GCA
Summary
Hydrogels exemplify an appealing class of soft materials with specific functionalities, and they have emerged as three-dimensional matrices for biomedical applications, including regenerative medicine and drug delivery systems [1,2]. Hydrogels are physically or chemically crosslinked hydrophilic polymer chains forming a three-dimensional network capable of absorbing large amounts of water. One important member of this class of gel-forming materials is chitosan, a linear copolymer of β-(1-4)-linked 2-acetamido-2-deoxyD-glucopyranose and 2-amino-2-deoxy-D-glucopyranose, generally obtained by alkaline deacetylation from marine chitin [3,4]. In contrast to many other polysaccharides, chitosan dissolved in acid aqueous media is positively charged because of protonation (the degree of protonation depends on the pH of the medium) of primary amines on the chitosan chains, which give the polymer a polyelectrolyte character. Chitosan exhibits many favorable biomedical characteristics, such as biodegradability, nontoxicity, and biocompatibility [5]
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